Shell scandals in the Red Army in 1940-1941 that went unnoticed
In the early spring of 1941, two defective hulls with turrets were fired upon tank T-34 tanks were fired to determine the effect of armor plate cracks on their resistance to shelling. The shelling was conducted with 37–76,2 mm caliber guns and various projectiles, including experimental ones.
Firing tests revealed that cracks in the hull and turret plates had minimal impact on their resistance to shells. However, the same tests led to an unexpected conclusion unrelated to cracks: they revealed the poor quality of the standard 45mm armor-piercing rounds (APC). This observation is the focus of the following analysis.
Thus, according to the table below, the through-penetration limit (PSL) of a standard blunt-nosed armored vehicle (standard 0130) when hitting at normal speed was more than 760 m/s for armor sheets 45 mm thick, which gives an armor/projectile coefficient (according to the de Marr formula) of 2890 units.
It's important to define the scale right away: the higher the K coefficient, the more the armor resists the projectile—or, equivalently, the worse the projectile's performance. The reference design value for Krupp cemented armor (KTs) in the USSR at that time was 2400 units; anything significantly higher indicates excessive "resistance," which is, in fact, a weaker projectile.
Not armor, but shells
One could justify these results by citing the high armor resistance of the MZ-2 econom armor (a grade of armor made from ship scrap), but data from firing at the same hulls and turrets with other 45mm and 37mm caliber projectiles doesn't allow this. Firing at the 45mm pointed-nosed gun carriage-test projectile (drawing 2-01991) showed only a slight decrease in the armor-to-projectile ratio—known in professional jargon as the "plate price," or armor resistance expressed numerically—to 2660 units when firing at 45mm armor.
The 37mm shells demonstrated mediocre resistance for the MZ-2: K = 2295 for a thickness of 45mm. As a reminder, the armor-to-shell ratio calculated in the USSR at that time for armor penetration tables was 2400 units and corresponded to Krupp cemented armor (KTs).
Thus, in the author's opinion, the issue isn't the superior armor, but the poor quality of the standard 45mm shells. Furthermore, the use of blunt-nosed shells with undercuts didn't help the 45mm gun much: their armor penetration was slightly higher when hitting at normal angles—at K = 2662–2706 (the table below is likely an error: the penetration rates for the vertical 45mm side are reversed).
Moreover, the T-34 hull and turret test report contains no evidence of defects in the standard 45mm shells. Otherwise, one would have to assume that all three types of 45mm shells were defective (according to the report, a total of over three hundred rounds were fired—the exact number requires verification against archival documents), including the two experimental types, which is highly unlikely.
The reason is the shape of the head
According to the author, the most likely reason for the low armor penetration of 45mm blunt-nosed projectiles is the shape of the ogive, or, in other words, their bluntness (see appendix). The principles of improving penetration through the shape of the warhead have been developed since the late 19th century; I leave the specific attribution of priority and dating to clarification from sources. The superiority of blunt-nosed projectiles in penetration over sharp-nosed ones was also demonstrated during armor testing as part of Research Project No. 25 in 1936.
Why, then, in real-world fire, couldn't the standard 45mm shells penetrate either 50mm of homogeneous or 50mm of cemented armor at point-blank range? Apparently, the advantage of blunt-nosed shells depended on the thickness of the armor plates—or, more precisely, on the ratio of armor thickness to caliber: 30mm plates were easily penetrated by blunt-nosed shells (a ratio of 30/45), but as soon as the ratio increased to 40/45 or more, blunt-nosed shells lost out to sharp-nosed shells.
For example, according to a document on actual armor firing, a 30mm cemented plate ("plate price" - 2400) was penetrated by a standard blunt-nosed 45mm BBS from a range of 1000 meters at an angle of 30°. The normalized thickness at this angle, as well as the projectile's energy conservation at this range, mean that at point-blank range, this projectile should have been calculated to penetrate approximately 50mm of KTs armor with 100% probability. However, this did not occur, even against the highly hardened homogeneous armor of the MZ-2.
For reference: the calculated armor penetration of a 2400-kJ KTs plate with a 45mm armor-piercing round at the muzzle was 58 mm at normal range. With 40mm of armor, the K coefficient increased to 2604: at an angle of 30°, the standard 45mm APFSDS could penetrate this armor only from 150 meters.
Why didn't you switch to pointed-nosed projectiles?
Why didn't they switch to sharp-nosed projectiles? The quality of the projectile steel was also a factor: according to the document below, sharp-nosed projectiles provided better armor penetration only if they were made from higher-quality (and more expensive) tool steel using special heat treatment. It was precisely this high cost and complexity of production that hindered their transition.
Thus, the blunt-headed projectile provided two advantages at once: firstly, it was made of relatively cheap steel; Secondly, provided satisfactory penetration of armor, the thickness of which was noticeably less than its caliber.
Customer reaction and consequences
Since the blunt-nosed projectile was considered acceptable within the accepted logic, the unsatisfactory results of firing 45mm APFSDS at two T-34 hulls and turrets—both in the spring of 1941 and in an earlier data series in the fall of 1940 (see the commission's conclusions in the appendix)—in the author's opinion, did not cause any particular concern to the customer. Underestimating the actual armor penetration of the mass-produced 45mm artillery, was likely one of many factors that allowed enemy tanks to reach Moscow, Kyiv, Leningrad, and Stalingrad. It should be noted, however, that the military failures of 1941 were multifactorial and cannot be reduced to the quality of 45mm shells. Nevertheless, 45mm tank and anti-tank artillery was in widespread use, making the weakness of its standard armor-piercing shell all the more noticeable.
And if the measures taken on the basis of the firing test in the spring of 1941 may seem too late (the development of the 57-mm ZIS-2 cannon), then, according to information available to the author, no clear decisions on the part of the Main Artillery Directorate regarding the data on the low armor penetration of the standard 45-mm BBS in mid-autumn 1940 are recorded in the documents, which may be connected, among other things, with the general reorientation of the department to new calibers.
Information about a 1938 batch of defective (overheated) shells from one of the factories did not change the overall picture of the weak effect of blunt-nosed shells on armor with a thickness close to the caliber of the 45-mm BBS.
And finally, the responses of Comrade Beria from two different departments.
application
From the conclusions of the commission on the results of shelling of armor in 1940.
"The commission also noted that the effect of the 37-mm sharp-nosed armor-piercing projectile (drawing no. 3882) when fired at normal angles at plates up to 35 mm thick was weaker than that of 45-mm blunt-nosed armor-piercing projectiles. When firing at plates 35 to 40 mm thick, the effect of both projectiles was approximately equal, and when firing at plates 45 and 50 mm thick, 37-mm sharp-nosed armor-piercing projectiles were superior in their effect on armor than 45-mm blunt-nosed projectiles. When firing at armor plates 25 to 50 mm thick, positioned at an angle of 30° to the vertical, the anti-tank velocity determined by firing 37-mm sharp-nosed armor-piercing projectiles was lower than that determined by firing 45-mm blunt-nosed armor-piercing projectiles. The through-penetration limit for 37mm shells hitting armor plates up to 40mm thick had higher absolute velocity values than the through-penetration limit for 45mm blunt-nosed armor-piercing shells. When hitting armor plates thicker than 40mm, the impact of 37mm sharp-nosed shells was greater than that of 45mm blunt-nosed shells. For example, at an impact velocity of 760 m/s, a 45mm blunt-nosed armor-piercing shell (standard 0130) could reliably penetrate only a 45mm plate, while a 37mm sharp-nosed armor-piercing shell (drawing no. 3882) penetrated a 50mm armor plate made of MZ-2 steel at this velocity.
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