IS-4 Report

 "To comrade I.V. Stalin

RE: experimental heavy tank designed at the Kirov factory

We report that the Kirov factory has designed a new heavy tank that has several distinct features from existing tanks:

• The upper front hull armour of this tank is rolled. The upper front plate is 120 mm thick at an angle of 61 degrees. The lower front plate is 160 mm thick at an angle of 29 degrees, compred to the cast 120/100/60 mm of armour of the IS tank.
• The side of the new tank is 160 mm thick and made of rolled steel, compared to the IS tank's 90 mm thick rolled steel side.
• The cast turret of the new tank is 160 mm thick, compared to the 100 mm thick turret of the IS tank.
• The new tank has a more powerful 800-850 hp engine (a prototype was built at the Kirov factory but had not yet gone through trials).
• The new tank has a planetary or semi-planetary transmission that will make controlling the tank easier.
• The new tank has a new cooling system with two fans instead of one.

The estimated weight of the new tank is 55-56 tons, compared to 45.5-46 tons of the IS tank.

Considering that the Kirov factory's tank presents an interest for further development of armoured vehicles, we ask you to give permission to the Kirov factory to build two prototypes in April of this year and perform factory trials, as well as produce a hull for penetration trials.

In order to ensure that the development and production of the new tank at the Kirov factory does not interfere with mass production and further improvement of tanks and SPGs, we ask permission to organize a special group of designers and technologists selected from the main design and technology bureau to work on the new tank. Presently, the main design and technology bureau at the Kirov factory is tasked with further improving quality of production and the design of the IS tanks and SPGs.

We ask you to approve the attached draft decree.

L. Beria

V. Malyshev

Ya. Fedorenko

April 8th, 1944"

RGASPI F.644 Op.2 D.305 L.147-148