81mm Smoke Grenades

3D6, 3D6M

For tanks built with the "Tucha" smokescreen system, 3D6 grenades were issued until the disbanding of the Soviet Army in 1991. New 3D6M grenades with a thermal obscuration capability have been offered for export. It is not known if they are used on T-72B3 tanks and other tanks that do not have the "Shtora-1" electro-optical active protection system. 

The 3D6 smoke grenade is a caseless grenade weighing 2.34 kg. It has a diameter of 81mm and a length of 220mm. The propulsion charge is located in the base of the grenade and the expanding propellant gasses exit the grenade and enter the smoke grenade launcher through twelve small vent holes around the circumference of the base and six holes on the end of the base. The grenades will travel anywhere from 200 meters to 350 meters after launch, and it takes between 7 to 12 seconds to produce a full smokescreen measuring 10 m to 30 m in width and 3 m to 10 m in height depending on various environmental factors. This does not include the time of flight which can take around 8 to 10 seconds, so the total time between the moment of launching the grenade and the formation of a full smokescreen ranges from 15 to 22 seconds. The total time taken to generate a smoke screen of the specified dimensions is 10-20 seconds. According to the manual for the 3D6, the average width of the smokescreen is 27 meters and the average height is 8 meters. The grenade generates smoke for 60 to 90 seconds, thus ensuring a very persistent smoke screen.

3D6 contains a smoke-producing compound designated P50-02-7 consisting of Hexachlorobenzene, zinc oxide and aluminium-magnesium alloy. The dark grey smoke emitted from the grenade is toxic to humans through skin absorption. The smoke is opaque to electromagnetic radiation in the visual spectrum (0.4-0.75 microns) and the near-infrared spectrum (0.75-1.4 microns). This makes it an effective barrier against active infrared imaging devices that rely on infrared illumination and it is particularly useful against laser rangefinders as the smoke will scatter the infrared laser. The spectral interference range of 3D6 is 0.4-1.56 microns. The smoke is transparent to far infrared radiation such as the 8-12 micron spectrum used by thermal imaging sights on tanks and reconnaissance systems. The smoke screen produced by 3D6 will also disrupt the infrared guidance system of wire-guided missiles and also prevent laser-homing missiles from locating the tank by scattering the laser designation beam before it reaches the tank and prevents a coherent signal from being reflected towards the missile. 

According to the specifications listed in a product page, the 3D6M grenade is launched to the same distance as 3D6 and it produces a smoke cloud of the same dimensions, but has a shorter smoke generation time of up to 60 seconds only. The total time taken to generate a smoke screen of the specified dimensions is 10-15 seconds. Due to a change in the smoke-producing compound, a white smoke with a much larger spectral interference range is produced by 3D6M. According to a product brochure, 3D6M obscures EM radiation in the 0.4-14 micron spectrum. This allows it to cover the spectrum of wavelengths used by infrared imaging devices.

The "Tucha" smoke grenade system and the accompanying 3D6 grenades were designed with a greater emphasis on using smoke for offensive purposes rather than for immediate self-defence. The grenades are aimed and fired by the gunner in the desired direction to produce a smoke screen at a large standoff distance, under which friendly forces can maneuver. Conversely, the smoke grenade launching systems of most NATO tanks are designed to generate a smokescreen at close range to screen the host tank in order to cover a hasty retreat. The response time of such a system is much quicker due to the short time of flight and air-bursting mode of detonation.

The toxicity of the smoke may make it effective as a deterrent for enemy infantry. According to a U.S Army study "Health Effects of Hexachloroethane (HC) Smoke" from 1994, high concentrations of HCE smoke were found to be capable of inducing injuries and even fatalities when unprotected soldiers were exposed for just a few minutes. It is important to note that this warning was formed based on the results of smoke tests in enclosed spaces, so it is more likely that soldiers exposed to the smoke in an open environment would only find it to be an irritant. 

3D17

The 3D17 is a more modern smoke grenade that first appeared in the early 1990's as part of the "Shtora-1" electro-optical active protection system. Its smoke is generated from the ignition of red phosphorus. The red phosphorous compound burns at a high temperature, thus allowing its smoke to block electromagnetic radiation in the 4-14 micron range, making it an effective obscurant against visual observation as well as thermal imaging devices. The smoke also completely blocks near-infrared laser beams for laser rangefinders and laser designators. Unlike 3D6, the 3D17 grenade is designed purely for self-concealment. The grenade detonates in the air just one second after launch at a distance of 50 meters from the tank, allowing it to produce a complete smoke cloud in only 3 seconds. The drawback to this is that the lingering time of a full smokescreen is only around 20 seconds, depending on environmental factors. This is enough for the tank to hastily shift its position, but little else.

Because the smoke obscures IR radiation, it can prevent the guidance system of an ATGM from tracking the position of the missile after the missile passes through the smokescreen. 3D17 may be used as a quick-acting countermeasure against guided missiles even at relatively short launching distances. For example, the time of flight of a basic TOW missile to its maximum range of 3,000 meters is 16 seconds. The crew of the tank would have enough time to deploy a smoke screen after detecting a missile launch, so that the missile operator loses visual contact with the tank and the launcher loses track of the missile. 

The 3D17 grenade has replaced the 3D6 in the Russian Army. It is used in T-72B3 tanks, and possibly older tanks that have not been modernized to a T-72B3 standard.