Gun Choices

[Mongoose]

Can someone point me to a source that discusses why each country choose the aircraft guns that they did?  The U.S. used 50 cal almost exclusively, but other countries used 20 mm more often.  Why did the U.S. stick with the 50 cal?  Why did Britain use 30 cal so much?  I would like some insight as to how these decisions came about.

[Chalenge]

Get a book on the Hawker Hurricane development. Nearly all of your questions will be answered.

[FLS]

Here's a couple links.

http://spitfiresite.com/2010/04/cannon-or-machine-gun-the-second-world-war-aircraft-gun-controversy.html

https://www.quora.com/Why-did-American-planes-during-WW2-not-have-a-20mm-cannon

[mikeWe9a]

In the case of the US, development of aircraft armament was minimal during the inter-war years.  As a result, the US really had no well developed, reliable aircraft cannon at the start of WWII - the M2 .50 machine gun was first developed during WWI, and as such was available and reliable, and was the heaviest weaponry commonly deployed on US fighter aircraft prior to WWII (the .30 MG was also pretty common).  The US Army and Navy both desired to transition to cannon armament as soon as possible, however.

The US licensed and built the Hispano 20mm cannon as the M1, but the weapon was unreliable, with misfires due to light strikes from the firing pin being common.  With wing mounted armament, the guns were normally cocked on the ground before flight with no method of cocking or cycling the weapon if a misfire or jam occurred.  The P-38 was able to use the cannon, because the nose mounted position allowed room for equipment to re-cock the gun in the event of a misfire.  Up through the end of the war, the US was unable to produce a 20mm cannon that was reliable enough to deploy as a standard armament in aircraft with wing-mounted guns.  This trend had continued even though the design had been modified into the M2 and later M3 in attempts to increase its reliability.

Mike

[Chalenge]

Isn't it interesting that the U.S. Navy had Oerlikon cannons in large numbers on nearly every ship, but didn't consider it for aircraft use?

[Mongoose]

  Thanks, guys.  That answered a lot of questions for me.  That page from the spitfire site was especially helpful.

[drgondog]

When Material Command was writing Pursuit specs in 1937-1944, heavy armament including 20 and 37mm cannon for all interceptor class Pursuit.  The reason you didn't see them is that only the P-39 and P-38 and P-61 survived the development process. That said not all Pursuit was specified for anything larger than 30 and 50 Cal. The mid and late 30s saw the P-40 and P-43 and then P-47 settle on 50 caliber by 1941-42.

As a side note, the XP-51F/G were in the que as interceptors (Not escort w/o the fuse tank) and the four Oldsmobile 20mm wing battery was in the works for production P-51F as a fast, long range capable interceptor.

Another side note: NAA proposed a series of extremely heavy cannon options for the A-36 including wing 20mm and pod mounted 37mm cannon (combined).

[atlau]

I think part of the reason why the USAAF stuck with the m2 is due to its reliability and that it was perfectly adequate for its primary targets whereas LW fighters needed heavier armament to deal with bombers. 

[save]

German 109E3-E7 had a centermounted 20mm already during BOB, and Brittish did not, although only the slow muzzle velocity 20mm FF.

The .50 cal did it's job, a testimony of that was that all GAF fighters from 1943 replaced the 7.7mm with  13mm machineguns.

The Germans developed the Minengeschoss 20mm/30mm to deal with bombers, with a very high content of explosives in the shell.