IS-2 prototype at factory trials in October, 1943.
Object 240 was the factory designation for the IS-2 tank. This suggestion will use it to refer to the first prototype. Even though an 85mm gun had been chosen for the soviets next heavy tank (IS-1) in early 1943, they knew this was only a temporary measure, and design of bigger tank guns were started at the same time. This new 122mm gun was made to fit the same gun mount as that of the smaller 85mm gun. This meant that the IS-2 replaced the IS-1 in production before any IS-1’s had even seen combat.
Obviously everyone is familiar with the IS-2. A staple of the soviet tree in game, and of course a staple of WW2. But many likely do not know what makes the prototype unique, other than the muzzle brake. Initially the 122mm D-25T featured an older breech design. Which meant the operating action to close and open the breech was slower. This means that compared to the IS-2 in game, this would have an even slower rate of fire. During trials, the rate of fire achieved was only 2-3 rounds per minute (20-30s reload). Though this also included aiming and firing. I would suggest picking somewhere in the middle (2.5 rpm, 24s reload). It featured an earlier fixed magnification 2.5x gunners sight. As a prototype I would even suggest limiting its available ammunition choices down to just the BR-471 APHE and OF-471 HE. This might justify placing it at a lower BR. Since I do not think this is needed in the tech tree, I envision it as a good event or battlepass vehicle. But please leave your opinion.
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Yes
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No
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Tech tree
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Premium
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Event
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Squadron
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Battlepass
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Other
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I don’t want it
Developmental history
See history
IS-2 (object 240) development is closely tied with IS-1 (object 237) development. IS-1, which originally referred to an improved KV-13 model, but later came to refer to the tank we all know as IS-1.
The improved KV-13 model known as IS-1.
In January 1943, two Tiger Ausf.E tanks had been captured by the soviets and subsequently sent to be shot at for trials. The trials revealed that nothing less than the 85mm 52-K Anti-Air gun could reliably penetrate the front from 1000m. The improved KV-13 “IS-1” only carried a standard 76mm gun that had been used on T-34 and KV-1 tanks since the war began, which couldn’t even penetrate the front of the Tiger from point blank range. Thus the next order for the new heavy tank required it to be armed with an 85mm gun with ballistics of the 52-K.
The TsAKB design bureau had been working on an 85mm gun design since the rumours of the Tiger had appeared in later 1942. This work had led to the 85mm S-31 gun. It had the ballistics of the 52-K, however… it didn’t really fit in the turret. Blueprints showed it could be installed, but the turret would become too cramped. Expected rate of fire was just 1-2 rounds per minute, and an unacceptable drop in ammunition stowage meant this solution was canned.
The 85mm S-31 in a new turret on the improved KV-13 chassi. A tight fit.
The only way to make an 85mm fit was by increasing the turret size… which required a wider turret ring… which meant the vehicle itself had to be widened. The implication is that the design can’t just be stretched, much more work is needed. And so object 237, IS-1 was born, the enlarged version. Though the first prototype was equipped with the S-31 gun, another 85mm, the D-5T by Factory No.9, was also tested and became the one that ended up in production.
Object 237 prototype with 85mm S-31 gun.
However, back to the Tiger trials. The 85mm 52-K could reliably penetrate it, but soviet leadership obviously knew the German’s weren’t going to stop there. Thus at the same time, design requirements for a new powerful tank gun was also sent out. One gun that had performed exceptionally well against the captured Tigers were the 122mm A-19 field gun. Its first hit on the Tiger had knocked its turret off the turret ring, and blown a big chunk of armour off. The A-19 had been critized for its weight, and Factory No.9 had been working on an alternative to the A-19 called the D-2, that weighed three tonnes less (4 390kg vs 7 117kg). Though the D-2 itself never replaced the A-19 in production, it became the foundation of the 122mm tank gun. Factory No.9 combined the D-2 with the D-5 mount and created the D-25T. The name choice should be obvious.
122mm D-2 Field gun. Pictured here with a wedge breech and improved muzzle brake, not part of its original configuration.
This work was carried out during the summer of 1943, the Battle of Kursk, and appearence of the Panthers and Ferdinands didn’t start or influence the design, but it did make it a bigger priority. At the same time the IS-1 tanks were being trialled and improved. Then, the day the IS-1 was approved for production, September 4, 1943. Was also the day construction of a an IS-1 armed with the 122mm D-25T gun was approved, factory designation object 240.
The object 240 prototype was completed on the 30th of September. The first production IS-1 was still more than one month away.
Object 240 prototype with its distinctive T-shaped muzzle brake.
Though the vehicle performed much like the IS-1 in many aspects… the design of the gun wasn’t perfect. Before being installed in the vehicle, the T-shaped muzzle brake had deformed during test firing. A stronger design was being worked on, but the gun had been sent for installation in the prototype vehicle before the new muzzle brake was available. Since this information was not passed along, the muzzle brake blew up during factory trials sending shrapnel next to, and almost killing Pyotr Klimentyevich. An Army General, and son of Kliment Voroshilov. Namesake of the KV series heavy tanks. This incident thankfully did not slow down the trials by many days.
*Object 240 prototype after the second muzzle brake design had been installed, the so called “Ferdinand type” muzzle brake.
Other than the explody muzzle brake, another big issue was the extremely low rate of fire. Initially only 1-2 rpm was achieved. Even after training the crew could not achieve more than 2-3 rpm. The cause for this was an old screw breech design. This issue was known even before the prototype had been built, and a redesigned sliding breech was being developed, but it was not yet ready. Nonetheless, even with some issues, the vehicle was accepted for service on the 31st of October. The first production IS-1 had only just been built, and had yet to be sent to the army.
Production IS-2’s started being built in December. The IS-1 was being produced alongside it, but only until the year out. The improved D-25T with sliding breech began testing in January, 1944. The old screw breech version was delivered in 101 samples (previously believed to have been 145). These were all equipped with the Ferdinand type muzzle brake. The latter sliding breech design was far more common, though a few original IS-2’s did survive the war. They were however then upgraded with a sliding breech.
Production IS-2’s with Ferdinand type muzzle brake and screw breech at the ChKZ factory.
Specifications
Crew: 4
Weaponry:
122mm D-25T (screw breech / early) (Ammo: 24?)
Elevation: -3/+21
Elevation Speed: 3.5°/s
Sights:
Gunner: 10T-17: 2.5x / 28° FoV
Turret rotation: 0.6°/s* (See footnotes)
- 7.62mm DT coaxial (Ammo: )
Dimensions:
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Weight (total): 46 000kg
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Length (total): 9830mm
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Length (hull): 6770mm
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Width (total): 3070mm
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Height (total): 2430
Drivetrain:
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Engine: V-2-IS (520hp at 2000rpm) (11.3hp/t)
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Transmissison:
forward gears: 8
reverse gear: 2
- Top speed: 37km/h
Armour:
Hull:
- Front:
Upper front plate: 120mm CHA
Lower front plate: 100mm CHA
- Sides:
Upper sides: 100mm CHA - 90mm RHA
Lower sides: 90mm RHA
Turret:
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Front: 100mm CHA
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Sides: 100mm CHA
Footnotes:
See footnotes
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It was noted during trials that it took 974 rotations of the hand crank to rotate the turret the whole 360° and that it took a whole 570s to do so, resulting in a 0.6°/s traverse… It’s also noted that the turret “skipped” while rotating. Which might mean the teeth on the gears were damaged. 0.6°/s is a tenth of the speed of the Panther D turret…
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Due to unavailability of specific reports on the prototype, it’s hard to find specifications, even if they should be identical to the regular IS-2. But any help would be appreciated.
Other images
Sources: