"Fighting compartment observation methods
The commander must have uninterrupted 360 degree vision. To achieve this, a commander's cupola was introduced for the KV-1S and then T-34.
The KV-1S commander's cupola was equipped with four mirrored periscopes, providing 360 degree view range with 22-40 meters of dead space. This cupola was unsatisfactory for the following reasons:
- Mirror periscopes were destroyed by nonpenetrating shots.
- Mirror periscopes were inconvenient to use (the commander was looking 30 degrees up), and were low in quality, distorting the image.
Because of this, a new prismatic observation device was ordered, based on the English MK-4 device.
This device was designed and produced by factory #393 in May of 1943. After trials in August, it was mass produced.
The MK-4 device provides 360 degree vision by means of rotation. A lack of rear prism allows use with little change to the observer's position. By order of GBTU KA, a commander's cupola was developed with double 360 degree vision, based on the MK-4 device.
The cupola has 6 slits, protected by armoured glass, and is covered by a rotating turret hatch, which has the MK-4 device built in. Observation may be performed through the slits or the MK-4 device.
A cupola of this type was installed on the IS tank and replaced the KV, and T-34 tank cupolas. Later, an analogous cupola was installed on the T-44 tank, with the only difference being the use of the NZP-20a observation device, providing better vertical vision range.
The difference between the IS and T-34 cupolas is the armour and glass thickness. In the former case, it is 90 mm, in the latter, 12 mm.
MK-4 observation device
Combat experience showed that the device users could recognize terrain up to 1000-1200 meters, which is unsatisfactory for the increasing power of modern tanks and SPGs. Additionally, the MK-4 device did not allow for fire correction.
Taking this into account, USA GBTU KA developed and distributed technical requirements for the design of a commander's periscope and fire correction unit. This device was designed by the State Optical Institute and factory #355 in April-August 1944. The device combines the qualities of a MK-4 device (without the rear prism) and a pair of 6x field binoculars.
The device includes markings for fire correction. 6x magnification allows observation for up to 3 km. A batch of devices was produced, and withstood proving grounds trials. However, field trials revealed that the device required improvement in airtightness. This is currently being resolved by factory #393.
Fire correcting tank periscopes.
At the same time, USA GBTU KA ordered a series of tilted block periscopes for a commander's cupola on the basis of the cupola in the American M4-A2 tank. The tilted block observation device is placed in the walls of the cupola, and provides the commander with a good view.
Requirements for producing a commander's cupola that uses observation devices were given to UZTM and factory #75. As a part of the requirements, in order to improve the conditions of entry and exit, the two-piece hatch was made into one piece.
Additionally, in order to increase the agility of fire and ease fire control tasks, the commander's cupola includes a remote control, with which the gun can be aimed in any direction from the commander's seat. This work finished in June of 1945. All T-34 and IS tanks will be equipped with these remote controls and turning mechanisms.
In conclusion on this issue, between May of 1943 and May of 1945, GBTU KA ensured a commander's cupola for all existing and newly developed tanks, and the design of these cupolas is continuously improved.
Currently, by a technical task from USA GBTU KA, a tank rangefinder is being developed, which will be installed in the commander's cupola."