Saturday 1 March 2014

Soviet Fire Control

CAMD RF 38-11369-1 (summary of GBTU progress between 1943 and 1945) continues yielding interesting results. The section on commander's sights reveals some interesting inventions. The first part has some old boring stuff that we all know by now (a commander that has to do other things is not going to be able to direct his full attention to commanding, good visibility is important, etc), but then it gets to the good stuff.

"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:
  1. Mirror periscopes were destroyed by nonpenetrating shots.
  2. 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."


  1. "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. "

    This is not clear. Is the armor on the IS cupola 90mm and the armor on the T-34 12mm. Or is the armor on the IS cupola 90mm and the glass 12mm?

    1. The thickness of the glass is 12 mm on the T-34 and 90 mm on the IS. I don't know how thick the armour is on the two cupolas, but I assume the difference is comparable.

  2. The Stenciled thickness on captured IS cupola from top to base is 40mm, 95mm, 85mm. The diagram of design armor for T-34 cupola is 90mm. I wonder why so great a difference in glass thickness.

    1. I would assume that they anticipated that the IS would be subjected to much fiercer beatings than a modest T-34 :)