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IS-7 model 1946 during factory trials.
I think it’s sad that the IS-7 model 1947 is practically unobtainable in game.The iconic and final version of the vehicle could’ve served as a great tech tree vehicle. The model 1946 is much less iconic as it has no surviving example, neither are there any great pictures of it, only partial ones.
The sources are not optimal. But they do they job and seem accurate enough. This is a slight revision of the post on the old forums.
The IS-7 model 1946 in game would generally be similar to the model 1947. But there are still quite some differences. The biggest visual difference is the turret, which might be considered closer to the IS-6, but on steroids. However it does posses a commanders cupola, which could be a weakspot. And due to the size, thickness and angle of the turret roof, it might be a weakspot for high explosive shells and large caliber APHE shells.
The hull sides might however be the biggest change. They would be particularly nasty, being able to stop the majority of conventional projectiles (even straight on) unless one shoots at the bottom third of the tank. Due to the increased horsepower and lower weight, it would also have significantly improved mobility (18.2hp/t vs 15.44hp/t). Though its ammunition selection might be slightly worse with the BR-482 shell that did not have a ballistic cap. The vehicle would likely be stronger than the model 1947 in game, however there are some potential weaknesses atleast.
Development history
See history
The development of the IS-7 goes back to the cancellation of the IS-6 (object 252/253). Some specifics are blurry, but regardless. In December, 1944, the IS-6 was sent for trials. Where it appeared alongside the Kirovets-1 (object 703), the tank that would become the IS-3. Though the IS-6 didn’t directly compete against it. The IS-6 was a rival to object 701 (IS-4), with the goal of creating a brand new modern heavy tank. The Kirovets-1 was merely a stopgap design intended to fix the IS-2’s most crucial issues while retaining major components. The IS-6 performed poorly in many metrics, while the Kirovets-1 stole the show. Resources were ordered to be redirected to the Kirovets-1. Work on the IS-6 didn’t stop completely, it continued until early 1945, but in practice, the project was dead. An improved version of the IS-6 had been designed in November, incorporating a piked nose design, this was the same nose design that was ordered to be incorporated into the Kirovets-1 following the trials, creating the famous IS-3 design. However, due to the state of the IS-6, the improved version was not approved for prototyping.
Blueprint of the object 252 from August, 1944. Here it is depicted with the 122mm BL-13, which never made it to the prototype
Diagram of the improved object 252. Commonly known under the made up name “object 252U”.
In February 1945, a new heavy tank project was ordered by the NKTP for the tank that would succeed the IS-4 (that was still in development). However this order only concerned ChKZ, the tank plant that designed the IS-3 and IS-4. But it is believed that LKZ (who designed the IS-6) received a similar order. Either way, LKZ at that time began designing a new heavy tank, which by no coincidence shared some design features of their failed IS-6. This project received the index object 257 by GABTU as well as being named IS-7. The design was completed in June that same year, but due to some key factors, mainly the discovery of the German Maus tank in Kummersdorf, the requirements for a new heavy tank were revised. The tank now had to possess armour that could withstand the German 128mm KwK/PaK 44. Have a power to weight ratio of 20hp/t, and carry a 130mm cannon. The 600hp V-16F engine of the 257 showed many defects in tests, even when it was downrated to 520hp. And the 257 “only” carried the 122mm BL-13 cannon. The design could not be redesigned easily, and simply had to be thrown out.
Diagram of the object 257, the first IS-7.
Straight view of the 257.
A new design was born, or perhaps designs. These were objects 258, 259, 260 and 261. These were not four completely different tanks however, broadley speaking they were the same. The differences between them were merely in their engine and transmission. The 258 had the TD-30 engine with a planetary transmission. The 259 had the same TD-30 engine but with an electromechanical transmission. The 260 had a twin V-16 engine with the planetary transmission. And the 261 had the twin V-16 and electromechanical transmission. All were drawn in two versions, one with the 130mm canon, and a second still with the 122mm BL-13. Supposedly the BL-13 was kept as an option by chief designer (Zh. Ya. Kotin), as it had some advantages over the S-26. But the fate of the BL-13 was already set in stone, only the 130mm option would be approved. The object 260 was regarded as most promising, and finalized blueprints of it were ready in September 1945.
Blueprint of the object 259 (version 1) with TD-30 engine and electromechanical transmission.
An analogue blueprint of the object 260 (version 1), showing (poorly) its twin V-16 engines and planetary transmission. Note how they are otherwise identical.
In October, 1945, a letter was sent to Beria requesting the permission to build two prototypes of this tank. During the wait, LKZ developed and tested some of the features that would appear on the object 260, as the approval letter didn’t appear until February, 1946. This letter was however personally signed by Stalin. The development of the planned engine, the twin V-16, was behind schedule, and thus the TD-30 engine was back on the menu. Although this now mirrored the plans for object 258, the project index 260 was still kept. The new S-26 cannon (now seemingly known as S-70) and the loading assist device was to be tested by installing an IS-7 (1946) turret on an IS-2 chassis in July 1946. This plan was however never realised as the S-26/S-70 cannon was only ready after the turrets had been shipped off to armour trials and for installation on the IS-7 hulls. Imagine what a War Thunder event vehicle that could’ve been! The first prototype was completed on September 8th, 1946. With the second prototype to come on Christmas day (December 25th, 1946).
A later blueprint of the object 260, from 1946. Note the revised muzzle brake.
Diagram of the IS-7 model 1946. Although it is basically identical with the blueprint above, the remote AA turret mount has been raised slightly.
The two prototypes were extensively tested the following year, several flaws were found with the design. Among them, though not exclusively, was its armour construction and the engine. Requirements for the new improved version appeared in April 1947, along with the order to deliver three prototypes of this version by September that year. The new version got a redesigned turret. The engine was switched to an M-50T, and the side armour construction was completely altered. This is the version of the tank everyone is familiar with and the one that stands in Kubinka today. The first prototype was completed already in late July, however the second and third were only completed on the 6th of October, and the final one on the 30th of December. From testing of these three prototypes, another two improved vehicles were built in 1948, with another 50 scheduled for 1949. The project ran into a myriad of issues which caused further delays. And then, February 18, 1949, the order was signed that banned the development of any armoured vehicle exceeding 50 tons in the USSR. This was the end of the IS-7.
One (model 1947) was sent to Kubinka where it is kept today. I believe that is the third prototype. One prototype burned up during trials as the automatic extinguishing system failed. The others were certainly scrapped.
IS-7 model 1947. The one you know and love.
Specifications
Crew:
- Commander
- Gunner
- Driver
- Loader
- Loader
Weaponry:
130mm S-26/S-70* (see footnotes) (Ammo: 30)
- Mechanical loading assist (6 rounds ready rack with assisted loading, 6-8 rpm)
- Elevation: -3°/+15°
- Sight:
Gunner: TSh-46B: 3.75x/7.5x with 19°/9.3° FoV
Commander: TKP-2:
Commander override: Sturm
Targeting speed: 20°/s horizontal and 3.5°/s vertical - Ammunition: Same as S-70* (see footnotes)
14.5mm KPSh (mounted on commanders cupola) (50 round box magazines) (Ammo: 300)
- Elevation: -5°/+85°
7.62mm x4 ShKAS* (see footnotes) (Ammo: 2000)
- 2x mounted coaxially
- 2x mounted in a remote controlled turret on the turret rear (400 round belt each)
Elevation over front 120°: 0°/+45°
Elevation over rear 240°: -7°/+45°
Targeting speed: 60°/s horizontal and 30°/s vertical
Dimensions:
- Weight (total): 65 922kg
- Length (total): 10 970mm
- Width (total): 3400mm
- Height (total): 2600mm
- Turret ring diameter: 2000mm
- Road wheel diameter: 710mm
Engine: TD-30 (1200hp/900kW) (18.2hp/t)
Transmission: Planetary gearbox
- 6 forward gears
- 2 reverse gears
- Top speed:55km/h* (see footnotes)
Armour:
Hull:
- Front:
Upper: 150mm at 58°H/68°V
Lower: 150mm at 50°
Driver’s roof: 45mm at 82° - Sides:
Upper: 150 at 52°
Middle: 100mm at 63°
Lower: 16mm at 63° - Rear:
Upper 70mm at 55°
Lower: 70mm at 8° - Roof:
Front: 30mm
Rear: 20mm
Turret:
- Front: 240mm at 0-45°
Mantlet: 350mm - Sides: 185-240mm at 30-45°
- Rear: 10mm at 40°
- Roof: 30mm at 84-90°
Footnotes:
See footnotes
-
The cannon intended for the IS-7 is originally called S-26, but later S-70. It seems likely the gun was originally named, or atleast called S-26 because of the cannon it was based on (S-26), but this new development of the gun intended for the IS-7 received the name S-70. Though the S-70 went through a couple of changes during these years of development and the cannon equipped in these early 1946 prototypes are not entirely identicalt to the later 1947/1948 models. Calling it S-70 seems more appropriate, but S-26 doesn’t seem wrong and would be a way to differentiate it from the later model.
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Performance of the 14.5mm KPSh machine gun is unknown, very little can be found online about it. Sources needed.
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The sources disagree about the amount of 7.62 machine guns (ShKAS) that the vehicle had. But from the pictures it is clear two were mounted coaxially. Those however are the only ones that can be easily confirmed. It seems both the ones intended to be mounted on the turret front sides and hulls sides were never installed. And it is unclear if the rear remote controlled turret was ever operational.
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The second prototype achieved the top speed of 55km/h in testing in March 1947, but the vehicle was rated for a top speed of 60km/h.
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No reverse speed is mentioned, and its transmission differed from the model 1947. However it too had two reverse gears and thus I would expect similar reverse speed.
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Some of my sources disagree with each other on some statistics, some I take as being due to rounding numbers, but others I have gone and listed the one most repeated or most believable, an example being that one source lists 500 pieces of ammunition for the 14.5mm instead of 300.
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It is unclear when the BR-482B projectile became available, and unclear overall what shells were used during prototyping of the 1946 models. Perhaps the original BR-482 that did not have a a ballistic cap were used. Further research should be done.
Other images
See images
Inspection of the front of the prototype. Notice the housing of the left coaxial 7.62 ShKAS.
Maintenance of the 14.5mm KPSh machine gun?
Engine cooling system tests.
Rear of turret.
Small scale model. Note that it features a mixture of design choices from both the early 1945 version (muzzle brake) and the later 1946 version (coaxial mg placement).
Comparison spreadsheet of KV-220, KV-3, IS-4, IS-6, IS-7 model 1946, IS-7 model 1947
Sources:
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https://zen.yandex.ru/media/yuripasholok/morda-klinom-dlia-tiajelogo-tanka-5f7eb0a715099c198a02f2f6
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Oxxxymiron is an ivory tower. Soviet heavy tank is an ivory tower
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M.V. Pavlov, I.V. Pavlov (2021) Otechestvennye Bronirovannye Mashiny 1945-1965 gg.: Chast’ 1 – Legkiye, Sredniye I Tyazhelye Tanki (Eng. National Armored Vehicles 1945-1965 Part I – Light, Medium and Heavy Tanks). (Отечественные бронированные машины 1945-65 - 0001.htm)
