Monday 12 October 2015

IS-4 Beginning

"To comrade Stalin, I.V.

On the topic of a new heavy tank designed by Kirov factory

We report that Kirov factory designed a new heavy tank, which differs from existing tanks in the following ways:
  1. Improved armour, specifically:
    1. The front of the new tank is rolled steel.
    2. The UFP is 120 mm thick, at an angle of 61 degrees.
    3. The LFP is 160 mm thick, at an angle of 29 degrees, compared to 120/100/60 on the existing IS.
    4. The side of the tank is 160 mm thick, compared to the 90 mm thick side of the IS.
    5. The new tank has a 160 mm thick cast turret, compared to the 100 mm thick cast turret of the IS.
  2. The tank has a more powerful 800-850 hp engine (an experimental design, has not yet passed trials).
  3. New planetary or semi-planetary transmission that will make controlling the tank easier.
  4. New cooling system design with two fans instead of one.
The estimated weight of the tank is 55-56 tons.

Considering that the proposed design is of interest to further development of tank production, we ask you to permit us to build two experimental prototypes of the heavy tank and perform factory trials upon completion, as well as build one hull to submit for ballistics trials.

In order for the work on the new tank to not interfere with production and improvement of existing IS tanks and SPGs, we ask for permission to form a special group of designers and technologists that will work on the tank, from the staff of the main design and technology bureau. The main objective of the Kirov factory will remain the improvement of quality and design of the IS tanks and SPGs.

We ask you to approve this project.

L. Beriya
V. Malyshev
Y. Fedorenko


Tactical-technical characteristics of the Kirov factory heavy tank:
  1. Tank type: tracked
  2. Mass: 55-56 tons
  3. Crew: 4
  4. Dimensions:
    1. Hull length: 6520 mm
    2. Length with gun forward: 9700 mm
    3. Length with gun back: 8400 mm
    4. Width: 3220 mm
    5. Height: 2445 mm
    6. Clearance: 450 mm
  5. Armour:
    1. UFP: 120 mm at 61 degrees
    2. LFP: 160 mm at 29 degrees
    3. Lower side: 160 mm
    4. Upper side: 160 mm at 22 degrees
    5. Upper rear: 120 mm at 38 degrees
    6. Middle rear: 120 mm at 32 degrees
    7. Lower rear: 120 mm at 39 degrees
    8. Cast turret: 160 degrees
  6. Armament: 
    1. 122 mm gun
    2. 7.62 mm DT machinegun
    3. 12.7 mm DShK machinegun
    4. 50 mm breech-loaded mortar
  7. Armament angles:
    1. Gun and machiengun:
      1. Horizontal: 360 degrees
      2. Vertical: +20 to -4 degrees
    2. DShK machinegun:
      1. Horziontal: 360 degrees
      2. Vertical: AA
  8. Ammunition load:
    1. 30 cannon shells
    2. 1500 DT rounds
    3. 500 DShK rounds
    4. 1000 PPSh rounds
    5. 25 hand grenades
    6. 30 mortar rounds
  9. Driving characteristics:
    1. Maximum speed: 40 kph
    2. Ground pressure: 0.86 kg/cm^2
  10. Engine power: 800-850 hp
  11. Hp/ton: 14.3-15.2"


  1. 50mm mortar? It was designed for laying smokescreen or providing ilumination?

    1. Does this mean smoke discharges on the outside of the turret or some sort of internal one? I don't think it's the former considering it's breech loaded, but perhaps I'm wrong.

    2. I'd assume it was the same kind of setup the Brits used in the Centurion (the Israelis liked that one so much the Merkavas have one too); IIRC the Soviets similarly had a light 50 mm infantry mortar as a starting point to boot.