Originally Posted by
Heathrow Harry
Leafing through some old William Green books I noticed that throughout the total production run of the main US WW2 fighters - P-47,Thunderbolt, P-51 Mustang, Wildcat, Hellcat all were only armed with machine guns . The Lightning carried machine guns and one cannon.
Only the later versions of the Corsair carried 4 cannon.
When you consider than in Europe cannon started to be fitted from 1939 across the fighter types of all nations this seems strange. Especially as the US was relatively quick to adopt self-sealing tanks, cockpit armour etc etc
Any idea why?
As others have noted, they decided (don't have the source material to hand) that for simplicity the standard armament for a fighter was 6x 0.5 inch guns. Don't forget the P-40 - more numerous than any of the naval fighters! This policy was varied slightly to suit specific airframes: the unusual layout of the P-38 and P-39 allowed space for a cannon as well as the machine guns, and the size of the P-47 allowed it to have two extra. Conversely, most of the F4Fs had to make do with 4.
The reasoning (IIRC) was exactly as Sloppy Link and Geeram have stated, and I suspect that the Americans felt vindicated when they saw the difficulties which other nations had at times with cannon-equipped fighters (the early Hispano-equipped Spitfires but also the German MK108). And even a typical mid-war Spitfire was pretty impotent against everything apart from a Zero once the 20mm ammunition had run out and all it had was 4x .303 guns.