The R4M was developed in order to deal with the increasing weight of anti-bomber weapons being deployed by Luftwaffe fighters. The primary anti-bomber weapon of the Luftwaffe for much of the war was the 20 mm MG 151/20 autocannon, which was compact enough to be mounted in an internal wing bay mounting in the Focke-Wulf Fw 190 (up to 4 cannon, or 6 with optional twin-gun underwing pods) and also fitted on the centerline of Bf 109G fighters, firing through the propeller spinner as a Motorkanone. This could be supplemented by an additional pair of cannon in drag-inducing underwing gun pods, but it was found that it took an average of twenty 20 mm hits to shoot down a typical four-engined Allied bomber.