"To the Marshal of the Armoured Forces, comrade Fedorenko
The tactical-technical characteristics that you sent are viewed by us as a task to develop new prospective types of heavy tanks that are not yet put into practice in tank building.
As you do not have any objections regarding the requirements for the IS-6 that I approved and confirm that it is necessary to build such the IS-6 with a mechanical transmission, I consider that it is at the same possible to build a tank with an electrical transmission using the same requirements.
Development of a tank with an electrical transmission will allow us to demonstrate the advantages and specifics of this transmission compared to a mechanical transmission and determine its potential in the creation of more powerful tanks.
- The requirements for protection and equal armour from all sides are at odds with the required weight of the tank. Based on the calculations of NII-48, the following thicknesses will be required for the specified resistance:
- The installation of a 122 mm gun with a muzzle velocity of 1100 m/s will not be possible in the near future. No such gun is being produced or has been designed. The creation of such a gun will take a long time.
- Using one piece ammunition for this gun is irrational, as the mass of 45 kg (approximate) and length of 1.5 meters will create significant difficulty in loading the tank and will not allow us to achieve the rate of fire requirement (4-6 RPM).
- The creation of a 1000 hp tank engine is problematic, as there is no such engine at this time. Development and tuning of the engine will take a long time, 1.5-2 years. It is senseless to delay the creation of a new tank for this long, especially since the required mobility for this tank can be achieved with a 700-750 hp engine.
- The installation of a gun stabilizer is senseless and unprofitable:
- The rate of fire of the 122 mm gun will be limited by the reload time, not the aiming time. The application of a stabilizer will not increase the effective rate of fire.
- Calculations show that the stabilization of a 122 mm gun will require either two STP-85 gyroscopes (currently tested on the T-34-85) or one that is twice as powerful. All components of the stabilizer will be so massive that it will be difficult for the crew to work in the turret.
- The installation of two belt-fed machine guns on the fenders will increase the firepower of the tank, but the lack of ability to service them in battle (resolve jams, etc) will reduce the effectiveness, and therefore it is more rational to install one gun inside the tank.
- The specified fording depth cannot be achieved, as the tank hull will be significantly less than 2 meters in height. Equipping a heavy tank for underwater driving is a completely separate issue.
- The requirement to allow the driver to drive "without headlights" is confusing. All known night driving devices require IR emissions from the headlights. It is also worth considering that multiple trials of nighttime driving devices did not give good results and cannot be recommended for installation.
- The CO ventilation requirement is excessive.
- The requirement for a "6-8x binocular gun sight for the right eye" is unclear. Existing binocular sights, both foreign and domestic, have the same magnification for both eyes.
The NKV informs me that creating a binocular sight with different magnification for either eye is impossible and pointless. The 8x magification will also reduce the field of view and is pointless.
Thus, if the overall layout and slope of the IS-6 is preserved, the mass of the hull and turret will be at least 50-55 tons, giving a tank that weighs 75-80 tons overall instead of the 50-55 that are specified in the requirements.
Experience in battle does not confirm the requirement for equivalent all-round protection. A 75-80 ton tank will also be very difficult to transport.
The requirement for protection from HEAT shells of all calibers is unreasonable, as this will require spaced armour that will increase the weight of the tank further. The spaced armour will be destroyed by the first hit to the tank.
Based on the above, I consider that your requirements should be reworked with the incorporation of our notes.
August 8th "