Friday, 8 September 2017

Failed "Laser" Tank

In the first half of the 20th century, the aircraft industry gathered up all technical and scientific achievements. Airplanes were the first to try out new materials, new engines, equipment, and armament. From time to time, tank designers had the chance to use something that was designed for aviators. The attempt to install the ShKAS aircraft machinegun on Soviet tanks in the mid-1930s was one such occurrence.

History knows many situations where attempts to combine weapons or equipment, initially designed for different branches of the army, ended up producing rather viable results. The 20 mm TNSh gun, inspired by the ShVAK 20 mm aircraft gun and installed in the T-60 tank, is one such example. It was not planned as a land weapon, but ended up in a tank in a very short amount of time.

Any machinegun designed in the USSR during the 1930s was tested for use in tanks, on aircraft, and by infantry. The ShKAS (Shpitalniy-Komaritskiy, Aircraft, Rapid-firing) was no exception. A decision was made to install this 7.62 mm machinegun into a tank. The machinegun, accepted into service in 1932, used a disintegrating metal belt, and was produced in nose, wing, and turret variants. 

ShKAS, wing variant.

Brief characteristics of the ShKAS:
  • Caliber: 7.62 mm
  • Mass: 10.62 kg
  • Rate of fire: 1800 RPM
  • Muzzle velocity: 825 m/s
  • Length from muzzle to charging handle: 935 mm
In 1935, the Main Artillery Directorate (GAU), following a request from the Main Automotive-Armoured Directorate (GABTU), worked to design a ShKAS ball mount, alter the machinegun, and install it into a T-37A tank. The result would have been a curious hybrid, a combination of three elements: an amphibious tank with an aircraft machinegun.

In 1936, there were even more plans: AA mounts with the ShKAS were planned for the T-26, T-28, T-29, BT-7, T-35, T-46, the BA-3 armoured car, armoured trains, and the STZ-3 tractor. In addition, it was planned that the ball mount for the DT machinegun in T-28 and T-35 turret would also be replaced by the ShKAS. A new "super-light tank" (no index is given in the document) and standard 45 mm gun turrets (in 1935-36, these would have been cylindrical turrets) with a coaxial ShKAS machinegun. These plans were destined to remain on paper. Trials were postponed until 1937, due to "a lack of funds", and were not revisited on such a grandiose scale.

T-37A small tank at a Kiev Special Military District exercise.

Nevertheless, the ShKAS was installed on the T-37A in time. This was the first mass produced Soviet amphibious tank, based on the experimental T-33, which, in turn, was inspired by the amphibious Vickers-Carden-Loyd M1931. The T-37A was produced in 1933-1936. 2566 vehicles were built before it was replaced by the superior T-38. The tank was crewed by two men, its top speed was 40 kph on a highway, 6 kph in water, and its range was 230 km.

The ShKAS was installed in the turret, replacing the DT, the tank's main armament. The goal of this replacement was improvement of firepower. The tank was built for reconnaissance, and it was presumed that the only combat it would see would be short skirmishes with the enemy, which would need maximum firepower, and therefore a maximum rate of fire.

ShKAS ball mount.

The ShKAS ball mount and cramped dimensions of the T-37A turret allowed it to turn 10°30' to the left and 18° to the right, independent of the turret. The turret itself could rotate 360°.

Aiming the machinegun horizontally, maximum angles.

While the horizontal range was good, the vertical range was much worse. The machinegun could aim between −4° and +22°, which created significant dead zones. It was impossible to shoot at targets too close to the tank, since the machinegun could not depress that far. This meant that enemy infantry could be located right next to the tank without being at risk of being shot by its main gun.

Aiming the machinegun vertically, maximum angles.

There were no issues with sights. The tank was equipped with two of them: an optical "PYa" sight, and a diopter sight, borrowed from the DT mount.

The machinegun was fed from a 750 round box magazine. In addition to that, 2000 rounds were kept in the tank. The full ammunition capacity of the tank totaled 2750 rounds, split into 250 round belts. Three belts were kept in the magazine that fed the machinegun, and 2000 more rounds were kept in box magazines, kept in a special rack of 7. Another box magazine was stored separately.

Ammunition rack.

Ammunition was fed through a flexible metallic sleeve, similar to the aircraft version. This device ensured that the machinegun could fire without stoppages at any horizontal or vertical angle.

The biggest difference from the aircraft version was that, on GABTU's insistence, it was converted to use a cloth belt instead of a disintegrating metal one. The reason for this was simple. It was easier to refill a cloth belt with ammunition, as there was no need to gather up the links again. In addition, there is also the risk of a link jamming something inside the tank. The loading mechanism and receiver were altered to meet this requirement.

Cloth (left) and metallic (right) ammunition belts for the ShKAS machinegun.

The turret was fixed during firing. It could be fixed in 39 different positions. During movement, the turret was locked by an additional travel lock.

Process of replacing a hot ShKAS barrel. All of this had to be done from within a cramped tank turret.

After all that, the ShKAS mount was deemed poor, for a number of reasons: poor vertical aiming angles, poor reliability of the cloth belt, which was sensitive to moisture, swelled up, and tore, as well as caused jams at a high rate of fire. Correcting these stoppages took a lot of the commander's time. The machinegun mount was difficult and uncomfortable enough to use in the cramped T-37A turret as it was. The rate of fire was also deemed excessively high; it was possible to expend all ammunition within 3-5 minutes of battle, even counting the time it took to switch magazines. Finally, the ShKAS needed special ammunition, which could not be provided for both the air force and the tank forces.

Overall view of the T-37A with a ShKAS, 1935.

Imagine a hypothetical nighttime attack of these tanks from water, firing tracer bullets. The effect on enemy morale could be higher than the tank's combat value. 1800 RPM means 30 shots per second, or 30 Hz. The human eye interprets an image as unchanging if it flashes at over 24 Hz. In other words, an illusion would be created that the tank is firing beams. The obsession with science fiction in the 1930s could have made one believe that the enemy was using ray guns, from which there was no escape, and panic would ensue. However, Soviet designers did not rely on that effect.

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