Thursday 12 June 2014

IS-2 Modernization

"Conclusions on blueprings of the modernized IS tank

1. Armour protection

The front plate of the IS tank is cast from high hardness armour. The upper front plate is 100 mm thick and 60 degrees from vertical. When shot at by 75 mm gun model 1942 with muzzle velocity of 1000 m/s, or 88 mm model 1943 gun with muzzle velocity of 1000 m/s, it cannot be penetrated.
The ramming section of the hull can be penetrated with the following guns at normal:
  1. 75 mm gun model 1942 with muzzle velocity of 1000 m/s: at a range of about 900 meters.
  2. 88 mm tank, anti-tank or AA gun model 1936 with muzzle velocity of 810 m/s: at a range of 100-300 meters.
  3. From the 88 mm gun model 1943 with muzzle velocity of 1000 m/s: at about 2500 meters.
The front slope of the turret platform is 130 mm thick and cannot be penetrated with the aforementioned guns.

The front part of the turret is 130 mm thick and cast from high hardness steel and can be penetrated by the following guns:

  1. 75 mm tank gun model 1942 with muzzle velocity of 1000 m/s: at a range of 1100 meters.
  2. 88 mm tank gun model 1943 with muzzle velocity of 1000 m/s: at a range of 3000 meters.
It can be seen that the armour protection of the hull, turret platform, and turret significantly increased its shell resistance.

2. Armament installation

The gun in the modernized IS tank is mounted through the roof of the turret, for which a section of the roof is removed. The installation of a gun is simple and convenient. This method of mounting, as well as the placement of the sight in a special cast section of the turret, allowed the removal of immobile armour plates in the turret and, by removing mobile armour plates, shape the front of the turret to better resist shells.

3. Fighting compartment

The turret ring of the modernized IS tank is of the ball bearing type. A turret ring of this type provides for a freer spinning turret, and allows the removal of special turret grips, which increases the size of the fighting compartment.
The small commander's cupola with two MK-4 observation devices in the rotating hatch decrease the overall height of the tank and allow for 360 degree view for the commander.
In order to ease the opening of the hatch, a lightening device should be installed, like springs or torsion bars. The hatch should have a stopper to fix it in the open position.
An azimuth target indicator eases the commander's orientation and allows him to indicate targets.

4. Engine compartment

a) Fuel system
The fuel tanks in the modernized IS tank were moved to the engine compartment from the fighting compartment. This increased the size of the fighting compartment, and made the driver's job more comfortable. Additionally, the new fuel tanks have a reduced chance of catching fire if the tank is penetrated from the front. In place of the tanks, batteries were installed, increasing the amount of batteries from 2 to 4, which improves the electricity balance in the tank. The fuel tanks are interchangeable, which is rational in manufacture and convenient in use.

b) Cooling system
The cooling system for the diesel engine is the same as on the 701 object and Panther tank, and is located in the rear of the vehicle. Water radiators are placed near the air intake, which prevents them from being clogged with dust mixed with oil or diesel from the bottom of the engine compartment, which can occur in the production IS tank where they are near the exhaust.
The division of the air intakes between the engine system and cooling system is rational in the modernized tank, as the air taken in by the coolant system will be less polluted. It is desirable to transfer the filters from the engine compartment to the fighting compartment, which will make them easier to service and will partially aid in clearing the fighting compartment from gunpowder fumes.
In the production IS tank, the air sucked in by the fan is split into two streams, one of which cools the gearbox. On the modernized tank, the air does not cool the transmission, and overheating of the gearbox is possible, as evidenced by the trials of the partially modernized SPG at factory #100. It is necessary to modify a device (a vane wheel) to blow on the gearbox and keep the transmission temperature within acceptable bounds.
The fan case holder should be reinforced, as it could weaken, leading to a loosening of the primary drive to the fan and its breakage. 
The engine's temperature range is subject to mobility trials in the modernized tank.

5. Transmission
Main clutch
The main friction clutch of the modernized tank is reinforced. The levers have been placed inside the clutch, which made it more compact, and allowed the addition of one leading and one following disk, reinforcing it. The protection from dust is more reliable. The turning off mechanism has not been changed. As practice shows, the turning on mechanism is insufficiently protected from dust and must be improved. 
The base of the bronze cones should be increased to avoid rapid weakening of the main friction clutch on the end of the crankshaft. On the rear of the ring gear, mark a scale for the possible installation of gas distribution phases. Plan for the installation of a meter for counting divisions on the ring gear.

Chief of the 6th TU GBTU Department, Engineer-Colonel Solonin
Assistant of the Chief of the 6th TU GBTU Department, Engineer-Captain Bukatin"


  1. I thought you said the IS-2 had a 120mm upper glacis? Here it says the cast version was only 100mm

    1. Either way, it cannot be penetrated.

      I'm more interested in what the "ramming section of the hull" refers to (the lower plate?), as well as the impenetrable "the front slope of the turret platform" was, vs the front of the turret itself.

      If the "ramming section" refers to the lower hull plate, then what this says is that the lower plate is more resistant than the turret front.

  2. So did the serial IS-2 obr. 44 actually have 130mm thick turret front?

    1. Someone measured the one at the Czech museum at Lesany said the wide side was 120mm and the narrow was 80mm. But they only checked the edge. If they had a sonic device it would be better.

    2. As I earlier posted, a photo of a detached IS-2 mantlet (7th GTB, Berlin) seems to show a great thickening of the armor near the gun itself. This may be similar to the Tiger I, which had a maximum mantlet thickness > 200 mm but which wasn't representative of the whole; maybe 130 mm is something like a "weighted average".

    3. This letter is not referring to the IS-2 44', but of its "successor". The 1944 model was identical to the 1943 model in all aspects but the upper plate.

      This is a further design that changed all of the abovementioned aspects, as well as keeping the improved upper plate.

  3. The ranges given here are likely calculated for the purpose of modernization comparison and not reflective of actual performance.

    -from another soviet document:

    "Front of the hull

    The design of the front of the IS-3 hull provides superior shell resistance compared to the mass produced IS-2 hull, excluding the front sloped roof of the hull. The upper front plate protects the crew from German 88 mm shells at a distance of 100 meters or more from any angle. The upper front plate of the IS-2 (Uralmash) cannot be penetrated from a distance of only 600 meters.
    The lower front plate of the IS-3 can be penetrated by the German 88 mm gun at 300 meters at 0 degrees, and cannot be penetrated at a distance of 1700 meters. The analogous hull section on the IS-2 hull (Uralmash) protects from penetration at a distance of 5100 meters. "

    1. Yes. This is implied at the very start, although it is mispelled, "Conclusions on bluebrints of the modernized IS tank".

      This vehicle had not been built by the date this letter was written.