Soviet Armour Research

When you're fighting a war, it's not only important to know how well your guns work against enemy armour, but also important to know how well the enemy's guns work against yours. As always, NII-48 has us covered, with its report titled "The study of the penetrative function of German captured tank shells on domestic tank armour, and methods of combating them", stored under CAMD RF 38-11355-776.

The report first goes over the various German guns used, and the ammunition types: AP sharp-tipped, AP sharp-tipped capped, APCR, HEAT, and solid AP, without any explosive filler, damaging the enemy tank with only its penetrative force. There is an exhaustive list of guns and ammunition for them, and it, perhaps, will be the topic of another article.

In order to evaluate the effectiveness of captured ammunition: high hardness plates 25 mm, 45 mm, and 60 mm thick were produced, as well as medium hardness plates 30 mm, 50 mm, and 75 mm thick. The precise chemical composition of the armour is present in the report, and will also likely be included in a subsequent article.

"The tests determined the following:

• APCR shells have a harder time penetrating highly hardened armour than medium hardened armour. Highly hardened armour can be penetrated at a range of angles 10-15 degrees less than medium hardened armour of the same thickness. The 60 mm highly hardened plate resists APCR shells 5-10 degrees better than the 75 mm medium hardened plate.
• Medium hardness armour resists AP shells better, whether capped or uncapped."

The test data is included in the following table, translated for your convenience. PtP stands for Possible to Penetrate. LtP stands for Likely to Penetrate.

"The damage to the armour plates is described as follows:

• APCR forms a shallow dent from the casing, and a deeper dent or penetration from the core. When impacting armour of medium hardness, the core does not change direction, and passes through the plate at the same angle it was shot at. In case of armour that is highly hardened, its path changes, as if to ricochet. Upon striking the armour at a large angle, the brittle core shatters.
• The following damage is caused by AP shells with an explosive filler:
• Clean penetration equal to a caliber: the shell penetrated and exploded past the armour. The shell normalized during passage through the armour.
• Penetration with ragged edges, frequently larger than a caliber: the shell detonated or was destroyed during its interaction with armour. This most frequently happens with larger calibers.
• Dent from a ricocheted shell."

The study found that, against hard armour, 50 mm and 37 mm APCR shells do not work as well as AP shells of the same caliber. Also, to no one's surprise, 37 mm guns do not penetrate as much as 50 mm guns.

Tests of a T-34 hull led to the following conclusions:

• The upper front plate of the hull cannot be penetrated by 50 mm and 37 mm shells, barring cases where the tank is tilted forward due to terrain.
• The overtrack hull can be penetrated by 50 mm shells, but not 37 mm shells.
• The side can be penetrated by both 37 mm and 50 mm shells.
• The rear can be penetrated by 50 mm shells. 

Tactical diagram of a T-34. The tank is facing to the left. The top part is with 50 mm APCR, the bottom part is 37 mm APCR. Distances are extrapolated, and given for "possible penetration" (20%).

Tests of a KV hull led to the following conclusions:

• The front can only be penetrated by 50 mm APCR shells.
• The sides can be penetrated by 37 mm and 50 mm APCR, as well as 50 mm AP (in practice, no 37 mm APCR penetrations were found).

Tactical diagam of a KV. The tank is facing to the left. The top part is 50 mm APCR. The bottom part is 37 mm APCR. Distances are extrapolated, and given for "possible penetration" (20%).

Tests of a T-70 hull led to the conclusion that it is only protected from 37 mm shells from the front, which can only be penetrated by 37 mm APCR.

Tactical diagram of a T-70, against a 37 mm gun. Distances are extrapolated, and given for "possible penetration" (20%). 

The report also discusses methods of reinforcing armour, including research into heterogeneous armour and armour screens. Armour screens are described as being effective against HEAT and APCR ammunition, distancing the armour from the shell impact in the first case, and stripping the fragile core of its protection in the second case. 

Factory #9 conducted tests of such screens. The list of the full combination of screens and plate thicknesses is long and tedious but here are their conclusions:

• Screens very close to the armour are not as effective as screens further away.
• A thin plate in front of a thicker plate is superior to a thick plate in front of a thinner plate.
• High hardness screens are superior to medium hardness screens.
• 15 mm armour screens offer satisfactory protection from APCR and AP shells and any distance and angle.
• Against capped AP shells, a 15 mm screen is only effective at distances greater than 150 meters. At distances less than 150 meters, a 20 mm screen is needed. At distances less than 50 meters, a 15 mm screen with a 4 mm secondary screen is needed.
• Against German 75 mm HEAT shells, a 6-8 mm armour screen is sufficient protection.

T-34 with armour screens. Model.

T-34-85 with armour screens. Model.

The results are quite effective, but due to the low amount of APCR and HEAT shells encountered in the field, efforts to screen T-34s were short-lived. Losses due to HEAT were very small: none at all in most of 1942, less than 2% over the winter between 1942 and 1943, and less than 7% in 1943. In 1944, no tanks were lost to HEAT shells from other tanks. Panzerfausts and Panzerschrecks were responsible for 5% of all tank losses that year. Against such portable HEAT weapons, mesh screens were developed. These screens are frequently seen in footage of Soviet tanks in Berlin. However, these screens were not installed on a very large amount of tanks even then, as German infantry tended to be swept out by machine gun fire from the tank and accompanying Soviet infantry at a range of 150-200 meters, greater than the range of the German AT weapons.

T-34-85 tank with HEAT screens. These screens were installed to protect from infantry weapons, not tank HEAT shells, indicated by the screen covering the top of the turret.

The above photograph shows yet another protective measure. One suggestion made by factory #112 was the hanging of five spare tracks in the front of the hull (four are missing in the photo) and two on the back of the turret. 

Based on the experience in the Winter War, the Red Army decided that the potential enemy may develop large caliber guns capable of penetrating Soviet tanks. An order was given in the spring of 1941 to increase the front armour of already built and future T-34s to 60 mm. Two tanks with additional armour were developed in July of 1941. These modifications were discontinued due to the enemy, now no longer potential, lacking any such guns.

In December of 1941, based on news of the Pz III Ausf J and its newfound capability to penetrate the front of a T-34 with APCR, it was decided that T-34s should once again be produced with 60 mm of front armour. Due to the low amount of APCR used by the Germans, this modification was discontinued. Three factories produced a number of these up-armoured T-34s in the winter and spring of 1942.

T-34 with 15 mm of additional armour welded on top of its 45 mm upper front plate, produced by factory #112.

STZ built about 200 tanks with improved armour. Factory #112 built 80 hulls and 109 turrets with additional armour. Factory #112 also cast 8 turrets with the sides thickened to 75 mm. Factory #183 also produced a number of these tanks, but I don't have any data on how many.