B-17 Fortresses and B-24 Liberators under attack

The MK 108 Maschinenkanone 30 mm caliber autocannon manufactured by Rheinmetall-Borsig. A requirement for a heavy aircraft weapon for use against the Allied heavy bombers. Requiring on average just four hits with high-explosive ammunition to bring down a B-17 heavy bomber and a single hit to down a fighter. There were two main types of ammunition for the MK 108 to use, a 30 mm high-explosive self-destroying tracer ("M-Shell" or "Mine-Shell") and a 30 mm incendiary shell. The first type was designed to cause a maximum blast effect by combining a very thin shell casing with the maximum load of explosive. Tests carried out at Rechlin (where most of the Luftwaffe aircraft and weapons tests were done) showed that with a "M-Shell" with 85 grains of explosive, five hits could destroy a B-17 or B-24 bomber. The second type of shell, the incendiary, was meant to be targeted at the fuel tanks of the enemy plane. Since some penetrating force was still needed to overcome the armor or airframe of the target, and not have the shell break up or explode upon contact, a hydrodynamic fuse was fitted so that the shell only exploded once it came into contact with liquid.