"Conclusions on the T-70 tank's armour, developed at the Gorkiy Molotov Automotive Factory
The T-70 has the following main armour components:
- Upper front plate: 35 mm at 60 degrees
- Lower front plate: 45 mm at 30 degrees
- Sides: 15 mm at 0 degrees
- Rear: 25 mm at 45 degrees
- Front floor: 15 mm at 75 degrees
- Upper rear plate: 15 mm at 75 degrees
- Turret (cast): 45 mm at 30-45 degrees
- Gun mantlet (cast): 50 mm at 0 degrees
- Turret and hull roof: 10 mm at 90 degrees
- Floor: 6 mm at 90 degrees
The analysis of the robustness of components was done after firing with the 37 mm gun using blueprint #0129 shells at muzzle velocity of 820 m/s. The results are shown in diagrams 1 and 2. Diagram 1 graphically shows distances of the limit of penetration (PTP) for various components of the hull and turret when shooting into the front, rear, and side of the tank. From this diagram, it can be seen that various components are not equal in shell-resistance.
For instance, when shooting at the front, the gun mantlet and LFP are more or less equally robust (PTP distance is 250-300 meters), but the UFP does not suffer damage at even 50 meters. Calculations show that a 25 mm UFP will be equally robust compared to the LFP.
As for the effective thickness of the front armour, it is sufficient, and gives satisfactory resistance to shells.
The rear armour becomes impenetrable at only 630 meters. In order to make it as resistant as the front, it must be 35 mm thick.
The sides can be penetrated at 2000 meters. However, this does not show the whole picture. For instance, the data in diagram 2 shows that the tank can only angle itself by +/- 15 degrees, as at a higher angle, its sides are vulnerable. This kind of limit to maneuverability is unacceptable, and the sides must be increased to 25 mm at least. 25 mm armour will give the ability to angle up to 30-35 degrees, which is satisfactory. 30 mm will further increase that to 40 degrees.
The turret armour resists shells completely from 160-325 meters. As only a small portion of the turret can be penetrated at 325 meters, consider the turret armour satisfactory.
From the analysis of the hull and turret, it can be concluded that:
- The sides must be at least 25 mm thick.
- If the vehicle is overloaded, the thickness of the UFP can be reduced to 30 mm, but this is highly undesirable.
- It is necessary to remove the discrepancy in robustness of the turret at various angles of tilt, which can easily be done with a cast turret with a thicker lower part.
- The robustness of the driver's hatch hinge is insufficient due to a small surface area that is welded. If a shell hits it, it can fall off.
- The protection of the turret observation device from bullets is insufficient, as bullets will deflect from the armour and strike the observation device with lead drops and fragments.
- It is desirable to change the coolant grille, as its current design is vulnerable to grenades and incendiary fluid.
Diagram of penetration (PTP) of the hull and turret of the T-70 tank when fired upon by a 37 mm gun using sharp-tipped armour piercing shells made according to blueprint #0129
Distances are in meters.
Chief of the Technical Department of the 3rd Directorate of the People's Commissar of Tank Production, Smolenskiy
Senior assistant to the Chief of the 1st BTU Department of Red Army GABTU, Military Engineer 1st grade, Burtsev
February 25th, 1942."
CAMD RF 38-11355-950