Soviet post-war Object 752 and Object 777 heavy tanks were, for their time, the height of daring and originality. The designers had to strike a balance between requirements to increase armour and limits on mass. These restrictions resulted in very compact and well protected tanks with a dense, but reasonable layout. However, the era of heavy tanks was over, and these excellent designs did not move past the model stage.
Experience with the IS-4 and IS-7 turned up one unpleasant fact: no matter how perfect your tank is, a weight of over 50 tons is a one way ticket to nowhere. There were several reasons why the IS-7 did not make it into production, but its mass of almost 70 tons isn't the least important. Instead, SKB-2 and NII-100 joined forced to develop a 50-ton tank that combined the progressive solutions of the IS-4 and IS-7. This tank was indexed Object 730, the improved tank received the index IS-8, and the tank was put into production under the index T-10.
The T-10 was less protected than the IS-7 and had an inferior gun, but there weren't any unusual problems that arose when the tank was adopted to replace the IS-2 and IS-3 on December 15th, 1953.
Even while the IS-8 was undergoing trials, talk started regarding its replacement. Such an arrangement might come as a surprise to come, but there is nothing strange here. The late 1940s and the 1950s were a time of rapid development in technologies, plus the Korean War served as an additional boost for tank designers, showing that no pause in tank growth is coming.
While tanks were being built abroad to fight the IS-3 that so impressed the Western viewers of the parade in Berlin, the USSR managed to go through two generations of heavy tanks. Perhaps it would be the right move to drive a few IS-7s down Red Square and provoke the West to create armoured beasts in return, but nobody was thinking of informational warfare. The army needed real tanks.
Research of organizations like NII-48, which studied armour, encouraged a change in generations. The employees of this institute designed a series of solutions that allowed to drastically improve levels of protection without significant increase to weight. This included the "pike nose", variable thickness castings, V-shaped hulls. The T-10 looked obsolete in an instant. Yes, it had a series of novel solutions from the IS-3 and IS-7, but these were solutions from the 1940s.
The artillerymen did not sit still either. For several reasons, the IS-8 received the D-25T gun, which the military was already dissatisfied with in 1944. Additionally, Soviet intelligence carefully tracked the tanks built by potential foes, including the T43 (future M103 Heavy Tank). A successor to the IS-8 was necessary.
Work on creation of a new tank was initiated by the Ministry of Transportation Machinery in late June of 1952. SKB-2 from ChKZ under the direction of M.F. Balzhi was chosen as the developer. In February of 1953, he was replaced with P.P. Isakov. The first drafts were ready by the end of 1952, and in June of 1953, a year after being given this task, SKB-2 presented their project. Or rather projects, since at this point there were two designs. One, Object 752, was developed within the IS-3's mass range. The other, Object 777, was limited by the IS-8's mass.
From the start, SKB-2 was faced with a very difficult issue: creating a tank that, while being lighter than 50 tons, would be superior to the IS-8 in every way. Similar problems were solved before: remember the IS-3 that was significantly better protected than the IS-2. The situation repeated itself, thanks to new scientific achievements made by hull designers.
A new concept of armour was used when designing the Object 752 and Object 777, a landmark in armour technology. In these tanks, different armour plates were not only different thicknesses, but the plates themselves changed thickness. This allowed the designers to achieve unprecedented levels of armour protection while staying within mass limits.
The Object 752 was a lot more conventional than its heavier brother, but still very interesting. The dense layout resulted in the tank being only 2300 mm tall (150 mm lower than the IS-8). Recall that this is a fully fledged heavy tank. If in the West, medium tanks already approached (and in the Centurion's case, crossed) the 50 ton barrier by 1950, the Soviet classifications did not change, and the 45.3 ton tank remained a heavy.
From a technical standpoint, the Object 752 had nothing revolutionary about it. It was a classic Soviet heavy tank with six road wheels per side on a torsion bar suspension with a rear engine and hydraulic transmission. The tank was powered by an 800 hp V-12-6 engine used on the IS-8.
According to calculations, the top speed of the tank was 50 kph, with an average speed off-road of 30 kph. The suspension was interesting, as there was a proposal to use a hydraulic suspension with road wheels reminiscent of the IS-7's.
The hull design was much more interesting. The work of hull designers was already highlighted in this article, and for a good reason. Thanks to the new hull design, the Object 752 had equivalent, and in places superior, armour compared to the IS-7. The front of the hull had 215 mm of armour, more than the German Maus and E-100 tanks. Remember that this is a tank that weighed only 45.3 tons.
These mind-boggling results were achieved through the use of casting that allowed variable thickness parts to be made. The thinnest part of the upper front plate was only 90 mm thick, but it was placed at such an angle that it would only be penetrable from a nosedive. The sides were 125 mm thick, but placed at such angles that they guaranteed complete protection from the 88 mm Pak 43. The angles were reasonable enough to leave plenty of room inside for equipment, which was better than NII-100's designs, whose sloped sides often caused layout issues. The turret of the Object 752 was more conventional, and similar to the IS-8's turret. The front part was 260 mm thick, the sides 150 mm thick.
The armament was also revolutionary. The main gun was the 122 mm M-62-2T gun with a muzzle velocity of 950 m/s. This tank was the first where this gun was used. Due to the dense layout, there was no coaxial machinegun. A collapsible mount with a 14.5 mm KPVT machinegun was mounted on the roof by the loader's hatch to protect the tank from low flying aircraft.
The creators of the Object 752 included a loading mechanism. This was not a fully automatic loader, but it noticeably sped up the loading process. Despite the densely packed fighting compartment, there was room for 40 122 mm shells, 10 more than in the IS-8. There was also an alternative proposal with an almost completely automatic loading mechanism. In this case, 28 shells fit along the turret's perimeter (15 AP and 13 HE), and the loader only had to pass in the shells. Drawbacks included less ammunition and a more crowded fighting compartment.
There was an alternative armament proposal, a much more original one. Instead of an IS-8 type turret, SKB-2 designed one that resembled AMX-13 and AMX-50 turrets. The degree of influence of French projects on this design is questionable, but it's doubtful that the public demonstration of the AMX-50 in July of 1951 was ignored by Soviet intelligence.
To be fair, the two turrets only share the general concept. SKB-2 shied away from drum type canisters and only implemented a partially automated loading system, keeping the loader in place. The internal volume of the turret decreased. Interestingly enough, the oscillating turret did not have an AA machinegun, but the coaxial SG-43 machinegun returned. With this new turret, the Object 752 was only 2150 mm tall, lower than a T-26.
The heavier Object 777 was a much more revolutionary design than its brother. Judging by the presentation, this was the more promoted project. Unlike the Object 752, where the use of existing components was encouraged, the Object 777 was much more conceptual.
There were two options for the engine, liquid cooled and air cooled. Both projects, indexed V-7, were designed by the ChKZ diesel engine design bureau under the supervision of I.Ya. Trashutin. The air cooled variant was considered higher priority, as it was smaller.
To compare, the length of the IS-8's engine compartment was 3480 mm, the Object 752's was 2410 mm, and the Object 777's was only 2300 for the liquid variant and 2100 for the air cooled variant. Such a drastic reduction in length was possible due to positioning the engine perpendicularly, a first for heavy tanks. As a result, the turret could be moved closer to the center, which had a positive impact on the tank's balance and precision of shooting, especially on the move.
The engine was only one new feature of the tank. With a mass of 49,800 kg, it combined a large amount of innovative solutions. The lighter Object 752 was very low for a heavy tank, but the Object 777 was even lower. The height of the turret hatches was 2100 mm, even less than the T-64, T-72, and T-80.
Thanks to a more powerful engine (850 hp), the speed of the tank was at the level of the Object 752, but with a smoother ride. The smoothness was achieved by lengthening the suspension by one road wheel and a superior weight distribution. The tank also had several variants of hydraulic suspensions, as well as a torsion bar and hydropneumatic suspension. In addition, the tank had a planetary 7-speed gearbox.
The hull of the Object 777 was similar to the Object 752, but there were some notable changes. The maximum thickness of the UFP was reduced to 175 mm, but at a sharper angle, which reduced the weight while retaining the level of protection. As with the Object 752, the driver's seat was shifted slightly to the left. This made entering the vehicle easier and made it harder for the driver to his his head on the gun when his seat was fixed in the travel position.
The liquid and air cooled variants differed externally. The roof of the engine compartment had an air intake for the centrifugal air filter. As for the water cooled variant, it had a different shape of the rear and roof to accommodate the larger radiator.
The turret was similar to that of the Object 752, but with some changes. The front was only 195 mm thick, but due to a more extreme slope, it retained the same level of protection. The sides were 215 mm thick, making them impenetrable for the German 128 mm gun used on the Maus. The mechanical loader was not used. The Object 777 kept the coaxial SG-43 machinegun. The liquid cooled variant had the same AA mount as the Object 752, but the air cooled tank got a remote controlled AA turret on top of the main turret.
Both projects were sent to the Ministry of Transportation Machinery in June of 1953. After some discussion, the layout of the Object 777 was changed. A wooden 1:10 scale model was also made. Work on this very interesting project continued until 1954, but sadly, did not progress past models.
However, the effort did not go to waste. Solutions used in these projects went on to be used in the Object 770 tank. The shape of the hull and turret are reminiscent of its predecessor. Additionally, the experience was used to modernize the IS-8/T-10. In 1957, the T-10M entered production, armed with the 122 mm M-62 gun.
Original article by Yuri Pasholok.