In late 1943, Kliment Voroshilov, who had the honour of having the heavy tanks named after him, fell from political favour. Although a close personal friend of Stalin and a model party member, his incompetence knew no bounds, so the new line of heavy tanks was named after Stalin himself. The new tank was completely redesigned, with a different purpose in mind. The Red Army was beginning to go on the offensive, so the new tank was to have its armour concentrated at the front for a breakthrough role. The tank was armed with the 85mm D5T tank gun, the same as on the T-34-85, and the turret was a very similar design, though wider in the back to accommodate a ball-mounted machine gun. The turrets and guns for the new tanks were ready in time for deployment, but the hulls were not, so the first few turrets were installed on modified KV-1S hulls, resulting in the stop-gap KV-85.
The KV-7 was an experimental self-propelled gun built on a KV-1 hull in 1941, with two 45mm cannons flanking a central 76,2mm cannon in a fixed casemate. Its performance was unsatisfactory, leading to the development of the KV-7-2, also known as U-14, which replaced the two 45mm cannons with a second 76,2mm cannon. Its performance was also unsatisfactory, so the designers shrugged their shoulders and put the biggest gun they could think of in the next prototype, which ultimately led to the development of the SU-152.
Like its predecessor, the KV-5 was intended to be a super-heavy tank with the 107mm ZiS-6 cannon as its main weapon. Unlike the KV-4, however, only one design is known to exist, although tank enthusiasts today are known to draw up some odd variants, replacing the 107mm cannon with a 122mm D-25T or 152,4mm ML-20S. The actual KV-5 was designed well before either gun was fitted to an AFV, and was meant to be a balance between a fortress tank and super-heavy assault tank, heavily armoured on all sides, but particularly well-protected from the front. The 107mm cannon would have been able to knock out any German tank well out of range of any German tank gun, with the possible exception of the Tiger I, while the machine gun turrets would sweep round the tank and protect it from infantry armed with anti-tank weapons. Note that the secondary turret on top of the main turret partially obstructs the view from the commander’s cuppola, which is why the commander has a rotating periscope as well.
After Object 223 was finalised as the design for the KV-3, the 107mm ZiS-6 cannon was made a requirement for the main weapon of a new super-heavy tank to be produced as the KV-4. Twenty-seven different designs were submitted for the project, some very similar to each other, while others were radically different from any tank yet built, Soviet or otherwise. Among the designers to submit a proposal for the KV-4 project was Nikolai Fëdorovich Shashmurin, who had already worked on both the SMK and KV-1. Shashmurin showed his apparent preference for the SMK in his KV-4 design, Object 901, which was one of the largest submitted (but far from the heaviest), with nine pairs of road wheels supporting 92 tonnes. According to Shashmurin’s own memoirs, his design was ultimately selected for the KV-4 project, in spite of other designers deriding it as a glorified self-propelled gun. However, regardless of which design was selected, the KV-4 project was cancelled when the Wehrmacht attacked Leningrad, and no prototype was ever constructed.
You can see more information about all the designs submitted here. This is a Russian Wikipedia link, and while there is an English page titled “KV-4,” it shows only the drawings, and does not contain any of the information that the Russian page does.
Unknown № 1
Project Dukhov (the KV-4 as it currently appears in World of Tanks)
Project Kuzmin, et al (known as KTTS in World of Tanks)
Even before the KV-1 entered combat against the Wehrmacht, there were noticeable problems with it, and replacements were drawn up in 1940, beginning with Object 150, which was nothing more than a KV-1 with a commander’s cuppola.
The next project to be drawn up was Object 220, which had more of everything. It blimped to an enormous size, with the chassis now long enough that it mounted seven pairs of road wheels, though it could easily fit eight. The turret was shaped like that of the KV-2, though not as tall, and mounted an 85mm gun. A secondary machine gun turret was also mounted on top of the main turret, which the Soviets had already experimented with on the T-100. Because of the great size of Object 220, it was clear that it could mount a much larger main weapon, with fairly minor changes. Thus, not only was it a basis for the KV-3, but also a template for many of the KV-4 projects.
After the successful tests of the 107mm ZiS-6 cannon on the KV-2, several new heavy and super-heavy tanks were designed around it. The KV-3 was the first of such designs to be built, but the 107mm was not a requirement for it. Three designs were submitted for the KV-3 project, all based on the long chassis of Object 220: Objects 221, 222, and 223. The latter was chosen, using a sloped, elliptical turret with commander’s cuppola and armed with the 107mm cannon. A single prototype each of both Object 220 and Object 223 were constructed in 1941, but destroyed when the Wehrmacht attacked Leningrad, one of them by a direct hit from a 150mm howitzer.
The KV-2 was a largely experimental heavy artillery tank that made use of the 152,4mm M-10 howitzer in a tall turret on a KV-1 chassis. The larger turret with thicker armour added a full ten tonnes to a vehicle that was already too heavy for its outdated transmission, resulting in a tank that, although powerful and intimidating, was extremely unreliable. Much like the KV-1, the KV-2 was immune to all German guns smaller than the 88mm, and if it took advantage of a hull-down position, even that couldn’t damage it at long ranges. The KV-2 was eventually used as a test-bed for the 107mm ZiS-6 cannon, which had a higher muzzle velocity and much longer range than the 76,2mm cannon employed on the KV-1. These tests led to the development of even larger vehicles.
The Panzer 6 “Tiger” was developed in direct response to the “Russian Colossus,” the KV-1. Adolf Hitler learned from battlefield reports that towed 88mm guns were the most effective weapons against the KV-1 by far, but that KV-1 crews were wise to this, and essentially ignored all the panzers and StuGs as long as eighty-eights were present. Hitler became directly involved in German tank development at this point, and ordered that the 88mm be put on a tank. Thus the Tiger was born, officially known as the Panzerkampfwagen VI, Ausführung E, and it entered production in 1942. A heavier version, incorporating sloped armour and a longer gun, entered production in 1943, though only one was produced that year. This was the Ausf. B, also known as the King Tiger or Tiger II.
The Kliment Voroshilov tank was drawn up alongside the larger, two-turret Sergei Mironovich Kirov tank, and proved to be the favourable design, entering production in 1939. The 43-tonne heavy tank proved to be too much for German panzers to cope with during Operation Barbarossa, and German soldiers nicknamed the KV-1 the “Russian Colossus.” No panzer at the time had armament sufficient to knock out a KV-1, and towed guns had to be used instead, such as the famed 88mm. In fact, the Panzer 6, better known as the Tiger I, was developed in direct response to the KV-1. As Soviet factories began to shift tank production into high gear, the situation of numerically superior German forces against small numbers of powerful Soviet weapons was reversed.