Saturday, 14 September 2019

2S1 Gvozdika



The 2S1 "Gvozdika" was a workhorse self-propelled howitzer of the Soviet Army that served in motorized rifle units at the regimental level as well as in tank units, including the single tank regiment of motorized rifle divisions and tank regiments organized under tank divisions. The 2S1 replaced the towed D-30 howitzer in this role. Tank regiments were the first to receive the new self-propelled system and the BMP-equipped infantry regiments were second in line to be equipped with the 2S1, while BTR-equipped infantry regiments relied entirely on the D-30 until until the end of the Cold War. In practice, this meant that the bulk of the vehicles went to tank divisions as each division had three tank regiments and one infantry regiment fully equipped with BMPs. The 2S1 was also deployed in artillery divisions but their quantity depended on the specific division in question. Most Soviet artillery divisions operated a mixture of 2S1 and 2S3 howitzers with two "heavy" regiments armed with the 2S3 and one "light" regiment armed with the 2S1, but others were entirely equipped with the 2S3.

While massed assaults with shock units supported by highly concentrated massed artillery support was still part of the foundation of the Soviet Army offensive doctrine, it was emphasized to small unit leaders that they should expect to frequently participate in meeting engagements where the maneuvering forces of the two opposing sides meet unexpectedly and without preparation. The proliferation of the "Gvozdika" at the regimental level in the Soviet Army was designed so that highly mobile lower-level units could be provided with a high degree of self-sufficiency in combat as they could rely on responsive artillery support during fast-paced combat which could not be adequately provided if artillery was only available at a higher level of organization. Moreover, it should be noted that Soviet regiments were comparable to the U.S Army brigade in role, but were somewhat smaller in size which meant that the density of artillery was very high. As such, artillery support was more readily available both for indirect and direct fire purposes as dictated by the specific situation.


Additionally, it was necessary to replace the towed howitzers of the highly-mobile tank and BMP-equipped units with a self-propelled artillery system simply to keep up the pace of an offensive operation, whereas the BTR-equipped infantry units were less mobile, so the main advantage of having towed howitzers replaced with a self-propelled system would have been wasted. Of course, the idea of implementing self-propelled howitzers was by no means an original one by the late 1960's, but the mobility requirement was only firmly established at that time due to the unprecedented increase in the pace of the offensive.

During the late 1960's, the armour branch was beginning to receive the T-64, a revolutionary design that is now considered to be the first true main battle tank that boasted of an excellent power to weight ratio, a high top speed, long driving distance, excellent armour protection and a powerful gun. The tracked BMP, another revolutionary design that is now considered to be the first true IFV, was also becoming operational in the Soviet Army. It had excellent mobility that allowed them to keep up with main battle tanks. Without replacing the towed howitzers with self-propelled types, the increased operational mobility brought about by these new advanced tracked combat vehicles would have been nullified, or if the artillery elements were left behind during an advance, then the combat units would be left without artillery support. Both outcomes were unacceptable, so it was clearly necessary to develop a new generation of self-propelled howitzers to complement the recent technological advances of the Soviet Army. Indeed, in the article "Soviet Self-Propelled Artillery" published in the September-October 1978 issue of "Armor" magazine, author Larry W. Williams accurately pointed out that the then-recent introduction of new Soviet self-propelled artillery was not in response to Western developments, but rather, it was in connection with the increased demands of modern warfare.

However, the advantages of self-propelled howitzers over the towed type had always been evident even if there was no critical need for them until the appearance of main battle tanks and infantry fighting vehicles in the Soviet Army. The late appearance of the Soviet Army's first postwar self-propelled howitzer was partly due to the global obsession with missile technology from the late 1950's to the early 1960's, exacerbated by the personal intervention of Soviet Premier Nikita Khruschev in halting work on tube artillery in favour of focusing on rocketry.


As part of his large scale pivot towards missile technology and nuclear weapons, Nikita Khrushchev personally intervened to constrict the development of all types of tube artillery in 1955, resulting in most of the work on self-propelled artillery being discontinued. When Khrushchev's reign as Chairman of the Council of Ministers of the USSR was forcibly terminated on October 14, 1964, many of his policies affecting the Soviet military were reversed, one of them being the restriction on the development of self-propelled tube artillery. On the 4th of July 1967, the Central Committee of the CPSU and the Council of Ministers of the USSR issued resolution No. 609-201 decreeing the start of the development of new self-propelled howitzers. In accordance with this decree, the development of the first generation of Soviet postwar self-propelled artillery began. This generation included 122mm and 152mm howitzer systems and a 240mm mortar system, resulting in the creation of the 2S1 "Gvozdika", 2S3 "Akatsiya" and 2S4 "Tyulpan".


The 122mm D-30 was chosen to be the centerpiece of the new 122mm self-propelled howitzer at the very beginning, mainly to ensure that the commonality of ammunition was maintained when artillery units equipped with the D-30 were rearmed with the new self-propelled howitzer. Although some years had passed since the D-30 entered service, its tactical-technical characteristics were excellent and the artillery branch of the Soviet Army was satisfied with this howitzer so there was no perceived need for improvement. The new self-propelled howitzer would essentially be a D-30 on tracks with light armour to resist counter-battery fire when used in an indirect fire role or gunfire from small arms if it was used for direct fire.

Of course, a fully rotating turret was considered a mandatory feature as the vehicle needed to be capable of conducting all-round fire on a short notice to provide timely and effective fire support. The D-30 howitzer itself was already capable of all-round fire on a short notice thanks to its tripod mount, which was a noteworthy feature because one of the primary incentives to develop self-propelled guns with rotating turrets in the West was the inability for their towed guns to conduct all-round fire. Indeed, the all-round firing capability of the D-30 later proved to be a highly appreciated asset of Soviet forward bases in Afghanistan where it was the main artillery piece of the Soviet 40th Army as it allowed them to provide artillery support at a moment's notice in any direction - a feature that is still not available in the 105mm L118 and M119 light howitzers used by British and American forces in Afghanistan. It was only logical that the prospective new Soviet self-propelled howitzer would also have a feature that was already implemented in the D-30, unlike vehicles of WWII vintage like the German "Wespe", British "Sexton", American M7 "Priest" and the indigenous ISU-152, SU-122 and SU-76.

The vehicle also had to have a significant secondary anti-tank capability, and as such, it had to have a reasonably low profile and the ability to conduct direct fire using anti-tank ammunition. This was also a requirement shared by the D-30 howitzer in accordance with modern Soviet doctrine on the uses of artillery, towed or otherwise.


During the development of the prospective new self-propelled howitzer, a prototype turret with a D-30 in a new mount was created first and the tracked platform upon which it would be installed selected from other existing military vehicles. According to Russian historian A.V Karpenko, the selection was narrowed down to three options out of the myriad of choices in the vast arsenal of the Soviet Army:


  1. A modification of the GM-123 hull with five roadwheels instead of the original seven. This hull traces its roots to the SU-100P experimental tank destroyer and was widely used as a heavy universal tracked chassis in the mid-1960's. The most prominent examples are the 2P24 transporter-erector-launcher (TELAR) and 1S32 radar station of the 2K11 "Krug" surface-to-air missile complex.
  2. A modification of the Object 765 with a stretched hull and seven roadwheels instead of the original six. The Object 765 was the BMP-1.
  3. A modification of the Object 6 with a stretched hull, redesigned powerplant layout, relocated driver's station, and seven roadwheels instead of the original six. The Object 6 was the MT-LB.


The three options all used the same turret with the D-30 howitzer and all had a driving range of 500 km but differed quite significantly in their other properties. The prototype based on the GM-123 hull was quite heavy and had a very large ammunition capacity of 100 rounds. Despite a combat weight of 22.2 tons, it had a high top speed of 70 km/h thanks to its powerful 520 hp engine, but it was not amphibious. Its large weight and work capacity was deemed excessive for a 122mm howitzer system.

The prototype based on an extended Object 6 hull had a smaller ammunition capacity of 60 rounds and a lighter weight of 15.842. However, it retained the original 240 hp diesel engine of the Object 6 so it was not as quick as the other two options and had a lower top speed of 60 km/h. Like its parent design, it was amphibious with minimal preparation. However, it was an insufficiently stable firing platform.

The prototype based on an extended Object 765 hull was the preferred choice. It had an ammunition capacity of 60 rounds and it was slightly lighter than the prototype based on the extended Object 6 hull, it was readily amphibious, provided a stable firing platform, was quite speedy and easily transportable. It's worth noting that it was heavier than the BMP-1 itself with a weight of 15.164 tons but did not have an uprated engine, so although its nominal top speed remained the same at 65 km/h, it is quite likely that its acceleration and handling was affected.

The high tactical-technical characteristics of the Object 765 hull also made it an appealing option for the other artillery systems that were in development at the time. In 1969, the OKB-9 design bureau had a project to unify the "Akatsiya", "Gvozdika" and "Tyulpan" artillery systems on a single chassis based on the Object 765, where the products could have better characteristics than those created on the basis of MT-LB. Moreover, the Object 765 hull in its original configuration with six roadwheels was used as the platform for the new SNAR-10 radar system as it was considered the most suitable for this role. However, further work in this direction was hampered by the categorical refusal of the manufacturers of the Object 765, the Chelyabinsk Tractor Plant (ChTZ), to carry out the modifications needed for the installation of special equipment of any type. Moreover, the chief designer of ChTZ, Hero of Socialist Labor, USSR State Prize laureate P.P. Isakov used his influence to place a total ban on the use of his BMP to accommodate any form of special equipment. This decision also affected the development of the SNAR-10 radar system.

As a result of Isakov's antics, there was no choice but to continue the development of the "Gvozdika" using the extended Object 6 hull, and in the end, the "Akatsiya" and "Tyulpan" projects used the GM-123 hull. The ban on the use of the BMP as the carrier for special equipment was not lifted until Isakov departed ChTZ to become the director of VNII Transmash in 1974, paving the way for the ARK-1 "Rys" counter-battery radar system to be designed on the basis of the BMP-1 hull.

The first four prototypes of the 2S1 with the extended Object 6 hull were ready and tested in August 1969. The 2S1 "Gvozdika" was accepted officially into service on the 14th of September, 1971, together with the 2S3 "Akatsiya" with a 152mm howitzer and the 2S4 "Tyulpan" with a 240mm breech-loaded mortar. In connection with the simultaneous adoption of three new self-propelled artillery systems, the SNAR-10 radar reconnaissance system was also adopted at the same time, thus providing the new artillery systems of the Soviet Army with a crucial component of a modern fire control system.


Despite lagging behind Western nations in the use of self-propelled howitzers by more than a decade, the Soviet Union was able to completely eliminate the gap with their first postwar effort thanks to the maturity of their domestic arms industry. Indeed, when the 2S1 "Gvozdika" entered service, it was not only a very modern example of a self-propelled howitzer, but it easily qualified as one of the best vehicles of its type.

It is also worth noting that even though the various NATO members had continued to develop and produce new self-propelled tube artillery throughout the 1950's and early 1960's, the Warsaw Pact still retained a numerical advantage in the number of vehicles due to the extremely large stocks of ISU-152 and ISU-122 assault guns left over from the Great Patriotic War. However, despite a major modernization effort for the old ISU-122 and ISU-152 in 1958-59 to turn them into the ISU-122M and ISU-152M, the inherent limitations of these old assault guns made it impossible for them to fulfill modern requirements such as the ability to carry out all-round fire, so it is not surprising that the number of self-propelled guns was constantly dwindling after the conclusion of the Great Patriotic War. Nevertheless, the Warsaw Pact was not in any serious danger of being quantitatively overtaken by NATO in terms of self-propelled artillery as a class of weapons because the Soviet Union developed many highly effective multiple rocket launcher systems like the BM-14 with 140mm rockets and the BM-24 with 240mm rockets to supplement the older BM-8 and BM-13 systems which used 82mm and 132mm rockets respectively. Of course, the BM-21 "Grad" should also be mentioned as being an outstanding example of the superiority enjoyed by the Warsaw Pact in this class of artillery. The graph below, taken from the 1984 edition of "NATO and The Warsaw Pact Force Comparisons", shows the advantage held by the Warsaw Pact in the quantity of artillery from 1974 to 1984 as perceived by NATO intelligence.




With that said, the 2S1 was quite a simple vehicle compared to the modern main battle tanks fielded by the Soviet Army in the early 1970's. By the standards of other self-propelled howitzers, the "Gvozdika" was sophisticated in terms of its overall capabilities, yet it was cheap and simple to operate. Its qualities were not only appreciated in the army of its native country but also by foreign users such as the Finnish Army, who bought a number of vehicles from the ex-NVA in 1991.


ERGONOMICS





The "Gvozdika" has a conventional crew layout with the commander seated at the rear left quadrant of the turret, the gunner seated in front of him at the front left quadrant, and the loader occupying the entire right half of the turret. The driver is seated on the front left corner of the hull with the engine to his right and the transmission and final drives to his front.

During WWII, the USSR and Nazi Germany carried out independent research on self-propelled artillery design and reached the same conclusion regarding the layout of this type of combat vehicle. The optimal layout would have the engine and transmission and placed at the front, the driver would be seated next to the engine and behind the transmission, and the fighting compartment would be in the middle or rear together with the ammunition stowage racks. This provided the best working conditions for the crew and allowed ammunition to be easily passed into the fighting compartment through the hull rear while maintaining compactness of the vehicle. A major benefit of this layout was that the overhang of the gun or howitzer was kept to a minimum or eliminated entirely.

After the war ended, practically all known self-propelled guns and howitzers created internationally followed this layout regardless of whether they were open-topped or fully enclosed designs, or if they were turreted or not. In the USSR, self-propelled guns were actively being developed immediately after the war and the fruits of these labours were Object 105 (SU-100P) and Object 108 (Object 152G). However, no new Soviet self-propelled howitzers were created, although studies were conducted in the USSR from 1947 to 1953 in this direction.


The hull was derived the MT-LB, but it was not only lengthened with an additional pair of roadwheels. A basic MT-LB had the commander and driver seated side by side at the front, and had its engine installed in the center of the hull with the drive shaft connecting the engine and transmission passing between the seats of the two crew members. It was already decided that the commander would inhabit the turret of the new prospective self-propelled howitzer during the development of the new vehicle, so the MT-LB layout had to be drastically overhauled. This was the most rational distribution of weight and volume for a self-propelled howitzer, and of course, the lengthened ground contact length of the seven pairs of roadwheels made the "Gvozdika" hull a significantly more stable firing platform compared to the basic MT-LB hull. The MT-LB hull had a length of 6,262mm, whereas the 2S1 hull had a length of 7,260mm.

With a total length of 7,260mm and a width of 2,850mm, the 2S1 "Gvozdika" exceeds most main battle tanks in length and is ostensibly narrower, but this is only because it uses narrower tracks as a result of its low weight. When the width of its hull is compared to a tank like the T-54, the "Gvozdika" is somewhat wider, having a width of 2,100mm instead of 2,000mm.

The "Gvozdika" was not particularly tall compared to a Soviet medium or main battle tank as it had a height of 2,285mm when measured up to the turret roof, and its height was extremely modest when compared to typical Western self-propelled howitzers like the M109 as that had a height of 2,896mm when measured up to the turret roof. The "Gvozdika" is much closer to tanks like the Leopard 1 and the Chieftain in this respect. When measured up to the top of the OU-3GA spotlight on the commander's cupola, the "Gvozdika" is 2,740mm tall. Internally, the height of the fighting compartment is around 1,700mm. This is enough for a man of average height to stand with a bowed head but not upright since the standard issue boots and helmet add some additional height.

The turret ring diameter of the 2S1 was not listed in any publicly available literature that the author could find, but based on the drawings shown in the technical manual, the diameter is around 2,140mm. This is a little larger than the turret ring of the T-10 heavy tank (2,100mm) but smaller than the turret ring of the T-62 (2,245mm). It is worth noting that even though it is significantly smaller than the 2,500mm turret ring of the American M109, it is more than adequate for a self-propelled howitzer with a three-man turret which is an important distinction to make since the M109 had five men inside its turret of which only one was seated. The other four men had to be standing and moving around to carry out their duties. In the "Gvozdika", two of the three crew members in the fighting compartment fought from their seats and the third crew member, the loader, was greatly aided by a rational ammunition layout and a well-designed loading assistance device.




Thanks to the relatively large dimensions of its thinly armoured hull and turret, the 2S1 had a large internal volume that not only facilitated its amphibious qualities but provided good working conditions for the crew inside the vehicle, particularly for the loader who had enough space in the fighting compartment to move freely.

Inside, the fighting compartment is well-lit with three dome lights fitted on the turret ceiling. There is one dome light directly above the gunner's seat, one behind the commander's cupola, and one on the ceiling next to the howitzer.



VENTILATION



The ventilation system is installed in a large compartment in the turret bustle behind the commander's station. It can be accessed from outside the turret via a large rectangular hatch on the bustle roof.

The FVU-200 filter ventilator unit includes a supercharger that pressurizes the air inside the crew compartment including the driver's compartment which is physically isolated from the fighting compartment at the front of the hull. This was accomplished by dispersing the flow of air to the crew stations via a ducting system




The commander must use the lever handle behind his seat backrest to open the air intake for the ventilation unit.

COMMANDER'S STATION




The commander in a 2S1 was seated behind the gunner and was separated from the D-32 howitzer by a removable perforated sheet steel recoil guard. In combat, he was responsible for radio communications, relaying target position information to the gunner, and designating targets with his own surveillance instruments. He was also responsible for making the necessary calculations for firing upon map coordinates if the vehicle is used independent of a battery command network.

The commander's seat was attached to the turret ring. The seat is adjustable in height for the commander's personal comfort and it can be folded down flush against the turret basket. The commander's seat is higher than the gunner's seat, but the amount of headroom provided for him is similar because he has a cupola.




The cupola protrudes slightly above the turret roof and has the same thickness of armour as the turret, while the commander's hatch has the same thickness as the turret roof. The hatch has a dome-shaped bulge in the center to ensure that the commander has adequate headroom when he is positioned to use the periscopes. Overall, the cupola protrudes almost 20 centimeters above the level of the turret roof.




The internal surface of the cupola platform was marked with an azimuth ring that divided the full circle of the cupola platform into 6,000 mils (as per the Soviet definition) in major increments of 100 mils that were further divided into minor increments of 20 mils. When the cupola is aimed directly forward at the 12 o'clock position, an indicator needle fixed to the rotating cupola is aligned with the zero position of the fixed azimuth ring. The zero position of the azimuth ring corresponds to the 30-00 mil position. If, for example, the cupola is turned counterclockwise by 500 mils, the cupola will be in the 35-00 mil position and the indicator will point at the number "5" on the azimuth ring.




This simple and rather imprecise measuring system is only intended to allow the commander to be cued to a target or landmark by the battery commander or for the commander to cue the gunner to a certain bearing with just enough precision to allow the gunner to independently spot a target. For example, if the commander needs the gunner to look at a particular object in the distance, he orders the gunner to traverse the turret to the deflection angle reading of the azimuth ring.

As usual, the hatch becomes a protective shield for the commander when it is locked in the open position. For maximum protection, the commander can adjust the height of his seat so that he is minimally exposed when standing on it. Ideally, he should only have his head peeking above the edge of the hatch.




Like all contemporary Soviet tanks, the commander was furnished with a TKN-3B periscope, but this universal device was only supplemented by two TNPO-170A general vision periscopes to cover the forward 120-degree arc. The layout was typical for Soviet armoured fighting vehicles, but this meager array of periscopes would not have been acceptable for a tank. The amount of visibility offered by this cupola layout only corresponded to the commander's cupola of the BMP-1 which had the same number of periscopes in the same layout. It was more than adequate given the role of the "Gvozdika" due to the nature of the role that artillery played, even when used for direct fire. In fact, it could even be considered outstanding when compared with other self-propelled howitzers, since the FV433 "Abbot" had the same number of periscopes in the commander's cupola in the same layout but lacked a magnified periscope with a night vision capability like the TKN-3B. The commander of an M109 had even more limited visibility given that he relied entirely on a single forward-facing periscope.

In most cases, the advantage in vision and situational awareness that a 2S1 commander enjoyed did not really matter because the vehicle would most often be in a situation where it would be safe to fight with open hatches. As such, the "Gvozdika" would only have a real advantage over a contemporary foreign vehicle of its class when the crews are forced to fight with closed hatches. This may be because of an NBC threat or because of counter-battery fire.


The TKN-3B periscope in the 2S1 has already been discussed in other Tankograd articles and there is no sense in repeating what has already been said about this ubiquitous family of periscopes in this article. It is only worth mentioning that the target designation feature of the periscope was deleted due to the lack of a need for this feature on a self-propelled howitzer. Moreover, the electrical powered traverse system of the vehicle was quite rudimentary and could not support such a feature. Target designation would have been done with the help of the commander's cupola azimuth ring.


For communications, the 2S1 was equipped with the R-123 radio. It was mounted to the turret wall just next to where the commander would be seated, with its power supply unit mounted on the turret wall to its left. The R-123 radio had a frequency range of between 20 MHZ to 51.5 MHZ. It was mainly used to communicate with the battery command vehicle and with the other vehicles in the battery.




The commander's control panel, installed on the turret wall above the R-123 radio, was small and simple. On it were three toggle switches that allowed the commander to turn on the marker lights at the corners of the hull, turn on the supercharged blower of the ventilation unit (to generate an internal overpressure) and turn on the electrical power to the cupola to power up the TKN-3B periscope.





GUNNER'S STATION




Thanks to the relatively large volume of the turret, the gunner of a 2S1 not only had a seat but also had his own backrest, which was not present in a T-54 or T-62 due to the close distance between the gunner and the commander. Generally speaking, the gunner is comfortably seated, but unlike the gunners of Soviet tanks like the T-54, T-62, T-10, T-64 and T-72, 2S1 gunners were not provided with a unity periscope for general observation, so like the commander, he has significantly less overall visibility compared to his tanker counterparts in the Soviet Army. He relies entirely on his sighting instruments to survey his surroundings and he must either turn the turret while looking through the OP5-37 direct fire sight to view his surroundings or use his PG-2 panoramic sight, but generally speaking, he is completely subordinate to the commander during combat. This was not a major issue for a self-propelled howitzer simply because of its role and it is not surprising that the entire crew in the fighting compartment of the 2S1 has worse visibility compared to a tank crew.

The gunner has a control panel of his own, mounted on the turret wall above the turret azimuth indicator clock. The control panel contains fewer controls than the commander's control panel, but it has many more signal and warning indicators. Besides the three sockets at the bottom of the panel that connect to the turret, the entire panel is devoted to displaying valuable information to the gunner.




Across the top of the control panel, there is a signal lamp that indicates if the external howitzer travel lock at the front of the vehicle is stowed, a lamp warning that the driver's hatch is open, a lamp warning that the driver's windshield cover is open, a lamp warning that the rear door of the hull is open, and a readiness indicator lamp that signals if the electrical system in the turret is ready for operation. At the center of the panel, there is an instructional drawing that represents the vehicle with labels showing the permissible firing arc when the rear door is open and the size of the dead zone for the turret when the driver's hatch is open. When the turret is within the permissible firing arc of 120 degrees, the howitzer can be fired using its electric firing mechanism while the rear door of the hull is open, but if the turret is outside of this firing arc and the rear door is open, the electric firing mechanism is deactivated. When the turret is traversed while the driver's hatch is open, the electrical traverse mechanism is automatically braked when it reaches the designated sector around the driver's hatch. In this dead zone, turret traverse can only be accomplished manually.

At the left side of the panel, there is a toggle switch that allows the gunner to activate or deactivate the turret electrical traverse drive, and at the right side of the panel, there is a toggle switch that turns on electrical heating for the gunner's sighting instruments.

SIGHTING INSTRUMENTS




The 2S1 had basic sighting equipment for indirect and direct fire so that it could complete a fire mission independently of external fire control systems with the same accuracy as traditional artillery systems. However, this was normally not required as there was a network of artillery reconnaissance and fire control equipment to direct the "Gvozdika" more accurately. Like any other artillery complex of the 1970's, fire control was handled by surveillance vehicles like the PRP-3 that operated far forward of the howitzer batteries, and the SNAR-10 ground artillery reconnaissance radar operated at the division level. Moreover, the battery command vehicle integral to each battery carried a DAK-1 laser rangefinder. The main purpose of the laser rangefinder was to measure the range of reference points in the distance, but it could also be used to measure the range to enemy troops for direct fire.


The two sighting instruments installed in the 2S1 "Gvozdika" were the OP5-37 direct fire telescopic sight and the PG-2 panoramic sight. They were mounted side by side and take up minimal space.




However, the "Gvozdika" did not have the ability to carry out direct fire missions at night as it had no night vision sights or other suitable gunnery equipment for this purpose.


OP5-37 DIRECT FIRE SIGHT




The OP5-37 sight had a fixed 5.5x magnification and a field of view of 11 degrees. It can be independently elevated from -5 degrees to +20 degrees. The magnification of the sight was noticeably lower than that of a typical Soviet medium tank like the T-55 and T-62 (7x) or a heavy or main battle tank like the T-64 (8x), but it was adequate for the 2S1 due to the limited effective range of the howitzer. The viewfinder of the sight had the same type of markings and the same range adjustment mechanism used in Soviet tank sights since the TSh-16, first used in the later half of the Great Patriotic War.


As the viewfinder below shows, this particular sight was configured to allow direct fire with HE-Frag shells with a full charge and BK13 HEAT shells. It was also possible to fire different ammunition types or HE-Frag shells with reduced charges, but to do this, the gunner must refer to a firing table to obtain the necessary superelevation angle corresponding a desired firing range, and then use the mil scale on the right side of the viewfinder (marked 'ТЫС' in the photo below) to adjust the superelevation of the howitzer.




To adjust the range, the gunner turns the range adjustment dial protruding beneath the eyepiece of the sight to lower the range scales until the correct range increment aligns with the fixed horizontal line in the viewfinder. The center chevron in the viewfinder lowers together with the range scales, thus generating the ballistic solution. When the chevron is raised and placed onto the target, the howitzer gains the necessary superelevation angle.


Unlike a TSh-type sight, the OP5-37 was linked to the howitzer by a parallelogram linkage instead of a more direct coaxial linkage. However, due to the howitzer's large range of elevation angles and the rather limited range of angles permitted by the linkage system, the OP5-37 was designed to disconnect from the howitzer when its elevation angle exceeded +20 degrees and reconnect itself when the howitzer returned to this angle. The parallelogram linkage can be seen in the drawing below connecting the head of the sight to the trunnion pin of the D-32 howitzer.




The reason for the use of this type of mechanical link with the howitzer was because the howitzer was recessed rather far into the turret and its pivot point was therefore quite far behind the location of the sight, whereas the gun of a tank like the T-54 had its trunnion pin just behind the embrasure for the gun mask, so its pivot point was directly coaxial with the gunner's telescopic TSh sight.

The aperture window of the sight was partially shielded from the weather by a sheet metal hood, and the window itself had a manually-actuated wiper for the gunner to clean it of dust and rain.


PG-2 (1OP40) PANORAMIC SIGHT




The PG-2 was a conventional panoramic sight that could be used for both indirect and direct fire, but its main purpose is to allow fire corrections and target transfer for indirect fire. As one would expect, the sight provides a panoramic view in a full 360-degree circle. The vertical range of motion of the sight is limited to 3.55 degrees in elevation and depression. It had a fixed 3.7x magnification and a field of view of 10.5 degrees.





When used in its indirect fire role, the PG-2 sight has two range drums for the gunner to traverse the turret to a new bearing with various degrees of precision. The range drums are located behind the eyepiece of the sight and they are positioned so that the gunner can look through the eyepiece with his right eye and also see the range drums so that he can quickly adjust the deflection of the sight.

The two range drums are used to measure the deflection angle of the panoramic sight. The bottom drum has the coarse adjustment scale with increments of 100 mils per division. A full circle is divided into 6,000 mils under the Soviet definition, so there are 60 increments marked on the drum. The top drum has the fine adjustment scale with increments of 1 mil per division with 100 increments marked on the drum from 0 to 99. When the deflection of the sight is set to 30-00, the line of sight is parallel to the bore axis of the howitzer, and increasing the deflection angle offsets the sight counterclockwise whereas decreasing the deflection angle offsets the sight clockwise. 

To use the PG-2 to lay the howitzer on a target, the gunner uses the sight as a reference point checking instrument. Radio masts, telephone poles, windmills and other structures of a similar shape were considered the make for the best reference points as they are clearly visible from great distances and are easy to align with the vertical markings in panoramic sights. To use the PG-2 to aim the howitzer in azimuth, an external artillery director informs the battery commander to adjust the howitzers to a certain deflection angle relative to the reference point. For example, if a target is 660 mils to the right of a windmill, then the 2S1 gunner would set the PG-2 sight to the 36-60 setting, thus placing it 660 mils to the left of the bore axis of the howitzer. Then, when the gunner aims at the windmill, the howitzer would be laid 660 mils to the right of the windmill.




When deployed in a traditional line formation in equal intervals of 20 to 40 meters between each howitzer, it is easier to coordinate each tube to compensate for their own displacement from the firing line. This simplifies the calculations for accurate fire, thus enabling quicker reaction times to be achieved.

When not in use, the sight was fully retracted into the turret and a cover was closed over it. A rubber sleeve ensures that a hermetic seal is maintained regardless of whether the sight is raised or retracted. This can be seen in the drawing on the left below. The cover that is closed over the panoramic sight has the same armour thickness as the rest of the hull roof. It is manually operated by the gunner, with a handle on the turret ceiling for this purpose.




The short video clip below shows the PG-2 sight head being pushed through the rubber sleeve. Original video from Denis Mokrushin.





LOADER'S STATION



The loader in a 2S1 had little else to do but load the howitzer and arrange the ammunition. In connection with these duties, he was also responsible for setting the fuzes on shells and adjusting the weight of the propellant as required before each round is loaded. For general vision, he is provided with a single MK-4 periscope (Gundlach periscope) which gives him a decent all-round view of his surroundings.




The image below, taken from a show by TV Zvezda, shows an interesting perspective of a seated 2S1 loader grasping his MK-4 periscope for stability.




The photo below by Vladimir Yakubov shows the loader's periscope and hatch in more detail together with the ammunition racks affixed to the turret wall.




Some time after the beginning of the mass production of the 2S1, a circular port was added to the turret wall of the loader's station for the disposal of spent cartridge cases. It served as a safe and convenient opening for the loader to dispose of spent shell casings as he would not need to lift the casing up above his head and forcefully throw it out of his hatch, thus saving him energy and maintaining overhead protection. The photo below shows the port cover as viewed from outside the turret. It has been welded shut in this example, but the simple spring-loaded hinge mechanism can be clearly seen.




To use it, the loader must first unlock it by unscrewing and removing the crossbar that keeps the port cover tightly sealed, but after this, the loader can simply pick up a spent casing and push it out of the port with its base against the spring-loaded port cover. Once the casing clears the port, the cover automatically closes under spring tension.




Although it seems to offer a good alternative entryway for fresh cartridges when replenishing the ammunition of the vehicle as it led directly to the loader's station, it was not feasible to use the disposal port for this purpose because there was no way to keep it open without partly dismantling it, and even so, it would be redundant because the rear hatch in the hull was more than good enough.


LOADING ASSISTANCE DEVICE




The loader's work was made easier by a powered loading assistance device, but because the weight and size of 122mm ammunition was still quite manageable, a semi-automatic loading system with a mechanized ammunition rack such as the type used in the 2S3 "Akatsiya" was not deemed necessary. As such, the loader had to manually transfer projectiles and propellant charges from the fixed ammunition racks fitted around the vehicle into the loading assistance device. This was first serially implemented on the SU-122-54 tank destroyer and T-10 heavy tank, and it is a feature that the "Gvozdika" shares in common with many other vehicles of its type such as the M109 and the FV433 "Abbot". However, the specific design of the loading assistance device in the 2S1 was particularly good as it required minimal physical effort on the loader's part and most importantly, the device worked at all elevation angles but particularly well when the howitzer was aimed at a high angle.




The loading assistance device increases the rate of fire of the 2S1 on the whole, but it is most helpful for increasing the sustained rate because it substantially reduces the physical burden on the loader when the howitzer is fired for prolonged periods. Unlike a tank loader who is not expected to have many opportunities to expend his entire supply of ready ammunition, a howitzer loader was expected to expend hundreds of rounds of ammunition over the course of a few hours.

The two photos below show the loading assistance device from the perspective of the commander. The photo on the left shows the device in its standby position with the tray in the raised attitude, ready to accept a fresh shell, whereas the photo on the right, taken by John Manion and published in the Sportsman's Guide website, shows the loading tray lowered and ready for ramming while the device remains in the standby position.




To load the D-32, the loader must first receive the order to load a specific type of ammunition from the commander but in most cases, the loader's job is quite straightforward as he would only need to repeatedly load HE-Frag shells. If the 2S1 is ordered to complete a quick shoot-and-scoot fire mission lasting no longer than 5 minutes in duration, the loader would simply be told to load a specific number of shells in a sustained burst at the maximum possible rate or until the order to cease fire is issued.

The full loading procedure is demonstrated in a number of videos on YouTube and other video streaming sites, and it can be seen in the short clip shown below.




When loading, the loader picks up a projectile from the closest ready rack and places it on the loading tray. Then, he shoves the entire loading assistance device against the resistance of a pair of returns springs until the device is locked in place behind the breech, whereupon the ramming cycle immediately begins. The loading tray is automatically moved forward and the tray is tilted down onto the U-shaped channel behind the breech block, aligning the projectile with the barrel chamber, and the rammer simultaneously performs a full stroke to ram the projectile all the way down the gun tube to seat it properly against the rifling.

Immediately after moving the loading assistance device into position behind the howitzer, the loader locates and retrieves a propellant charge and adjusts the propellant weight unless he has already done so in preparation. By the time the loader has retrieved a propellant charge, the mechanism would have finished the ramming cycle for the projectile. When placing the propellant charge on the freshly vacated loading tray, the loader should ensure that the base of the charge is in contact with the rubber-padded tip of the chain rammer. Finally, the loader presses the big red "ram" button on the recoil guard just next to the howitzer breech, whereby the device sends the chain rammer to perform a short stroke to ram the propellant charge into the gun. Once the rammer is fully retracted, the loading tray is also automatically retracted and the device is immediately pulled back to the ready position by the return spring and locked in place, preparing itself to receive the next shell.


The firing mechanisms of the howitzer are disconnected by the loader's safety system until the loading process is complete. However, the loader can manually set the status of the howitzer firing mechanism from a control box on the recoil guard in front of the loading assistance device.


Before the first shot is fired, or rather, before the order to fire is received, the loader can preemptively place a shell on the loading tray and have a propellant charge ready in his hands. This is otherwise known as "laploading". It is safe for the shell to be readied in this manner because the tray is designed to prevent it from accidentally rolling off or sliding out, and it is not problematic for a self-propelled howitzer to be laploaded because the target does not change on the fly in a typical mission. It is only a potential problem for tanks because tanks are most often used for direct fire against a mixture of infantry, soft-skinned vehicles, lightly armoured fighting vehicles, other tanks, and fixed fortifications. This requires the loader to constantly switch between AP or APDS or APFSDS, HEAT, HESH, HE, and so on.

Unlike tanks, a howitzer is usually called upon to deliver a bombardment of the same ammunition type on a fixed area target, most often using HE shells. By enabling the loader to prepare a shell in advance, the burst rate of fire of the "Gvozdika" in the first minute of a barrage can be slightly higher than the average figures that are usually reported.


The loading tray of the loading assistance device is helpful in other ways as well. Besides allowing the loader to load more quickly, it also makes it more convenient for him to set the fuze. The fuze of a typical OF-462 shell is set to the HE-Frag mode at the factory and the loader can set it to the HE or Frag mode under orders from the commander. The decision on the most appropriate fuze setting comes from the artillery reconnaissance units.




The general design of the device is focused on facilitating the loader's work to the maximum extent when the howitzer is used for high elevation indirect fire. Unlike the very similar loading device in the T-10 heavy tank, the loading tray, shown in the drawing below, has tall side walls to ensure that the projectiles and propellant charges held inside are properly aligned with the bore axis and do not fall off regardless of the elevation angle of the howitzer.




When the howitzer is used for direct fire, the breech would tend to be either close to being completely level, or elevated by +3 degrees while the muzzle end is depressed by -3 degrees, or depressed by up to -3.6 degrees (60 mils) when the muzzle end is elevated by +3.6 degrees to exploit the maximum direct fire range permissible from the OP5-37 sight. At these angles, the loading assistance device is slightly less convenient for the loader to use since he has to lift a shell and a propellant charge to his shoulder level to drop it into the loading tray. In fact, the bump in the turret roof is meant to give the loader more space to do this when the howitzer is fully depressed, as the entire rear end of the howitzer would be quite close to the turret ceiling. The device does not restrict the loader in any sense and it is not an obstacle for the loader, and it is still effective at aiding him in his work, but it requires him to expend more energy to do the same task.


Once the tray is in position behind the breech, a microswitch is tripped and the chain rammer begins its ramming cycle. As the chain rammer travels forward, the loading tray is pushed forward by an actuator and this action causes it to tilt downwards by slide along a curved rail.




The loading tray is shown in the drawing below in its two principal loading positions: in the "ready" position and the "ramming" position. The drawing also shows the return springs that pull the device back to the "ready" position after the loading cycle is complete.




The device was a self-contained unit that could be removed from the recoil guard of the D-32 howitzer to revert to a fully manual loading method, so if the device fails completely, it is possible to load the howitzer manually. The loader inserts the projectile and propellant into the breech by hand and the commander participates by using a ramming staff to replace the powered rammer. To do this, he can fold down his seat and remove the recoil guard separating his station from the howitzer.


AMMUNITION STOWAGE





The vehicle carried 40 rounds of 122mm ammunition of which 24 were in the ready racks in the turret and 16 were in the reserve racks in the rear hull compartment. The ready racks on the turret wall and turret basket hold a propellant charges and projectiles respectively whereas the ready racks in the turret bustle mostly hold propellant charges.




The projectile racks hold their projectiles by cupping the tapered part of their boattails or by supporting them by the ring at the base. The projectiles are further secured by a quick-release tension latch.

The ready racks in the turret bustle contain 5 HEAT shells and 17 propellant charges. The HEAT shells were stowed in a special set of slots in the corner of the turret bustle where the greater length of the shells compared to the propellant charges would not interfere with the loader as they would not stick out into the fighting compartment.


The reserve propellant charge racks occupy both sides of the rear compartment, leaving a large empty space in the middle to allow the loader to retrieve the propellant charges freely. The top half of the rack held 8 propellant charges and the bottom half held 8 projectiles for a total of 16 rounds of ammunition. The two racks in the rear compartment were identical and were installed symmetrically.




The two photos below show the reserve racks being replenished with a new HE-Frag shell and a new propellant charge.




Besides simply allowing the propellant charge racks to be accessed, the empty space in the rear compartment had a variety of other functions. The most obvious function, of course, was that it could serve as a passageway for the crew to exit through the rear doors, but if the "Gvozdika" was used in a static position for sustained fire, this space would be used to link a conveyor chute from the rear door to the fighting compartment. The conveyor chute, shown in the drawings below, is a simple device with a fixed spine and a sliding tray that moves along the spine. Like a curtain rod, the spine of the conveyor fits over two crossbars that are screwed to special threaded holes at both ends of the compartment.




When disassembled into three individual parts, the conveyor is stowed inside the vehicle on the floor underneath the reserve ammunition racks. When needed, it is installed by the loader while the other members of the crew go about their own tasks. First, he opens the rear door and then he installs the conveyor crossbars, one of them just behind the frame of the rear door and the other just behind the turret basket. This only takes around 20 seconds to complete, as demonstrated in the short clip below. The original video is by Denis Mokrushin.




After installing the conveyor, the loader returns to his station and waits for ammunition to be fed into the vehicle. This was the responsibility of the assistant loaders riding in the ammunition carriers accompanying the "Gvozdika" battery.

Because the partial fence around the turret ring on the loader's side of the turret left an open area near the floor, it was possible for the ammunition supplied externally through the conveyor chute to reach the loader as long as the turret was aimed forward or to the right. If the turret was aimed to the left, the turret basket on the commander and gunner's half of the turret prevented the conveyor from reaching the fighting compartment.




Because of the restriction on the turret orientation for using the conveyor chute, it was necessary for the artillery battery to know the bearing of the target before positioning the 2S1 howitzers and preparing the ammunition carriers for external loading. This also meant that a 2S1 battery that was set up for sustained fire at a fixed target using an external ammunition supply needed time to readjust its position if it received orders to fire at a new target to the left. That said, the battery could still immediately react to a sudden contact with enemy forces by simply having the conveyors dismounted, thus enabling the turret to freely rotate for all-round fire.


Depending on the particular ammunition rack that was to be replenished, the crew would either pass ammunition into the vehicle through the rear hatch or through the loader's hatch.





RATE OF FIRE

The rate of fire of artillery systems was not only an important measure of the amount of destruction that can be caused, but it was also pivotal to the survival of the system itself. If the artillery system must remain in a single firing position for a prolonged period to complete its mission, its chances of survival drop drastically for a variety of reasons. The most dangerous threat was the counter-battery radar equipment of the enemy as it could track incoming shells and compute the location of the battery with an error margin of just tens of meters. This was sufficiently precise to form fire control commands to direct accurate counter-battery fire. Another threat was aerial reconnaissance, which was more acute for Soviet artillerymen than for their NATO counterparts simply because of the low expectation that the Soviet air force could maintain air superiority. While some local sectors may enjoy a sky controlled by Soviet fighters, it was reasonable for most artillerymen to expect the aircraft over their heads to belong to enemy forces. As such, it was also reasonable to expect that even individual artillery batteries engaged in sustained fire would be visible to enemy air reconnaissance from long distances due to a large smoke signature.

The most straightforward solution to this problem is to increase the rate of fire of the artillery piece, thus maximizing the weight of the munitions delivered to the target for any given period of time, thus allowing the fire mission to be completed sooner and allowing the battery to immediately relocate to a new firing position before the enemy can respond. Together with all-round armour protection and high mobility, the high rate of fire of the "Gvozdika" helped to increase its destructive effect and improve its own survival rate.


According to the technical manual for the 2S1 "Gvozdika", the maximum aimed rate of fire for direct fire is 4-5 rounds per minute. Other sources corroborate this figure and further mention that the aimed rate of indirect fire against a fixed target using an external ammunition supply was also 4-5 rounds per minute. However, when attacking different targets placed at different distances and firing upon them with different fire trajectories by varying the howitzer elevation angle, the rate of fire drops to 1.5-2 rounds per minute.


The sustained rate of fire is reported to be 1.5 to 2 rounds per minute, but this figure is not very meaningful without a further breakdown of the number of shots fired cumulatively over a specific period of time. Fortunately, the technical manual provides this information: the rate of fire with an external ammunition supply in an environment with an ambient air temperature of -10 to +10 degrees Celsius ranges from 4 rounds per minute to 1.67 rounds per minute, so the reported sustained rate of 1.5 to 2 rounds per minute is only true if it is considered the minimum rate or if the gun has been fired continuously for around an hour and is expected to continue firing. Otherwise, the "Gvozdika" can easily sustain a rate of up to 4 rounds per minute for the first ten minutes of continuous sustained fire.


Number of shots fired
Rate of fire
40 shots in 10 minutes 4 rounds per minute
50 shots in 20 minutes 2.5 rounds per minute
70 shots in 30 minutes 2.33 rounds per minute
80 shots in 40 minutes 2 rounds per minute
100 shots in 60 minutes 1.67 rounds per minute




As mentioned before, the loading assistance device is most helpful for increasing the sustained rate of fire and this can also be seen in foreign artillery systems. For example, the American 155mm M114A1 and M198 towed howitzers are reported to have a sustained rate of fire of 2 rounds per minute in the first 15 minutes and 40 rounds would be fired over a one-hour period for an average rate of just 0.67 rounds per minute, whereas the 155mm M109 self-propelled howitzer is reported to have a sustained rate of fire of 1 round per minute over a one-hour period. In other words, the average rate of fire is higher in the self-propelled system despite the fact that the loaders must operate in a crowded turret instead of an open-air environment.

With an average rate of fire of 1.67 rounds per minute over a one-hour period, the 2S1 was an excellent sustained fire weapon system. The efficient and ergonomic design of its loading assistance device can be credited for this good performance.



POWERED TRAVERSE


The 2S1 featured a basic electric powered traverse system but lacked a powered elevation drive. The motor for the turret traverse drive was installed just in front of the manual flywheel for manual turret traverse. The system was designed to allow the turret to be turned quickly but imprecisely, and the final lay must be done using the manual turret traverse drive. In terms of the overall capability, the howitzer control system of the 2S1 was not at the level of modern main battle tanks, but was modern for a self-propelled howitzer of its class for the era. Case in point, the FV433 "Abbot" was also limited to having only powered traverse, while the M108 had completely manual controls for both traverse and elevation.

Its larger cousin the 2S3 "Akatsiya" self-propelled howitzer had a fully powered traverse and elevation system controlled with a pair of control handles, like in a T-54 tank.


MANUAL CONTROLS


The image below, taken from this video, shows the two manual flywheels for turret elevation and howitzer elevation.




The manual elevation flywheel, shown below, was the only mechanism provided for elevating the howitzer.




To fire the howitzer, the gunner can either use the electric trigger button on the elevation flywheel handle or pull the trigger lever affixed to the side of the gun cradle.


D-32 (2A31) 





The Soviet 122mm caliber was an excellent compromise between the 107mm (4.2-inch) and 152mm (6-inch) calibers that combined a high destructive power against area targets and fortifications, sufficient capacity for the delivery of specialty payloads, good ballistic performance, and a practical size for more advanced fuzing options. It was also the smallest howitzer caliber in the artillery branch of the Soviet Army. The 122mm caliber was first introduced to the Russian arsenal in 1909 when Imperial Russia contracted the development of new howitzers from the German Krupp concern and the French Schneider concern, leading to the adoption of the M1909 and M1910 howitzers designed by the two respective companies. Both howitzers were almost the same in their tactical-technical characteristics and both shared the same 4.8-inch caliber. At the time, the caliber was denoted in the "line" unit, each line being a tenth of an inch. The 122mm caliber was 48 lines, or 4.8 inches. This caliber was chosen as a result of a number of analyses commissioned after the Russo-Japanese war, the conclusions of which indicated that this caliber was necessary to defeat field fortifications and structures. When the



During the 1960's and for the rest of the Cold War, the 122mm caliber had no direct counterpart in the West as NATO had standardized on the French 105mm and 155mm calibers, although there was no real effort to standardize on a unified cartridge design. In the context of an international market, the 122mm caliber was an intermediary caliber between the two NATO artillery calibers, but for the Soviet Army, it was the smallest howitzer caliber second to the 152mm although they used field guns in calibers from 100mm (BS-3) to 130mm (M-46).

The total length of the barrel is 4,270mm, or 35 calibers. This places the D-32 well above the threshold of 30 calibers that distinguishes it as a long-barreled howitzer as opposed to a short-barreled howitzer with a barrel length of less than 30 calibers like the M-30 (22.7 calibers). The mass of the barrel was 955 kg. The rifling consists of 36 grooves and lands with a progressive twist from 3°57 ′ to 7°10′. The height of the bore axis from ground level was 1,890mm.

The recoiling mass of the D-32 howitzer is 1,440 kg. This figure represents the howitzer itself and excludes its cradle and the loading assistance device attached to the immobile recoil guard, which is fixed to the cradle.

Like all other Soviet artillery systems of the time, the firing mechanism of the D-32 was electric with a mechanical striker as a backup.


The howitzer has a semi-automatic vertically sliding breech block, similar to the original D-30 breech block but not identical. This is unlike most Soviet tank guns produced since the end of the Great Patriotic War which had horizontally sliding breech blocks in order to facilitate the loader's work given the relatively small range of elevation angles that were permissible with tank guns. According to Soviet engineering manuals, if the bore axis of a tank cannon from the floor of the fighting compartment is lower than 950-1,000mm, a vertically sliding breech should be used, but if the bore axis is higher than that, a horizontally sliding breech should be used. The reason for this is because the convenience of ramming a shell into the chamber changes depends on the height of the bore axis in relation to the height of the average loader (170 cm). If the height of the bore axis is 950-1,000mm or more, the chamber will be above the elbow level of a standing man, so a horizontally sliding breech is more convenient for the loader when inserting a cartridge into the breech and ramming it in. However, if the bore axis is lower than 950-1,000mm, a breech assembly with a vertically sliding breech block is more convenient for the loader.

Howitzers like the D-32 are most often fired at high elevation angles and are only occasionally used in a direct fire role. When the howitzer barrel is raised to a high elevation angle, the breech assembly is lowered so that the height of the bore will be quite close to the fighting compartment floor, and because of this, a vertically sliding breech block is preferable over any other type.




The recoil mechanism of the D-32 included a hydraulic recoil brake with a pneumatic recuperator, filled with either nitrogen or air. These two components were installed above the breech assembly in the same layout as the D-30 howitzer, but with some modifications.

To accommodate a large elevation angle, the howitzer cradle incorporates a large toothed arc underneath the trunnion pin which interfaces with the worm drive gear of the manual elevation mechanism. This can be seen in the drawings below. The center of gravity of the howitzer is exactly centered on the axis of the trunnion so that it is well-balanced.




The 2A31 could be depressed by -3 degrees and elevated by +70 degrees, making it a gun-howitzer rather than a pure howitzer, even though the weapon itself and the D-30 it is based on are both designated as howitzers in the Soviet Union. The gun depression limit of -3 degrees is normal for a self-propelled howitzer, but it is less than the -7 degrees limit of the towed D-30. Nevertheless, it should not pose any serious issues even when the vehicle is used for direct fire against point targets such as tanks unless it is deployed improperly. The photo on the left below is by Neschevo.




The trunnion pins of the gun cradle are coaxial to the gun bore, of course, as the drawing below shows.




Unlike tank guns that needed much more compact recoil systems in order to fit entirely inside a tank turret, the 2A31 could have the large buffer and recuperator cylinders of its recoil mechanism protruding far outside the turret as it was only necessary to provide protection from bullets and shell splinters. This was easily achieved with an armoured cowling of a similar design to the one on the D-30.


Unlike the D-30, the D-32 howitzer used a double baffle muzzle brake. The original D-30 had a slotted muzzle brake with five slots. In 1978, the D-30A model replaced the D-30 and one of the primary differences was the replacement of the original muzzle brake with a double baffle design, very similar to the one used on the D-32. The efficiency of the double baffle brake was less than the slotted type, translating to a more modest reduction in recoil force. For the towed D-30A, the replacement of the original muzzle brake with a less efficient type was because the original slotted brake worked by ejecting a large amount of propellant gasses backwards to counteract the recoil force experienced by the howitzer, which was undesirable because these gasses were ejected towards the howitzer crew thus raising the overpressure of the muzzle blast excessively. However, there was no real reason for the D-32 to have differed from the D-30 in this regard because the crew was fully enclosed inside the turret and would have been shielded from the muzzle blast.




The distinctive fireballs ejected sideways from the double baffle muzzle brake of the D-32 can be appreciated in the photo below.




Of course, the muzzle brake can be removed, but a full charge cannot be used in the 2A31 without a muzzle brake installed as the recoil force will overload the recoil mechanism. Nevertheless, the muzzle brake should always be installed regardless of the propellant charge used in the howitzer.




One imperfection of the D-32 was its inability to use bagged propellant charges. This issue was partly solved by the D-16 which was originally designed to solve the issue of excessive gas contamination from the early prototypes of the D-32, but it was decided that the D-16 did not provide a significant advantage over the D-32 to be worth pursuing further. With the suspension of further work on this improved howitzer, it was decided that full metal casings with improved obturation would continue to be used as this effectively solved the issue of gas contamination. It is not known why semi-combustible propellant charges were not considered as an alternative option. This technology was already in widespread use in the form of 122mm ammunition of the D-25T and M62-T2, 115mm ammunition for the D-68, and 125mm ammunition of the D-81T.

Although this does not seem to be a significant issue, the cost of producing and transporting metal cases accumulates over time and can become problematic in a protracted large scale conventional conflict, especially for the Soviet Army with its strong focus on artillery. According to data provided by Russian historian Isaev Alexey, during the four years of the Great Patriotic War, the Red Army expended artillery and gun shells at a gargantuan rate yet they were still outpaced by the Germans and Americans by a significant margin, particularly the Americans whose industrial capacity allowed them to produce colossal volumes of ammunition in short periods of time. This was despite the fact that the Red Army's ammunition production capability had been supplemented by valuable American machine tools and shipments of explosives.

If metal cases for propellant charges could be omitted without compromising the performance of the artillery piece, then it was advisable to do so. Nevertheless, it is worth noting that metal cases for two-part ammunition can be easily reused multiple times because there is no need to mate the case to a projectile, and it is particularly easy to reload cased propellant charges for 122mm artillery rounds because the propellant is held separately in fabric bags of which there are seven, each of equal mass.



The travel lock for the 2A31 is installed on the roof of the hull, next to the driver's station. The travel lock is remotely controlled from the commander's station. To use it, the howitzer should be kept elevated until the travel lock has been fully erected by its electric motor, and then the howitzer barrel is aligned to the 12 o'clock position and depressed until it is seated properly. The remotely-controlled travel lock clamp is then closed over the barrel.


One of the staple techniques of boresighting the D-32 in field conditions is to tie two pieces of string into a cross shape around the muzzle. The muzzle brake of the D-32 does not have cross-shaped cuts for this purpose like the 125mm D-81T tank gun, but fixed nubs are provided for tying the string. The howitzer and the direct and panoramic sights are zeroed by aiming the barrel of the howitzer at a landmark at a distance of no less than 1,000 meters and then calibrating the sight until the point of aim in the sights aligns with the point of aim of the howitzer barrel. This ensures that horizontal parallax does not contribute to the dispersion of shots at long range.




AMMUNITION



Being a self-propelled howitzer, the flexibility of the "Gvozdika" as a combat vehicle was reflected by a diverse selection of ammunition types. All of its ammunition could be used in either direct or indirect fire, but of course, anti-tank ammunition was ineffectual unless used exclusively for direct fire.

A basic combat load consisted of 35 HE-Frag rounds and 5 HEAT rounds, but in practice, the combat loadout was adjusted with various ammunition types to suit the tactical situation. Regardless of the number of specialty ammunition types carried in the "Gvozdika", the number of HEAT rounds did not change.

HE-Frag


The "Gvozdika" mainly carried high-explosive fragmentation (HE-Frag) shells as it was an extremely cheap, highly versatile, reliable and lethal type of ordnance. Various models of HE-Frag rounds were used throughout the service career of the "Gvozdika", but it is particularly interesting to note that, like the D-30, it was mainly supplied with OF-462 shells that were first created for the M-30 short-barreled howitzer.


A number of fuzes were available for the HE-Frag shells supplied to the 2S1, but variable-delay point-detonating fuzes were the most common type and the RGM was the common model that operated on this principle. The V-90 was another option.

To use the shells in the "Frag" mode, the fuze is left in the superquick setting and the fuze cap is removed. The shell detonates instantly upon impacting any surface, regardless of whether it is a body of water, a marsh, or snow, thus producing the maximum fragmentation effect on targets standing on top of the surface. The sensitivity of the fuze also allows it to detonate when impacting the canopy of trees, thus allowing the shell to burst above hidden infantry. It was not permitted to fire shells in this fuze setting under conditions of heavy rain or hail as the fuze is sensitive enough to potentially detonate before reaching the target.

If nothing is done prior to firing the shell, meaning that the fuze is left in the superquick setting and the fuze cap is left on, the shell behaves as a "HE-Frag" shell. The fuze detonates after a delay of 0.027 seconds and produces a combined high-explosive and fragmentation effect. This setting provides a reasonable compromise between the two modes of destruction, allowing field fortifications to be destroyed with near misses while also producing a fragmentation effect to deal with soft-skinned targets standing in the open. If the fuze cap is left on but the fuze is set to the delayed setting, the shell behaves as a "HE" shell. It is detonated after a much longer delay of 0.063 seconds after impact. This enables the shell to explode after penetrating the earth down to an optimal depth, thus displacing the largest possible volume of soil and delivering the maximum shock effect to enemy fortifications which tend to be below ground level by nature. For example, a trench can be destroyed by firing a HE shell at a point just in front of the trench. The shell penetrates the earth at an oblique angle and explodes just next to the wall of the trench (a lucky shot may even explode inside the trench itself), thus demolishing it and killing anyone in the way. Setting the fuze is done by the loader using a special key, but it is the commander who dictates which setting is most suitable for the target.


According to the technical manual for the 2S1 "Gvozdika", the technical dispersion of HE-Frag rounds in direct fire at 1,000 meters is less than 0.2 meters in both the horizontal and vertical planes.

When firing at area targets, the direct fire dispersion characteristics are not directly applicable as the drawing below illustrates. While an elliptical dispersion pattern is maintained, the area of the impact zone increases enormously because of the additional factor of distance, which is absent when firing at an upright target placed perpendicular to the ground. Vertical dispersion becomes dispersion in depth, and horizontal dispersion becomes dispersion in width, but the impact area is only elongated in depth and not in width because of distance. At the maximum firing range of 15,200 meters, the mean dispersion of the shells in depth is 32 meters, and the mean dispersion of the shells in width is 10.86 meters. This elliptical zone with an area of 1,092 square meters is where 50% of the shells will land.




By adjusting the muzzle velocity, different trajectories could be generated.




To adjust the muzzle velocity of the shells for generating various firing trajectories, the number of propellant charges could be manually adjusted by the loader. Seven propellant bags were contained in each charge housed in a steel casing.





OF-462, OF-462Zh



The projectile weighs 21.76 kg and it contains a 3.675 Trotyl charge. The fuze weighs 0.438 kg, so after subtracting that and the weight of the filler from the total weight of the complete projectile, the share of the explosive filler is calculated to be 20.8%.

As a 122mm HE-Frag shell, it is hardly surprising that the explosive payload was between typical NATO 105mm shells and 155mm shells in weight, but the efficiency of each OF-462 shell was higher on a shot-for-shot basis. Case in point, the ubiquitous American 105mm M1 shell had a complete projectile weight of 14.9 kg and could have a 2.3 kg filling of Comp. B or 2.18 kg of TNT when fitted with a conventional M557 point-detonating impact fuze, and the equally ubiquitous American 155mm M107 shell had a complete projectile weight of 43.2 kg could have a 6.98 kg filling of Comp B or 6.62 kg of TNT when fitted with a conventional point-detonating impact fuze. Subtracting the weight of an M557 PD fuze (0.975 kg) from the total projectile weights of these two shells, we find that the share of the explosive filler in the M1 shell is 18.56% with a TNT filler and 19.8% with a Comp. B filler. The share of the explosive filler in the M107 shell is 18.6% with a TNT filler or 19.8% with a Comp. B filler.



In the Soviet Union, "Trotyl" refers to a 70/30 tetrytol composed of a mixture of 70% Tetryl and 30% TNT. Trotyl is more powerful than TNT and slightly less powerful than tetryl, but more sensitive than TNT and less sensitive than tetryl. Cast Trotyl as found in bombs and shells has a density of 1.60 g/cu.cm, which is slightly more than the 1.58 g/cu.cm density of cast TNT. The explosive velocity of Trotyl is 7,000 m/s and the Trauzl value is 285-320 ml. For TNT, these values are 6,900 m/s and 285-305 ml respectively. According to page 8-122 of the U.S Army technical manual TM 9-1300-214 titled "Military Explosives", the brisance of cast 70/30 tetrytol is 111% that of TNT when compared with the sand test. These details should be considered when comparing Soviet Trotyl-filled tank and artillery shells with TNT-filled shells.


Mass: 21.76 kg
Explosive Charge Mass: 3.675 kg

Muzzle velocities:
Full Charge: 686 m/s
Reduced Charges: 270-565 m/s

Maximum Firing Range:
Full Charge: 15,200 meters
Reduced Charge: 12,870 meters

Maximum Pressure with Full Charge: 245.2 MPa


Its maximum range of 15.2 kilometers was good, but quite ordinary for a medium velocity howitzer. Although it was nowhere close to reaching the capabilities of the 130mm M-46 counter-battery gun, it still gave the "Gvozdika" a range advantage over 155mm guns like the towed M114 or the M126 of the M109 self-propelled howitzer, both of which had a maximum range of 14.6 kilometers, and its range easily exceeded some 105mm howitzers like the M103 of the M108 which had a maximum range of 11.5 kilometers.


When the fuze is set to the HE mode, the high explosive action of the shell produces a crater with a depth of 1.3 m and a diameter of 3.3 m in soil of medium density. This is a significantly better result than the M-30 short-barreled howitzer could obtain with the same OF-462 shell, as that could only produce a crater with a depth of 0.7 meters and a diameter of 3.0 meters under the same conditions. The difference can be attributed to the higher impact velocity of shells fired from the D-32 at all ranges. By exploding deeper in the soil, a larger portion of the explosive energy is transmitted into the ground rather than being spent in ejecting soil above the shell. This allows a greater mass of soil to be displaced and as a result, the shell is more effective at destroying trenches.   

If the shell manages to actually enter the trench, there is still a powerful destructive effect because the walls of the trench will collapse from the explosion underneath them unless they are reinforced with logs, and the blast wave kills the soldiers standing inside the trench or they are at least injured by the ejecta that is propelled out of the ground.


According to CAMD RF 81-12104-9, the 122mm HE shell fired from the M-30 howitzer penetrates 30mm of steel armour sloped at 30 degrees at 1,000 meters. The armour used had a resistance coefficient of 2,360. Based on the characteristics of the shell reported in the table (21.76 kg and muzzle velocity of 515 m/s), an OF-462 shell fired with a full charge was used. The table in the document does not mention the nature of the interaction between the shell and the armour plate, but given the large thickness of the armour plate, it is likely that the shell impacted the armour and the fuze was destroyed, but the shell carried enough kinetic energy to break through. The relatively thin casing of the warhead probably could not survive such an interaction and it would have disintegrated into fragments, which would combine with the fragments of the breached armour plate to destroy anything in its path.

3VOF29 (3VOF30)
3OF24



With an explosive filler weight of 3.97 kg, the share of the explosive filler in the 3OF24 shell is 22.87%. This is close to the mathematically optimal figure of 25%, and as such, 3OF24 possesses more favourable fragmentation characteristics. There may have been a further improvement in performance if the forged steel casing is made from an improved steel alloy with better fragmentation characteristics.


Projectile Mass: 21.76 kg
Explosive Charge Mass: 3.97 kg

Muzzle velocities:
Full Charge: 686 m/s
Reduced Charges: 270-565 m/s

HEAT


During the so-called Great Patriotic War, the Red Army placed a great emphasis on the dual role played by artillery, both the towed and self-propelled varieties. Weapons like the ZiS-3 and M-30 were not constrained to area bombardment with high explosive shells, but were expected to be serve as anti-tank guns if the situation called for it. For this purpose, they were provided with armour piercing shells according to their suitability. The ZiS-3 and A-19 were fairly powerful guns and thus, were supplied with AP or APBC shells and SU-76 self-propelled guns were often supplied with a small number of APCR rounds as well. Short-barreled howitzers like the M-30 had an inherently limited muzzle velocity, making it ineffective to use such ammunition as they depended on kinetic energy. As such, HEAT ammunition was used instead.

Even by the time the D-30 entered service, it was expected to fulfill a secondary anti-tank role. This expectation carried over to the 2S1 "Gvozdika". For the D-30 and the "Gvozdika", HEAT ammunition was still the only sensible anti-tank munition given the relatively low energy of the howitzer compared to high-power guns like the D-25T.

The 2S1 was supplied with fin-stabilized HEAT shells. It could also fired the spin-stabilized 3BR1 shell that was originally developed for the M-30 howitzer, but this shell was ineffective against the modern tanks of the 1960's and 1970's and it was not supplied to the 2S1.

According to the technical manual for the 2S1 "Gvozdika", the technical dispersion of HEAT rounds at 1,000 meters is less than 0.3 meters in both the horizontal and vertical planes. This is worse than the accuracy of the HE-Frag rounds and doubtlessly contributed to the relatively low maximum effective range of the 2S1 against tanks in direct fire.


3VBK12, 3VBK12
3BK6, 3BK6M





The ballistic performance of the D-32 howitzer was sufficient for direct fire purposes against point targets, but it was considerably worse than the 122mm mod. 1931/37 field gun due to its lower muzzle velocity. As such, the "point blank" range, otherwise known as the grazing shot or direct shot range, was considerably shorter. The point blank range for a target with a height of 2.0 meters (representing an armoured personnel carrier) was 780 meters, 870 meters for a 2.5-meter target, and 940 meters for a 3.0-meter target (heavy tank). Of course, the natural vertical dispersion of the shot makes it necessary to estimate the range with some precision to have any real chance of scoring a hit at such ranges. This level of performance was quite ordinary for howitzers. The shell has a filling of A-IX-1 explosive compound.

For direct fire using the BK6(M) round, the "БК" (HEAT) range scale was provided. A tracer was installed at the base of the stabilizer fin assembly for fire correction purposes.


Projectile Mass: 21.56 kg
Explosive Charge Mass: 2.159 kg


3VBK9, 3VBK9M
3BK13, 3BK13M




The 3BK13 shell was a modern HEAT shell that entered service at around the same time as the 2S1, replacing the older 3BK6 that was primarily supplied to the D-30. The main distinguishing feature is the replacement of the conventional aerodynamic fairing of the projectile with a spike tip. In terms of performance, the 3BK13 mainly differed in having a significantly higher armour penetration power. As usual, the 3BK13 had a steel liner and 3BK13M had a copper liner. The maximum effective range was rated to be 1,500 meters.




Despite the higher muzzle velocity of 726 m/s, the BK13(M) round did not have a flatter trajectory than the BK6(M) round it replaced due to the higher drag of its spike tip projectile design. In fact, its ballistic trajectory was almost identical up to a range of 940 meters.

The shell had a filler of A-IX-1.


Muzzle velocity: 726 m/s

Projectile Mass: 18.2 kg
Explosive Charge Mass: 1.698 kg




PROTECTION


The protection of artillery batteries was considered to be a crucial aspect in conventional warfare in the Soviet Army. There was a general understanding that there were more challenges to overcome than ever before, . Soviet officers, analysts and scientists rated enemy artillery as the foremost threat to their own. The second most serious threat was aircraft, including fixed-wing high performance aircraft as well as rotary aircraft. Third on the list of perceived threats to artillery were enemy
tanks, airborne and small infantry units. Of these, enemy tanks were thought to pose the greatest threat to artillery. This type of threat was considered

When the MT-L prime mover was being designed, the need for better protection led to the Army's insistence on having armour on the new vehicle, resulting in the creation and introduction of the MT-LB into widespread service instead of the MT-L.




However, the addition of armour to prime movers was not a panacea to the serious problem of artillery protection. Enhanced mobility was considered to be the greatest countermeasure against enemy artillery fire and airstrikes. This was the primary incentive behind the decision to replace towed howitzers with a self-propelled vehicle like the 2S1, as such systems enjoyed a considerable improvement in survivability under adverse combat conditions.

When in transit, towed weapon systems like the D-30 were not particularly vulnerable to enemy artillery fire because the crew and ammunition were often carried inside armoured prime movers alongside the other sensitive equipment such as the optical sighting instruments. The howitzer itself had armoured shields and cowlings around sensitive components such as the recoil system, so only the rubber tyres could be considered vulnerable. Overall, the 2S1 had little advantage in protection compared to a D-30 towed by an MT-LB in this context. However, unlike a towed howitzer, the "Gvozdika" did not force its crew to disembark from their armoured carrier in order to put their howitzer into action, and they did not need to issue emergency calls to their prime movers when it became necessary to shift positions in a hurry. Consequently, a "Gvozdika" crew had a much better chance of surviving an onslaught of counter-battery fire or airstrikes compared to their less-fortunate towed counterparts. According to an article published in the well-known "Военный Вестник" (War Herald) magazine, the timeliness of abandoning a firing position before the arrival of counter-battery fire was identified as the primary condition for the survival of artillery in modern fast-paced combat.

The advantage in survivability was also maintained when both artillery systems are exposed to direct return fire. The "Gvozdika" was fully enclosed and had enough frontal armour to resist heavy machine guns even at point blank range and the sides could resist machine gun fire from a distance, whereas the D-30 had just a gun shield that offered only limited protection against machine guns, and only in a narrow frontal arc that could sparsely cover the gunner, let alone the rest of the crew.



The turret and hull of the "Gvozdika" were constructed from welded 2P grade high hardness, high strength armour steel plates with a thickness of 7mm and 14mm. 2P grade plates for this range of thicknesses have a tensile strength of around 1450-1550 MPa and a hardness of around 388-495 BHN, most likely of 450 BHN. The direct foreign equivalent of this grade of steel is MIL-DTL-46100 grade high hardness armour steel for combat vehicles and MIL-DTL-46100 is recognized by the U.S Army to be equivalent to the steel grade used on Soviet armoured personnel carriers and infantry fighting vehicles.


For the hull, two thicknesses of steel plate were used: 7mm and 15mm. The side, rear, roof and belly plates were assembled from 7mm plates. The upper glacis was also 7mm thick, but it was sloped at a very large obliquity, and the stamped steel transmission access hatch occupying a large portion of the upper glacis was also 7mm thick. The lower glacis had a thickness of 15mm. Curved 20mm plates form the front half of the turret, and the rear half - including the bustle - is built from 7mm plates that are only modestly sloped. The hull and turret have the same basic level of protection.


The author has not yet been able to acquire information on the armour rating of the 2S1 or any published details on its testing, but because the hull of the "Gvozdika" is as thinly armoured as a basic MT-LB and the turret reaches the same standard of protection, it is possible to use the MT-LB as a surrogate for the 2S1.


According to the article "Транспортер-тягач МТ-ЛБ" (Transporter-Tractor MT-LB) published in the 25th issue of the "Боевые машины мира" magazine in 2014, the frontal armour of the MT-LB hull provided immunity from 7.62x54mm B-32 armour-piercing bullets in a frontal arc of 150 degrees at a range of 250 meters, meaning that the side armour was immune to this bullet at 250 meters at a side angle of 75 degrees where the impact angle of the bullet against the side armour plate would be 15 degrees in a worst case scenario. Only the front of the hull guarantees immunity from this type of threat at all ranges and all angles of attack. 12.7mm caliber armour-piercing ammunition such as the .50 cal M2 AP round and the 12.7mm B-32 bullet can defeat the frontal armour from up to 500 meters because the side angle for the side hull armour would not be sufficient against such a powerful machine gun round, but the front armour itself was not vulnerable.


The front hull armour of the 2S1 consisted of an upper glacis over the engine and transmission compartment with a thickness of 7mm sloped at 73 degrees, a lower glacis with a thickness of 15mm but sloped at 37 degrees, and a plate over the driver's station with a thickness of 15mm, sloped at 40 degrees. The trim vane increased the protection of the lower glacis of the hull when it was kept in its stowed position since it is a steel sheet, but because it is of unknown thickness and unknown steel grade, its contribution was probably quite modest.

To evaluate the protection level of the front hull armour, let us compare the area with the weakest armour - the lower glacis - against a fairly common threat: the .50 caliber M2 AP bullet fired from an M2 Browning heavy machine gun. It is known that the .50 caliber M2 AP bullet pierces 0.66 inches of RHA plate sloped at 37 degrees at point blank range under the Navy Criterion, so it would appear that the lower glacis of the 2S1 is vulnerable as it is only 14mm (0.551") thick. However, considering that it is made from high hardness steel and not RHA steel, the effective thickness of the armour is actually 1.3 times higher. In actuality, the 14mm of 2P armour plate is equivalent to 18.2mm (0.716") of RHA plate. The M2 AP bullet would not be capable of reliably defeating the weakest part of the front armour of the 2S1 even at point blank range. When the trim vane is taken into consideration, it is clear that even the weakest part of the front hull armour is sufficiently protected from this threat.


The side armour of the hull was 7mm thick and completely flat. Overall, the side hull armour can only resist 7.62x54mm LPS light ball bullets with a mild steel core or 7.62x51mm M80 ball bullets with a lead core and full metal jacket from point blank range, and it was also immune from ball bullets of intermediate rifle rounds. It was completely invulnerable to 5.56mm rifles during the Cold War as only M193 light ball ammunition was available for the majority of this period until it was replaced by the M855 steel-cored round in 1983, but the steel core in M855 was made from mild steel and only served to enhance barrier penetration. The armour-piercing performance is insignificantly improved compared to M193.

However, even armour-piercing bullets of intermediate cartridges could pose a threat to the side armour. The protection from 7.62x39mm BZ steel-cored armour-piercing incendiary (AP-I) bullets fired from a standard AK-47 or AKM rifle was insufficient at close range. This particular bullet was rated to penetrate 7mm of 2P steel with a probability of 80% from a distance of 100 meters, so it could already pose a serious threat to the 2S1 from the side. Naturally, with such results it is not surprising that the side armour only offered a modicum of protection from full power 7.62mm armour-piercing rounds. The side armour is reportedly vulnerable to the 7.62mm B-32 armour-piercing bullet from a distance of 300 meters when hit at a perpendicular angle. The rear armour should only offer equal protection as the side armour as it has the same thickness, and the fact that it is tilted at 5 degrees should make no noticeable difference to its protective value as it is practically insignificant.

To protect against the .50 caliber M2 AP bullet fired from the 45-inch barrel of an M2 Browning at point blank range, the side armour of the 2S1 would have to be impacted at an incident angle of 51 degrees or more, so the side angle would have to be 39 degrees or less. This means that the frontal arc of immunity against this threat was approximately 78 degrees.


The front turret armour of the 2S1 was 20mm thick and sloped at 30 degrees. This granted it immunity from .50 caliber armour piercing bullets even at point blank range. At this angle, the .50 caliber M2 AP bullet pierces 18.6mm of RHA plate under the Navy Criterion, so it already has virtually no chance against this aspect of the turret without even considering that it is made from high hardness steel and not RHA steel. The side of the turret was noticeably more resilient than the side hull armour because of its modest slope of 23 degrees, allowing it to resist the 7.62mm B-32 armour-piercing bullet from 360 meters. The frontal arc of protection from .50 caliber armour-piercing bullets would also be larger compared to the hull thanks to the tougher side armour, but the exact magnitude of the difference is unclear.


In general, both the hull and turret have low protection against small arms and the hull is particularly vulnerable to armour-piercing bullets on the side and rear even from small caliber rifles. As such, entrenching the vehicle in camouflaged dugouts does not only improve its survivability by reducing its chances of being seen and fired upon, but the dugout itself helps to protect the vehicle by hiding the hull below ground level.




Unlike the hulls of the Object 124 and the Object 765 (BMP), the MT-LB was never designed for direct combat. For instance, the Object 124 was a self-propelled tank destroyer that was intended for deployment at the front lines where it would be much more exposed to threats from other direct fire weapons, so it was sufficiently armoured to protect against heavy machine guns and even autocannons to some extent. The BMP hull had thinner armour but was angled more sharply, allowing it to resist the same types of weapons. Case in point: the frontal arc of the hull was able to resist 23mm BZ armour-piercing shells from 500 meters.

The most vulnerable zones of the 2S1 are where ammunition is stowed. The ready racks in the turret are the most exposed, whereas the reserve racks are somewhat safer because they are lower to the ground and harder to hit, especially in a frontal attack. If the ready racks in the turret are detonated by a sufficiently powerful round, it should come as no surprise that the thin armour of the turret would be completely ripped apart by the blast.





DRIVER'S STATION




The driver of the 2S1 is isolated from the rest of the crew. The engine is installed to his right and behind him is the cooling system.

Like the MT-LB, the "Gvozdika" is steered with two tiller levers with horizontal handlebars. The instrument panel is placed in front of the driver.

He was provided with three possible methods of observation for driving. When driving around without any expectation of receiving fire, the driver opens his hatch and drives with his head peeking out as is normally done in most tracked vehicles, as shown in the photo below. If it is necessary to have all hatches closed for some reason, the driver reverts to using the windshield in front of him, and if the vehicle comes under fire, the driver closes the armoured windshield cover and navigates using his three periscopes.




To use the periscopes, the driver must first raise the protective steel shield covering the aperture windows. This is done by pushing up on a lever which connects to the shield by a pair of rods, and this rotates the shield on its hinges by a small distance so that it is clear of the periscopes.




The photo below shows the driver's periscopes and windshield both opened for viewing.




When the armoured windshield cover is locked in the open position, it acts as a visor to keep out rain and glare from the sun in the same way as the windshield covers of wheeled troop carriers like the BTR-60 and armoured cars like the BRDM.

The windshield is made of glass and it is heated. It offers a larger field of view compared to the periscopes, but its view to the right was obstructed by the hump over the transmission compartment. As such, the periscope facing the 1 o'clock direction was still necessary for the driver to see both corners of the vehicle. Additionally, the view from the windshield is somewhat constricted by the overhang of the hull so there is a relatively large dead zone in the front, and the driver does not have a good view skywards because the raised cover is in the way. Also, the front-facing periscope must be removed in order to exploit the view from the windshield as demonstrated in the photo below, or else it would block the driver's view since it is installed at the driver's eye level. Before the howitzer is fired, the windshield cover must be closed, especially if it is being used for direct fire against a target directly in the front relative to the hull.




The photo below shows the front right and front left headlights of the "Gvozdika", complete with marker lights to mark the corners of the vehicle when travelling in convoys.





MOBILITY





Besides its howitzer, one of the other main outstanding characteristics of the 2S1 was its mobility, thanks in part to the original focus on mobility as the design goal of the MT-LB chassis. Thanks to its exceptionally high mobility characteristics, the "Gvozdika" could travel almost anywhere it was required and it could be deployed in the "inaccessible" areas of a battlefield. The light weight of the vehicle greatly contributed to its high mobility characteristics as it became possible to be transported by the ubiquitous An-12 transport plane, one vehicle at a time. The larger Il-76 could carry two 2S1 vehicles at a time.

The vehicle had a combat weight of 15.7 tons, including a full load of ammunition, fuel, lubricants and other fluids, a complete set of spare parts and the crew members themselves. Naturally, the "Gvozdika" was in a completely different weight class than 152mm or 155mm self-propelled howitzers like the 2S3 "Akatsiya" and the M109, both of which weighed 27.5 tons when loaded for combat. However, it was also much lighter than 105mm self-propelled howitzers like the American M108 which weighed 21 tons, and surprisingly enough, it was even slightly lighter than the smaller British FV433 "Abbot" and French AMX-105B which weighed 16.56 tons and 17 tons respectively.

The "Gvozdika" was much heavier than an MT-LB as that weighed only 9.7 tons when combat loaded (including spare parts, machine gun ammunition and fuel, but no crew and no cargo), but it was only slightly heavier than an MT-LB towing a D-30 howitzer and loaded with crew and ammunition. An MT-LB configured for this role carried a large amount of cargo internally, increasing its combat weight to 12.2 tons, and together with the D-30 which weighed 3.2 tons together with its carriage, the total weight amounted to 15.4 tons.

The additional weight of the "Gvozdika" was compensated by supercharging the engine. Instead of the original YaMZ-238 engine that generated a maximum power of 240 hp at 2,100 rpm and maximum torque of 882 N.m at 1,500 rpm, the "Gvozdika" has a YaMZ-238N diesel engine with a power and torque output of 300 hp and N.m respectively. The engine was fundamentally the same as the basic variant used in the MT-LB. It was a V-shaped 8-cylinder four-stroke diesel with a displacement of 14.86 liters, differing only in the addition of a supercharger and the modifications thereof.

The top speed of the "Gvozdika" is 60 km/h, which is the same as the MT-LB. Officially, the average speed on a paved road is 45 km/h and the average speed when driving on a dirt road is 26-32 km/h. Compared to a D-30 howitzer towed by an MT-LB, the 2S1 does not have an advantage when travelling on paved roads but it was substantially more mobile when moving off-road. The issue was not speed since the D-30 itself had a perfectly serviceable maximum towing speed of 60 km/h with the foam-filled rubber tyres of its carriage, but rather, it was the mismatch between the wheeled carriage and the tracked MT-LB. Although the MT-LB had excellent off-road driving capabilities, it was hampered by the wheeled carriage of the D-30 and the situation only improved slightly when pneumatic tyres were introduced on the newer D-30A model.

A self-propelled artillery system had a significant advantage over towed artillery in these crucial aspects. It was also possible for a self-propelled system to move immediately after completing its fire mission or at least move after receiving the initial volley of counter-battery fire, thus improving its survivability by 15% to 20% according to the article "К вопросу о живучести артиллерийскдх подразделений" (On the issue of survivability of artillery units) by I. Epifanov in the April 1976 issue of the "Военный Вестник" (War Herald) magazine.










The photo below shows a Ukrainian "Gvozdika" being serviced under field conditions. The transmission access hatch is more than large enough for a man to stand inside and work freely.




The vehicle is able to climb a hill with a slope of 35 degrees (70% grade) and negotiate a side slope of 25 degrees. Due to the long overhang of the hull in front of the track, the vehicle is only capable of surmounting a vertical obstacle with a height of 0.7 meters, but the long length of the hull allows it to cross a trench with a width of 3.0 meters.


The superior driving speed and agility of the 2S1 "Gvozdika" compared to its foreign counterparts was facilitated by the improved visibility provided for its driver. Without good visibility, it would be unsafe for heavy vehicles to be driven at high speed - even those that are relatively light like the "Gvozdika" - due to their specific handling characteristics and the braking response of such vehicles.



SUSPENSION


The "Gvozdika" has a very similar suspension as the MT-LB, differing only in having seven roadwheels instead of six. The first and last roadwheels had hydraulic shock absorbers. Like the roadwheels of the PT-76 and BMP-1, these were made from stamped steel and were hollow and as such, they contributed to the buoyancy of the vehicle.




The 2S1 had a ground clearance of 400mm when combat loaded.

The vehicle used the same RMSh tracks as the MT-LB. The width of each track link is 350mm and the pitch is 111mm. The nominal specific ground pressure of the vehicle is 0.492 kg.f/sq.cm or 48.25 kPa. This is slightly higher than the 0.46 kg.f/sq.cm ground pressure of a basic MT-LB, but the difference is nullified if it is compared to a loaded MT-LB with a full D-30 howitzer crew and ammunition. For the 2S1, this low ground pressure allows it to confidently negotiate rough terrain and it was certainly more capable of crossing difficult terrain compared to a D-30 towed by an MT-LB as the carriage of the D-30 was wheeled and its ground clearance was less than the MT-LB, so naturally, it would get bogged down even if the prime mover itself did not.

However, it should be noted that the 2S1 retained the original narrow tracks throughout its service life whereas the MT-LB was supplemented by the MT-LBV model with a modified suspension that included wider tracks with a width of 565mm. The greater weight of the wider tracks was completely offset by the increased width, giving the MT-LBV an exceptionally low nominal ground pressure of just 0.27 kg.f/sq.cm. In the USSR, this model and its derivatives were mainly used in areas where operational experience had indicated that the narrow tracks of the basic model were insufficient. Nevertheless, if the MT-LBV was used as a prime mover for a towed howitzer, it would still be limited by the wheeled carriage of the howitzer. In other words, the "Gvozdika" still retains its mobility advantage.


FUEL SYSTEM





The vehicle carries 550 liters of fuel held in six containers located in the sponsons of the hull. The two fuel tanks at the rear corners of the sponsons are placed directly behind the reserve ammunition racks containing propellant charges, and the four fuel tanks forward of this are located in the fighting compartment, just under the turret ring.

With this amount of fuel, the 2S1 had a driving range of 550 km on paved roads.


WATER OBSTACLES


Unlike the vast majority of self-propelled howitzers, the 2S1 was a fully amphibious that could swim with only minor preparation. The vehicle could swim at a top speed of just 4.5 km/h. Before swimming, the trim vane had to be erected manually by one of the crew members. When stowed, the trim vane made a modest contribution to the protection of the lower glacis of the hull.

The "Gvozdika" was rated to cross a water obstacle with a width of 300 meters with a maximum wave height of no more than 150mm and a flow speed of no more than 0.6 m/s, so in other words, the vehicle was capable of swimming across the majority of the rivers found across the entirety of Europe, but only in calm water conditions. If the current was strong, the vehicle might lack enough propulsive force to avoid being swept away. The vehicle was completely unsuitable for seaborne operations such as amphibious landings unless it was transported right up to the beach. Nevertheless, this capability was enough for the scope of the Soviet Army.




Propulsion in water was provided by the movement of the tracks, and steering was accomplished by the braking of one track or the other to allow the vehicle to pivot around the stopped track. Reverse motion was possible, but at a very low speed because the swimming aids and the design of the vehicle itself were all entirely optimized for forward movement. The high hydrodynamic resistance of the tracks allowed them to generate a relatively strong flow of water as they run, but the efficiency of propulsion is low because the track moves in a loop. The forward propulsive force generated from the rearward movement of the lower track loop is partly countered by the reverse propulsion generated by the forward movement of the upper track loop, and even though the reverse propulsive force was limited by the presence of the hull sponsons and the sprocket wheel well, the reduction in the net forward propulsive force was quite significant. To make up for this, special grilles were installed to direct the flow of water more effectively.

Swimming forward was done by driving the vehicle in the forward gears and swimming backward was done in the reverse gear. Forward propulsion was heavily aided by a pair of special hydrodynamic grilles installed behind the rear idler of the suspension and a pair of long grilles installed adjacent to the tracks above the first roadwheel and the drive sprocket. These grilles were designed so that much of the water that was displaced by the movement of the tracks was captured by the grilles and directed backwards, thus producing a forward propulsive force. The design of the rear grilles and the shape of its vanes is shown in the photo below, courtesy of Andrey Nikolaev.




As the photo shows, the grilles were slanted inwards; i.e. the rear grilles on the right track were slanted to direct the water flow towards the left and the rear grilles on the left track were slanted to direct the water flow towards the right. This was designed so that when the vehicle was steered in the water, the turning force would be increased. For example, when turning left in the water, the left track was braked while the right track continued to run, and the grilles behind the right track increased the turning force for the vehicle to pivot around the stopped track.

These rear grilles were normally stowed by folding them up flush against the rear hull surface and then holding it in place with a swinging latch. To release it, a crew member exits the vehicle and taps the latch with a mallet until the grille is freed.

The two photos below show the front grilles. Note that the vanes curved in such a way that water is only expelled backwards. The photo on the left below is by Andrey Nikolaev.




Rearward motion in water is not supported by these special grilles. Instead, it is achieved with only the hydrodynamic interaction of the tracks with the water. Hence, the vehicle handles poorly in reverse and cannot turn easily. Maneuvering in the water is mainly done with forward motion. When not in use, the front grilles are stowed on the rear of the turret bustle to avoid premature wear and tear, but mainly to avoid damaging them in a collision since they are relative light and flimsy.




For safety reasons, it was only permitted for 30 rounds to be carried in the vehicle when performing swimming operations. This is not because of weight reasons because the small reduction in total weight by the removal of 10 rounds of ammunition is insignificant relative to the vehicle as a whole, and it has a negligible effect on its flotation. Rather, it is required to balance the distribution of weight more equally so that the center of buoyancy is not shifted excessively to the rear because of the turret. This is because the large volume of the turret does not contribute positively to the buoyancy of the vehicle since it is not submerged so it is just more weight that must be supported by the hull alone, and the turret and ammunition of the "Gvozdika" are all concentrated at the rear of the hull.

Reserve buoyancy is the amount of watertight volume above the waterline when the vessel is submerged, and a high reserve buoyancy begets a high resistance to water intake and thus, a higher level of safety in rough waters. According to Russian military historian A.V. Karpenko, the "Gvozdika" was designed with a 20% reserve buoyancy margin when combat-loaded, or in other words, 20% of the volume in the "Gvozdika" hull is above the waterline when the vehicle is afloat. For comparison, the MT-LB had a 36% reserve buoyancy margin when fully loaded for combat but without cargo and 22.5% when two tons of cargo is carried, so evidently, the buoyancy characteristics of the "Gvozdika" were slightly worse than a fully loaded MT-LB.

The small amount of water that enters the hull through the imperfect hatch seals or through small gaps in the joints between plates will be removed by a bilge pump. The bilge pump is particularly helpful if the hull armour is perforated by enemy fire, as the vehicle could otherwise take on water at an excessive rate.