"Commission for Government Trials according to decree of the Council of Ministers of the USSR issued on July 28th, 1948
September 4th, 1948
Kirov factory, Leningrad
To Acting Minister of Transport Machinebuilding of the USSR, comrade Yu.Ye. Maksarev
CC Acting Commander of the Amoured and Mechanized Forces, Colonel-General Solomatin
I report on the results of trials of tank #4 and its condition as of September 3rd, 1948.
On August 31st, 1948, after driving trials on a cobblestone highway, intensive leakage of oil from the engine block pressure plug due to gas penetration was discovered. When the engine was disassembled at the factory, the following was found: destruction of the piston and rings, deformation of the sixth left hand cylinder, high wear on the rings of the other pistons.
The destruction of the piston and rings took place due to working the engine at high head during trials that was permitted to occur by the cooling system in normal conditions and the general unrefined nature of the M-50T piston group.
In total tank #4 travelled for 1400 km between July 25th and August 31st, 1948. The engine worked for 84 hours 30 minutes, 16 hours 40 minutes of those without load.
During this period tank #4 showed the following issues and defects:
- The final drives had to be replaced twice due to destruction of the ball bearings of the driven first row sprocket and high wear of all other gears.
- Three internal rubber fuel tanks were replaced after cracks formed due to high heat in the engine compartment.
- The friction clutches and brakes of the shaft of the planetary gearbox and brakes quickly go out of adjustment.
- The friction clutches in the shaft assembly were replaced after they overheated on special trials. The friction clutches have small friction reserves and the pressure on the disks is high.
- The semi-rigid casing of the link between the planetary gearbox and the final drives broke as it is insufficiently robust.
- The following had to be replaced: left drive sprocket bearings, first left road wheel, rubber hoses of the water and oil systems. The rubber hoses cannot survive in the high temperatures of the engine compartment.
- The exhaust system was disassembled three times in order to correct the burning of the exhaust pipe compensators and to weld on connections of the pipes and the ejectors.
- Most teeth of the silent block connectors on the track links have been ground down. 36 track links and 17 track pins were destroyed. The track is not fully developed due to its engagement to the drive sprocket and low lifespan.
- The speedometer, electric trigger of the gun and machine guns, pneumatic reloading mechanism of the machine guns, electric drive of the gun elevation mechanism, turret traverse mechanism all went out of action several times due to production and design defects.
- The mudguards do not fully protect the driver and tank from dust and mud and are not mechanically rigid enough.
Over the trials tank #4 had to be disassembled 3 times to correct not only the aforementioned defects, but other small defects.
Presently, the tank is waiting at the factory for a new engine. An engine arrived from factory #800 and assembly will be complete on September 5-6th of this year.
In addition to the breakdown, tank #4 and the IS-7 in general has the following issues and deviations from the requirements accepted by the Council of Ministers:
- The engine temperature is at its limit. The tank can't use its top gears during the summer to avoid overheating.
- The design of the fuel tanks is poor. They burn through often and increase the danger of fire. The total fuel capacity is presently 370 L, 220 of which is used up before external tanks are used.
- The oil tank is too small and not equipped with means to heat up the oil in the winter.
- The cruising range is too small at 190 km on a dry dirt road instead of 300 km.
- The tank weighs 68 tons instead of 65 tons.
- The fuel, water, and oil systems are not developed enough for normal use of the tank in battle.
- The tools and their racks are not developed. No tools are stowed on the tank.
- The installation of machine guns is unsatisfactory. The machine guns did not pass trials. The machine gun mounts need to be redesigned.
- The electric system and communications system are not complete. The duplex radio is still not finished and has not been presented for trials.
- The exhaust system and shutters above the radiators do not protect the tank against shell splinters and hand grenades.
In addition to these main design drawbacks, there is a list of drawbacks that will be attached to the report on trials of tank #4.
Tank #3 that is being built at the Kirov factory according to the same blueprints and technical requirements is still not finished. No timeline has been established for its delivery.
Considering the above as well as the results of trials against the hull and turret as well as the situation with the vehicle overall, given the scheduled end of trials (September 15th, 1948) established by the Council of Ministers of the USSR, I consider that:
- The IS-7 tank #4 presented for government trials did not pass reliability trials and the commission cannot recommend it for acceptance into service with the Soviet Army and mass production.
- Further trials of tank #4 must be stopped and the report must be composed. Do not begin trials of tank #3, instead send it to the NIBT proving grounds for study.
- Production of 15 IS-7 tanks in 1948 based on the designs of tank #4 is pointless until the Kirov factory implements changes to the design of the IS-7 tank based on gunnery and penetration trials.
- Present 2 tanks with the requested changes for trials near Leningrad and in the South, after which the decision of accepting the IS-7 tank into production and service can be made.
I ask for your direction.
Chair of the commission, Lieutenant General of the Tank Forces, Vershinin"