At the time there was interest in using large calibre guns to attack bombers from outside the effective range of their defensive guns. A number of Me 410s were fitted with a 50 mm gun, but the effectiveness was hampered by the general difficulty in aiming, the limited ammunition supply, and a tendency to jam. Moreover, the considerable weight became a serious liability with escort fighters becoming ever more numerous. For the anti-bomber role, the R4M rocket turned out to be a much better bet, but came too late to have much effect.
Elsewhere, the Soviets made fairly extensive use of 37 mm guns for air-to-air combat and a 37 mm gun had been fitted to the P-39.