"To the Deputy Chair of the Committee of Defense, comrade Molotov
I report that, in accordance with GOKO decree #2943ss, issued on February 24th, 1943, Kirov factory and factory #100 produced two experimental prototypes of IS tanks:
- IS-1 tank with a 76 mm gun (F-34)
- IS-2 tank with a 122 mm gun (U-11)
- IS-1 on March 22nd, 1943
- IS-2 on March 28th, 1943
As of this writing on April 3rd, the prototypes have traveled:
- IS-1: 542 km
- IS-2: 449 km
The prototype commission made the following conclusions based on the results of the first stage:
- The IS-1 and IS-2 tanks, presented for trials, meet the main tactical-technical requirements set by the GOKO.
- The tactical-technical characteristics of the IS tanks is superior to that of the KV-1S tank, due to the fortunate placement of all components.
The IS tanks presented for trials have a number of defects, the main ones of which are as follows:
- The cooling system does not allow the engine to work normally.
- The main friction clutch is weak and breaks often.
- The engine frame is insufficiently robust, which leads to it breaking.
- The balancing mechanism for the F-34 gun in the IS-1 is unfinished.
- The commission specifically noted the low quality of the diesel engines used in IS tanks. Two engines broke down during the trials.
- Components of the transmission functioned satisfactorily during trials.
- The commission deems it reasonable to:
- Continue trials of experimental IS tanks until the end of the warranty period to determine the reliability of components.
- Take all measures to immediately correct all aforementioned defects at the factory.
- Correct all defects on the 10 IS-1 and IS-2 tanks already in production at the Kirov factory, put them through warranty period trials to finalize all components and make the final decision regarding the acceptance of these tanks into service with the Red Army.
Lieutenant-General of the Tank Forces, Korobkov
Lieutenant-General of the Tank Forces, Biryukov"