Friday, 17 December 2021

Pike for a Heavy Tank

Soviet tank building made a long leap during the Great Patriotic War, especially when it came to heavy tanks. For various reasons, Soviet medium tanks continued to use a pre-war chassis, but heavy tanks went through a revolutionary transformation. There was also competition among heavy tank designers, at times rougher than that of their German counterparts. The result of this competition was a rapid jump in development of heavy tanks. Development split into three directions by the summer of 1944. The first was ChKZ's Object 701, the second was the Object 252 (IS-6) developed at experimental factory #100. This was a grassroots initiative. Finally, the third direction was modernization of the IS-2 tank. Interestingly enough, factory #100 was tasked with a modernization of the IS-2, but after they started working on the IS-6 the task was given to ChKZ's SKB-2 design bureau.

Object 701. Its front hull was considered optimal in 1944, but penetration trials showed otherwise.

Another interesting fact is that the competitors often had similar solutions to the same problems. This included reusing previously developed solutions. The Object 701 was the result of work done by the NII-48 that had a huge effect on the development of Soviet armour. The shape of the upper front hull came from there. There were also issues, in part to do with observation. The observation port in the upper front hull didn't really help with that, but also turned out to be a vulnerable spot. Soviet designers knew about this and tried to get rid of it. The solution was only found in November of 1944.

Pike nose on the Valiant tank. For some reason, the British ignored this very good idea.

These problems were experienced by tank builders of other nations too, including the British. They developed the Valiant infantry tank that was supposed to replace the Valentine. At a mass of only 23 tons it would have 114 mm of front armour. The initial tank had a very distinctive front hull with two slopes and a periscope on the roof. For some reason, this successful solution was replaced by a strange design where the upper front hull was topped with a cast dome. Like the Valiant itself, the result was quite odd. Nevertheless, good ideas seldom stay that way, and soon something similar appeared in Chelyabinsk. Of course, Soviet designers had no idea about the Valiant, especially the early concept.

IS-2U tank model, November 1944. This tank was the first to use the "pike nose".

Factory #100 suddenly remembered their task to perform a deep modernization of the IS-2 tank. Meanwhile, ChKZ managed to develop their own variant of it, produce it, and even test it. The results of these trials showed that more work was needed, especially since there were new ideas regarding the hull. M.F. Balzhi, one of the key designers at that design bureau, also had an idea of an aerodynamic cast turret with variable armour thickness. The result was a project called "experimental prototype 701-A" and later "Kirovets-1". Balzhi was the lead engineer on this project. Factory #100 developed its own project named IS-2U around this time, in November of 1944. The lead engineer on the project was G.N. Moskvin and V.I. Tarotko was responsible for the hull. He came up with the main feature of the IS-2U: the dual sloped hull. The upper front plate was made of two halves that were joined in a V shape. The lower front plate became pentagonal and much smaller.

The Kirovets-1 had a different hull. Later, the idea with a welded section that carried the observation ports and driver's hatch migrated to the IS-4.

The Kirovets-1 had a different front hull. It was simpler than the one on the Object 701 and had a separate welded section that housed the driver's hatch and periscopes. This was an important feature, as the driver on the IS-2 had to exit through the turret. This also gave the driver the ability to drive while looking out of his hatch. The 120 mm thick plate successfully resisted the 88 mm Pak 43/41 gun in trials. However, factory #100's solution was more elegant. There was no need for a separate welded in section. The upper front plates could be 10 mm thinner thanks to the extra slope. This solution also saved a lot of metal, making the tank lighter. The Kirovets-1 weighed 47.5 tons, significantly more than the IS-2. Finally, the driver's vision would be better. The NKTP made the decision to join the two competing projects. The IS-2U contributed the front hull shape and original feature to allow the commander to control fire. The Kirovets-1 was not a dead end either, as the idea of a separate welded portion of the front armour migrated to the IS-4.

The first reworked Kirovets-1, aka IS-3. It used the upper front hull of the IS-2U tank.

There are a lot of misconceptions around the dual slope hull, otherwise known as the pike's nose. One of them claims that this joint was insufficiently robust. There are photos of a hull cracked in half along the seam between the two upper front plates that migrate from book to book. These photographs come from a report on experimental hulls produced at factory #200 (Chelyabinsk) and UZTM (Sverdlovsk). The hulls were tested against a more powerful weapon than the designers intended. The pike nose was designed to resist the 88 mm Pak 43, but the trials were carried out with the 122 mm D-25T, a much more powerful gun.

An 88 mm shell struck the welding seam directly. As you can see, it held.

122 mm sharp-tipped shells could not penetrate the front of the hull at 200 meters. One hit was made directly at the joint between the two plates, and the seam held. So where do the photos with penetrations come from? The thing is that trials were also carried out from other angles. Penetration could be achieved at 320 or 40 degrees at a range of 900 meters. Again, this was with the D-25T and sharp tipped shells. The Pak 43's penetrative power was not as impressive either against these plates or others. The lower rear plate was only penetrated at a range of 300 meters and the upper side was not penetrated even at 200 meters. Also, only the UZTM hull gave cracks. The Chelyabinsk hull performed much better, although there were still complaints.

Results of 122 mm sharp tipped shells striking the front of the IS-3's hull. No penetration.

The more important thing was that the hulls under test were different from those that were in production. The ninth prototype hull already had a different roof that was more robust than that of its predecessors. The driver's hatch in this hull was also 60 mm wider. It was built with results of the earlier trials taken into account. In other words, these photographs have little to do with the production hulls, which were considerably improved. The IS-3's hull was perfectly robust. This solution reduced the weight of the vehicle to 45,870 kg, nearly two tons lighter than the Kirovets-1.

Origins of the IS-7 visualized. Above is the improved IS-6 tank, below is the Object 257, the first IS-7 tank.

Another myth is that the IS-3 inspired another Soviet tank: the IS-7. As mentioned above, Tarotko came up with the pike nose when he was working at factory #100's design bureau. An improved variant of the IS-6 with the same front hull was developed in November of 1944. It was never built, but it became the starting point for a radically new tank, the Object 257, the first of several tanks to carry the name IS-7. This tank had a different armour layout including a V-shaped hull. These changes were caused by the desire to protect the tank from 122 mm guns with a muzzle velocity of 1000 m/s. This requirement got to the point of interfering with other aspects of the vehicle, for instance the suspension had to use bogeys rather than be individually sprung. Later Shashmurin came up with bunched torsion bars that allowed the torsion bar suspension to be used on the IS-7 again. ChKZ did not consider the pike nose to be optimal and continued to develop the IS-4 hull shape. A similar shape was used in the 65 ton Object 705 and 100 ton Object 718.

Experimental Object 730. This was the last Soviet heavy tank with a pike nose.

The pike nose made a comeback in 1949 when both the IS-4 and IS-7 were no more. Decree #701-270ss of the Council of Ministers of the USSR prohibited development and production of heavy tanks weighing over 50 tons. ChKZ's SKB-2 design bureau and the factory #100 branch in Chelyabinsk were ordered to develop a 50 ton heavy tank, essentially a tank made with IS-4 components and the size, mass, and protection of the IS-3. In practice, many solutions were taken from the Object 260, including the front hull. The resulting tank was named T-10. This was the most numerous post-war heavy tank and also the last mass produced Soviet heavy. 

The T-10 was also the last Soviet tank to use the pike nose, at least its classical variant. A new concept for heavy tank armour evolved by the early 1950s. The hulls were cast with variable thicknesses, which allowed for radical improvement in protection at the cost of very little extra weight. The first such tank was the Object 777. It remained on paper, but it was followed by Objects 277, 279 and 770. Even though they had cast hulls with variable thicknesses, Objects 277 and 279 still have something reminiscent of a pike nose. As for Soviet medium tanks, the concept never landed there. An attempt was made to introduce it in Leningrad, first to the T-22 and later on the Object 907. By the start of the 1960 even those designers fell back to the IS-4 type upper front hull or even just one monolithic upper front plate. Other methods of protection were also used.

The Object 277 heavy tank had a cast front hull that was somewhat reminiscent of the pike nose.

As you can see, the idea of the pike nose came from the Leningrad design school, but ironically the best known tank that used this solution was designed in Chelyabinsk. The unveiling of the IS-3 tank at the Victory Parade on September 7th, 1945, had a tremendous effect. The IS-3 became the gold standard for a modern tank abroad, so it's no wonder that some solutions were borrowed from it, including the pike nose. One may recall the AMX M4/AMX 50 family of tanks. This was not the only project that copied the pike nose from the IS-3. For instance, the Lorraine 40t had a similar hull, but with the AMX 50 one can see how French designers followed the same thought process as Soviet ones. AMX began with an IS-4-like upper hull. The first three prototypes had an upper front hull made from three plates. The cause was simple: there were two men in the driver's compartment. As soon as the radio operator was removed, AMX immediately introduced a pike nose. This work is dated 1950. The idea did not last for long, as the French also saw the benefits of casting. The last iteration of the AMX 50 that can be seen in Saumur today has a cast front hull that is somewhat reminiscent of the Object 277. This was not a copy, but rather convergent evolution.

Pike nose on an experimental AMX 50b. Later the French also moved to casting.

The Swedes had a similar evolution, although without the casting step. The EMIL tank used to have an upper front hull similar to the AMX 50 made up of three separate plates. The Swedes saw the IS-3 just like everyone else and realized the benefits its hull offered. The final variant of their tank known as the Krv received a pike nose. Unfortunately, even though Landsverk made a successful chassis, Bofors did not manage to build a turret or a gun for it. The Krv remained an experiment, just like the AMX 50. 

Swedish take on the pike nose concept. Landsverk did not take the easy way out and made a curved upper front plate. This made production more difficult, but there was no seam.

Nevertheless, the pike nose found a place abroad, although in a different form. The Americans adopted a similar concept in the late 1940s. As they favoured cast hulls, the upper front hull was of course cast. The assistant driver was removed and the driver now sat in the middle. This solution was similar to what was done on the IS-3. The first tank to receive this hull was the Heavy Tank T43, future Heavy Tank M103. The same solution was used on the Medium Gun Tank T48, the future M48. The FV4201 British tank developed in the late 1950s that later evolved into the Chieftain (as an aside, it was the Chieftain that was Britain's first MBT, not the Centurion like many believe). This tank also has something similar to a pike nose, although flattened in the center.

The American tank on a pike nose. The Heavy Tank T48/M103 was the first to receive this type of hull.

The pike nose is not presently in use, but that is likely temporary. History moves in cycles, and it's possible that the dual slope front hull can return someday. This solution has its upsides and downsides and should not be disregarded.

Original article by Yuri Pasholok.

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