Wednesday, 10 July 2013

T-50: Kirov Factory

The task to develop a new light tank for infantry support fell to two Soviet factories: factory #174, and the Kirov factory. While, ultimately, a factory #174 prototype was accepted by the Red Army, the story of the Kirov prototype is no less interesting. Despite its rejection, a small number of these tanks were built (I can find reference to two prototypes, at least), and defended the Kirov factory during the siege of Leningrad.

The Kirov T-50 is well outlined in a note written by an engineer from factory #174, complaining about it.

"From December 24th to December 27th, 1940, I, as a member of the Model Commission, participated in examining the technical project for the T-50 Kirov factory tank. As I do not agree with the conclusions of the commission regarding this project, I include my list of issues here.

Here is the list of points that make me question the judgement of the commission:
  1. The main goal of the project was not met: the weight. My suggestion on this point was declined, and the commission accepted the project, based on the fact that the main characteristics were satisfactory, and proposed that the Kirov factory should reduce the weight. Experience shows that, unless the project is radically altered, it will not be possible to meet the weight requirement in production.
  2. Despite the large amount of time provided for this project, many components are insufficiently developed and tested, even for a prototype. This is pointed out, in a somewhat nicer way, by the Model Commission. The most serious complaints have to do with the hull, gearbox, and cooling system. These issues are the most pressing. The unprotected final drive gears and vision ports are secondary issues.
  3. The analysis of the two projects (Kirov and #174) provided enough material for an objective comparison between the two, and a correct and final decision, which the commission was incapable of doing. This can be seen when comparing the two projects:
    1. The overall layout is the same. The Kirov tank is 5400 [Note: units are in millimeters] in length, while ours is 5000. The width of the Kirov hull is 1475, and ours is 1525. This obviously makes the Kirov project heavier.
    2. Hull and turret: the Kirov factory uses a turret ring with a 1500 mm wide turret ring, which is 100 mm larger than our project. This does not lead to a corresponding increase in the turret ring opening (the hull is wider by 100 mm), and this results in many organic defects in the vehicle.
      The most vulnerable turret platform armour plates are installed at an angle of 20 degrees, which leads to them being penetrated by 37-45 mm shells from 325-450 meters (compared to our project with angles of 40-50 degrees, removing the danger from these shells at any distance). The hull is heavier than the project allows.
      The turret has vertical armour angles of 15 degrees (compared to our 20 degrees), which can be penetrated from 450-500 meters. Our project has much greater weight conservation, which allows us to increase the turret armour to 45 mm and protect it from the aforementioned shells from further than 50 meters.
      The narrow hull, despite the larger turret ring, makes the vehicle very crowded. It is not possible to install a flamethrower or additional fuel tanks, and makes operating the vehicle very inconvenient.
      According to our information, the hull was not changed according to advice from the commission, which will lead to an increase in mass later. The roof above the driver, despite the correct thickness of 30 mm and the commission suggested thickness of 25 mm, is only 20 mm, which leads to a reduction in weight at the cost of robustness. 
    3. On the transmission: the Kirov gearbox has 8 gears forward, compared to the 4 gears in the project specification. In theory, this is supposed to give an improvement, but practically only leads to a 5-gear gearbox that is difficult to use. The necessary complete re-working of this component will lead to the re-working of the entire transmission. Our factory has developed several types of gearboxes (5-gear, 8-gear), as well as an experimental planetary gear one, and any one can be installed if there is a need for it.
      The Kirov project transmission is also too large, with an insufficient armouring of the reductor gears, which gives a very dangerous weak spot.
    4. On the suspension: the projects are analogous. The Kirov factory uses a layout that we use on the "126" and "T-50" tanks. Aside from this, their tank uses shock absorbers like those on the PzIII, which is undesirable, given the difficulty of their production. Our vehicle can also be stabilized by these shock absorbers, but that is not necessary, since other measures were taken.
    5. On the engine: the Kirov project uses a creative approach of using a radiator around the fan, at the air exhaust. This prototype is not supported by practical experiments, and is insufficient for this task due to how easily it gets clogged, and a high resistance. The latter is confirmed by the experience of factories #37 and #174.
      There is also insufficient space to install one of these assemblies on each side of the engine. During winter testing, these defects will likely not be detected. It is necessary to test in the summer, during hot and dusty conditions, which will lose time, and result in many modifications to the tank, which will only make it heavier.
    6. On armament: the Kirov project has a third machine gun, with no sight, stationary in the hull to the side of the driver.
      This is a completely useless item, which cannot provide any kind of accuracy, and turns a machinegun into a child's toy.
      This defect was noted by the armament subcommission (GABTU - comrade Gorohov, Gen. Staff - comrate Pribytkov), and it was suggested that it be removed. However, the commission chair comrade Korobkov suggested that it be left in, and noted only as "3rd machine gun" with no mention of its uselessness.
      Our factory's project, due to the decreased weight, can be modified with useful a 3rd machine gun that has an optical sight, which will be done.
      In other cases, the Kirov factory project requires significant reworking.
...
Chief Engineer of the #174 Voroshilov factory, Ginzburg"

As you can see, the tanks ended up being quite different, despite still being called "T-50". The book Konstruktor Boyevih Mashin, a history of the Kirov factory, points out things that Ginzburg glossed over. Namely, that the Kirov prototype was 13.8 tons (so "only" 300 kg overweight), and was capable of reaching 65 kph (compared to the #174's prototype's maximum speed of 52 kph) with its 300 hp engine. 

However, Ginzburg's complaints were legitimate, and, on April 5th, 1941, Fedorenko's decision on the matter was in favour of factory #174. He also writes about some interesting proposals from Kirov factory and factory #183:

"From the two T-50 prototypes built by factory #174, and the one prototype built by the Kirov factory, a #174 prototype is accepted.

The Kirov factory proposes that the thickness of armour be increased to 60 mm, and a 76 mm gun be added, increasing the mass of the tank to 25.5 tons, with a maximum speed of 40 kph with a 300 hp V-4 engine.
Factory #183 has investigated the T-34, and proposes that it could be built with torsion bars, which, with 45 mm thick armour, results in a 25 ton tank, and with 60 mm armour, a 28 ton tank. The armament of the tank would be a 76 mm gun, and the 600 hp V-2K engine would offer a maximum speed of 50 kph.
Comparing the two projects, it can be seen that the two tanks have the same armour and armament, at a negligible difference in weight. The T-34 has an 21.4 hp/ton, versus the T-50's 11.7 hp/ton. 
Having two tanks meant for the same purpose only makes the supply chain more complicated. The T-50, as an infantry support tank, is already being built by factory #174.
I deem it unnecessary to build a T-50 with 60 mm of armour, due to the following reasons:
  1. The T-34 with torsion bars has superior characteristics.
  2. There is no point in needlessly increasing the amount of different tank types in use.
  3. This project would distract the Kirov factory from their main tasks.
Chief of the GABTU of the Red Army, Lieutenant-General of the Tank Forces, Fedorenko."

Kirov Factory's last contribution to the T-50 project was by its chief engineer, Kotin. During a review to simplify the construction of the T-50 tank on December 1941, he suggested that the commander's cupola be removed. Factory #174 declined that modification. 

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