Tony Williams wrote:The penetration of AP projectiles decreased rapidly as the angle of attack decreased, and this particularly affected the German Hartkernmunition used in the MK 101/103 and BK 3,7 anti-tank guns.
APCR rounds were less likely to shatter at high obliquity in comparison with APCBC rounds. APCR rounds used for MK 101/103 and BK 3,7 were no exception.
At 60 degrees obliquity (from normal on the surface), the usual angle from which antitank planes attacked their targets, BK 3,7 could still penetrate 70-60mm of armor. BK 3,7 had no problems in penetrating the T-34s hull from any direction.
Tony Williams wrote:So to get a favourable angle of attack onto a tank's upper surfaces would have involved a very steep dive from above, which not even the Ju 87G could manage (the weight of the guns prevented recovery from a steep dive).
That's hardly the case. The usual dive angle from which tanks were atacked was a mild 30 degrees.
Tony Williams wrote:OTOH, the rear armour of tanks tended to be less than the side and much less than the front, so the tankbusters could approach from the rear and still get penetration with guns much weaker than the normal ground-based anti-tank guns.
T-34, the usual target, had the same armor thickness all around the hull, 45mm. Two of the most important reasons why attacks from the rear were prefered were: 1) more flammable components were located in the rear (so that they were less exposed to enemy tanks), including ammunition storage, which was located in the rear turret of T-34-85; 2) the more vulnerable upper hull area was larger in the back, because Russian tanks had the turret placed in front (the turret was an obstacle, in general being more difficult to penetrate, although T-34 rear turret armor could be easily defeated by BK 3,7).
Tony Williams wrote:I have posted an article on my website - 'Tankbusters: Airborne Anti-Tank Guns of WW2' - which gives details of the guns, their ammunition, their armour-piercing performance and the planes they were fitted to. Just scroll down the front page until you reach it.
I went there and I saw a mistake. You say about BK 3,7:
It mainly fired Hartkernmunition ammo, capable of penetrating up to 140 mm / 100 m / 90 degrees although this was halved at a striking angle of 60 degrees.
It's the usual confusion between 30 and 60 degrees, from the vertical on the surface or the horizontal.
If the reference is the horizontal then when you can say that it was capable of penetrating 140mm/100m/90degrees, aprox 120mm/100m/60degrees,
and aprox 70mm/100m/30degrees.
I found 120mm/100m/60degrees(from horizontal) penetration for 37mm APCR round in "Aggressors Volume 1: Tank Buster vs. Combat Vehicle", Alex Vanags-Baginskis and Rikyu Watanabe, Airlife, 1993.