"April 4th, 1941
Report on the trials of a PT-4 periscopic tank sight
Trials were conducted according to directive #145211/s of the Main Automotive and Armoured Vehicle Directorate of the Red Army issued on March 22nd, 1941, by commission #6833 composed of:
- Chairman: deputy commander of military unit 6837 Major T.G. Kuznetsov
- Members:
- Deputy chief of artillery supply of unit 6833 Sr. Lieutenant Burkov
- Chief of ammunition supply of unit 6837 Lieutenant Kochegarov
- Also present:
- Aim of the trials:
- Determine the sensibility of adopting the PT-4 sight into service to replace the PT-1 sight.
- Determine the comfort of using the PT-4 sight to fire and observe.
- Determine the sensibility of introducing a new vertical calibration device.
- Supply of trials:
- Two PT-4 sights produced in 1940 were tested: ##110 and 127, installed on BT-A-7 tanks (tank commanders Jr. Sergeant Melnikov and Jr. Sergeant Tokarev).
- In parallel, a PT-1 sight #8064 produced in 1939 was tested in a BT-A-7 tank (tank commander Yefreytor Glushenyuk).
- Firing was performed using:
- 500 7.62 mm rifle cartridges
- 150 45 mm rounds
- Trials programme:
- Inspection and familiarization with the PT-4 sight.
- Installation and calibration of the PT-4 sight in the tank's turret.
- Firing in daytime and nighttime.
- Checking the sight drift after all trials.
- Removal of the sight.
- Trials results:
- Installation and calibration of the PT-4 sight in the tank's turret. Installation of the PT-4 is no different than installation of the PT-1. Compared to the PT-1, the vertical calibration is greatly improved. It is quick and easy to do, and impossible to break (there is no longer a worm gear).
The illumination device can be turned on by none contact (instead of two like on the PT-1). The lighting of various components is satisfactory and allows for comfortable work.
The PT-4 sight #110 has no illmination of the target angle scale. The lack of illumination of the target angle scale does not affect the work of the sight.
The attachment of the forehead rest with a screw on the left sight ensures a stable attachment. The firmness of the forehead rest is no different than that of the PT-1 sight. It is worth remembering that the side ribs of the forehead rest should be made even though the design has not changed. - On firing at daytime and nightime:
During the day exercises ##3, 4, and 7 from ABT instructions KOP-1938 were performed from standstill and exercises ##2, 5 were performed in motion. At night exercises ##3, 4, 5, and 7 were performed from standstill.
Exercise from KOP-38 | PT-4 127 | PT-4 110 | PT-1 6064 | |||
Daytime | Nighttime | Daytime | Nighttime | Daytime | Nighttime | |
3 | Excellent | Good | Good | Excellent | Good | Satisfactory |
4 | Excellent | Excellent | Excellent | Good | Satisfactory | Satisfactory |
5 | - | Good | - | Excellent | Satisfactory | Satisfactory |
7 | Excellent | - | Excellent | - | Good | Satisfactory |
2 | Excellent | - | Excellent | - | Good | - |
5 | Good | - | Excellent | - | Unsatisfactory | - |
Results showed the following advantages of the PT-4 sight:
- It is more comfortable to aim and correct fire as the sight permits adjustment without taking the eyes off the battlefield. The scales are within the field of vision and do not obstruct observation. It is significantly easier to aim when the scales and target can be seen at the same time. A lack of space in the center of the crosshairs does not impact the aiming ability.
- The gun can be fired at night. All scales and crosshairs are illuminated at night. The advantage of the PT-4 is that the eyes do not have to adjust when setting the sight, as it happens with the PT-1.
- On checking the condition and calibration of the sight after trials: all mechanisms of the sight worked normally after trials. No decline of optical qualities was observed. The vertical adjustment did not drift. On the PT-1 sight the vertical adjustment drifted by 0.04 angle markings.
Summary:
- The PT-4 tank periscopic sight is significantly more comfortable compared to the PT-1 due to the presence of the sight scales within the field of vision during the day or night.
- The illumination of the sight scales is reliable and comfortable. One drawback of the system is that the scales and crosshairs are lit too brightly and the light tires the gunner's eyes.
- The PT-4 vertical adjustment mechanism allows the sight to be adjusted reliably and does not drift after lengthy work. One drawback is the small diameter of the heads of the three screws that hold the sight arm in place. The diameter of the heads and grooves need to be cut deeper.
- The study of the PT-4 sight is easy and simpler than the PT-1 sight.
Conclusions:
- The PT-4 sight offers significant advantages in comfort and usage characteristics.
- The PT-4 should be recommended to replace the existing PT-1.
- The aforementioned drawbacks should be remedied.
Commission:
Major Kuznetsov
Sr. Lieutenant Burkov
Lieutenant Kochegarov"