Caliber(s)?

Question

In world war two, why were we (usa/usaf)the only one to use .50 caliber shells and everyone else use 7.7 (.303 cal.) rounds? Why diddent our bombers (b-17, b-24, etc) carry 20mm cannons instead of .50 caliber turrets?

Answer 1

The Germans started off the war with a mic of machine guns and canon on Me109s, the Japanese also had a mix of machine guns and canon. The UK started with .303 but moved to 20mm canon on fighters and sometimes .50s on bombers. The UK also flew B24s, one of my friends got a medal for what he did in one in the far east. The typical armament of late WWII British fighters was 4x20mm, the Mosquito had 4x20 and 4x303 in its fighter variant, there was even an anti shipping variant with a Molins 6 pounder semi automatic anti tank gun. The history channel tends to ignore the fact that UK aircraft were up armed very early in the war, they are also confused over the variants of Mosquito and seldom mention the Typhoons, Tempests and Griffin engined Sptifires.

I think at least one US bomber did have a 20mm canon in the tail.

Another friend flew Corsairs for the US and his squadron was converted to 20mm canon. He said he only saw one Japanese bomber in this whole war, he got up to it and pressed the fire button and it just came appart. I had never heard of 20s being fitted to Corsairs.

Why didn't the UK use six 50s instead of 4 20s? Because the 4 20s were way more effective.

Check out the gun fighter web page, below. I think you'll find that there was a lot more variation than you thought.

Answer 2

an addendum answer: the one reason not touched on is amount of space available in the gun positions of the bombers for the ammunition.

although rather large, a fifty caliber round did take up less space than a 20mm cannon shell. that, and the higher rate of fire from a 50 caliber weapon versus a 20 mm cannon made it more desirable to have as an anti aircraft type system for the larger bombers.

the 50 caliber weapon is impressive. the b-25 gunship was often equipped with 14 forward facing fifty caliber weapons (2 in the upper turret, four in bolt on fast packs on the fuselage, and eight in the nose). these weapons could (and often did) disable Japanese destroyers by simple strafing the bridge and engine rooms.

yes, the B-29 did have a cannon for the tail position. seems when they stripped down this bomber for the over japan bombing raids by removing some of its armament, they left the tail cannon in place as it was the favorite position for an enemy fighter to attack from. and yes, one 20 mm cannon shell could ruin a fighter pilots whole day. so in that case quality vs quantity did matter.

Answer 3

I guess it was the American tendency towards keeping everything highly standardized. It's easy to produce large quantities of only one type of ammunition.
Anyway, as the war progressed, larger calibers were introduced to American warplanes. For example: the P-61 Black Widow had 4 x 20mm Hispano Suiza cannons. The P-38 Lightning had one 20mm cannon, in addition to 4 x 0.5 machine guns. The two Grumman types (that missed the war, addmitably, but were planned and built during it) - F7F Tigercat and F8F Bearcat also had 20mm cannons.
And then, of course, there is the mighty 75mm cannon that the B-25H had.

Answer 4

.303s were quite ineffective (which is why the Spit and Hurricane needed eight).

20mm cannons had a slow rate of fire and were very heavy.

The .50 cal had a high rate of fire and could be armour piercing or incediary. Eight on a P-47 could turn a 109 into burning scrap metal in half a second.

The advent of the GE six-barreled 20mm cannon with a 6000RPM firing rate has allowed one gun to replace several.

Answer 5

Just like the small arms rifles during the war, we had .30/06 (Garand), The Brits had .303, the Soviets had 7.62x54r, the Germans had 8mm, every country seemed to have their own personal favorite.
Even in Vietnam, our rifle was 5.56, the VC had 7.62x39.
Since that time, most NATO nations have gone to the same caliber (Hence, the US retiring the Colt .45 Auto, replacing it with the 9mm Beretta)