Controversial Commander's Cupola

Three-man turrets appeared in the USSR back in the 1930s. The T-28 and T-35 tanks already had a dedicated commander. The problem was that his abilities were limited. He only had a periscope at his disposal, which had a limited field of view. The KV-1 tank that came to replace the T-28 and T-35 kept the overall layout of the fighting compartment. As before, the commander sat in the front right and had a periscope to look through. It was clear by 1940 that this was not enough. Nevertheless, it took a while for engineers to arrive at a classic commander's cupola.

The commander's cupola on the KV-1S tank appeared a full two years after the start of the KV tank family.

The first attempt to create a commander's cupola for the KV at the Kirov factory SKB-2 design bureau was made in 1940 when the T-150 tank was created. However, its cupola was not particularly successful. A more or less decent design was developed for the KV-3, but there wasn't enough time to build it in metal. The topic of a commander's cupola returned in 1942 when it was finally implemented on the KV-1S. However, the design raises a lot of questions.

The KV-13 received its commander's cupola from its cousin, the KV-13. This tank was initially developed with a two man turret, but the GABTU clearly indicated the need for a commander in May of 1942. A reworked KV-13 with a three-man turret and a commander's cupola was presented in June of 1942. This turret was never built in metal, but the cupola from the KV-1S was taken from this design.

One can only wonder how Soviet engineers all smoked the same thing, but both Nizhniy Tagil and Chelyabinsk began to produce some very strange designs. There was even a lot in common between the T-43 and KV-1S cupolas. In both cases the cupolas were cast with openings for five observation periscopes. Both were intended only to survey the battlefield and had no escape hatch.

Field of view offered by the KV-1S' observation devices. Each of the periscopes in the commander's cupola provided a 50 degree FOV horizontally and 18 degrees vertically. 

The observation cupola (factory part number 57-268) had quite a clever design. It was not as tall as the T-43 cupola thanks to its complex shape. Observation devices were housed in bulges with shutters, which protected the commander even in case of a shell hitting the periscope directly. The cast body was covered with a sheet metal cover, which changed the overall shape of the cupola. New periscopes were developed just for this cupola. They still used mirrors instead of prisms, but they were more compact than previous designs. The same periscopes were used in the hull and turret of the KV-1S and could also be found on the SU-122 and SU-85. 

Mirror periscope used in the KV-1S tank. The same periscope was used in the commander's cupola, turret roof, turret sides, and hull.

The idea of a lowered cupola was welcome, but feedback from the front lines suggests that it was far from idea. It was criticized as soon as the fall of 1942, right when the tanks began to enter service. The cupola was cramped and uncomfortable. The same thing was said at the NIBT proving grounds. It was necessary to press your head against the ceiling to use the observation devices. The cupola offered no protection for the commander's head. The view was also partially obstructed by the periscopic sight. Some commanders reported that the cupola was not being used at all.

Dimensions of the commander's cupola. The design was very compact, but required pressing the commander's head against the roof to use the periscopes.

Nevertheless, the KV-1S retained its cupola until the end of production. Even this cupola was a big step forward. Until then, the commander was almost blind. With the KV-1S he finally had vision of the flanks, and even so-so vision to the left and right trumps excellent vision forward. However, it's interesting that the SKB-2 and even the People's Commissariat of Tank Production straight up ignored critical feedback. The problems with the cupola were well known. It's not a coincidence that the KV-13 (IS-1) was developed with several types of cupolas, most of which had an escape hatch.

Original article by Yuri Pasholok.