RAF Heavy Bombers & Defensive Capability

I was watching the BBC 2 TV programme on the 70th anniversity of the Dambuster raids from RAF Scampton. I once went to Scampton many years ago when at school and in the school ATC.

I have often wondered why RAF WW2 Heavy Bombers such as the Lancaster were never equipped with the US .50 cal. heavy machine gun for defence. Was the .303 machine guns that were used right through the war more effective than .50 cal. machine gun such as the USAAF used on their B17, B26, B29 heavy and medium bombers?

What was the effective differences between a .303 machine gun, and a .50 cal. one as far as aircraft defence is concerned.

In the early days of WW2 when the RAF were unwise enough to try out bombing in daylight, it's recorded that the twin .303 Brownings in the tail turret of early Wellingtons, were a nasty shock for Luftwaffe fighters. Presumably the more usual 4-gun turrets were even more effective, but not sufficiently so to prevent a high rate of losses on daylight raids. Wisely there was a switch to night bombing. Before dedicated night fighters appeared, flak was the main defence employed by Germans, the bombers' small calibre MGs would hardly be used. Later, when ground radar was supplemented by Me 110s & Ju 88s with airborne detection systems, defensive armament was more necessary and .303s were effective enough at the closer ranges employed at night.

The US Army Airforce stuck with large formations on daylight raids, hoping that the longer ranging and harder punching .50 cal guns would give adequate protection from attacking fighters which came in more quickly and in greater numbers than would have been possible at night. Unless the B17s & B24s had fighter protection, even up to 13 x .50 cals on each aircraft couldn't prevent heavy losses.

As the war went on, although both US & Axis bomber aircraft were up gunned with heavier MGs or cannon. the RAF stuck with the .303 for night operations with heavy bombers and even for Coastal Command activity over the Atlantic. Operational squadrons did plea for the heavier guns and, later on, the Rose turret with twin .50 cal MG replaced the 4 x .303 installation on some Lancasters. On occasion, and after D-Day. the heavies were used on one- off daylight raids but by this time the Allies had air superiority and the danger from enemy fighters was minimal.