Weapons on Fighters of WW2 (AutoCannon)

[Arrawin]

I was wondering what opinions you might have as to why it was that America seemed to prefer a load of machine guns over the use of a few machine guns and a real heavy hitter like the autocannon (one or two)? I may be wrong and I know some of our fighters did have at least 1 autocannon but a lot of them only had like 4 to 8 50cal mg's. Seems like the American aviation community had a little different mindset from the europeans as far as fighter arms were concerned.

 

[swampyankee]

I was wondering what opinions you might have as to why it was that America seemed to prefer a load of machine guns over the use of a few machine guns and a real heavy hitter like the autocannon (one or two)? I may be wrong and I know some of our fighters did have at least 1 autocannon but a lot of them only had like 4 to 8 50cal mg's. Seems like the American aviation community had a little different mindset from the europeans as far as fighter arms were concerned.

My opinion? The USN was dissatisfied with the 0.5 inch pretty early, because its fighters always had a secondary role in attack, and the machine gun wasn't damaging enough against small craft; the USN tried 20 mm in fighters and estimated one 20 mm Hispano was thrice as effective as a 0.5 in M2. The problem was the US couldn't get its act together to produce an autocannon enough better than the 0.5 in, mostly because the 20 mm production was so botched that the gun was far too unreliable for service use until quite late. In the air, the USN/USMC and the USAAF found the M2 was adequate. Post-war, "adequate" became "optimal," and it wasn't until the USAF ran into the MiG-15 that they changed their opinion.

 

[Shortround6]

We have a lot of threads that mention this. The US may have had a different mindset, but they were also trying out a bunch of different things in experiments/development programs.

The US air force did NOT think the M2 was adequate let alone optimal or they would not have funded multiple programs that lead to the M3 .50 cal machine gun.
This gun was used to a very limited extent in WW II, 6-8,000 produced but how many got overseas I don't know. However it was the standard gun in the jets that fought in Korea.
While pretty much identical in appearance to the M2 the M3 fired at 1200rpm (about 50% faster) so six guns in a jet were equal to about nine guns in an old piston plane.
The US air force was also NOT using WW II ammo in the guns. They were using the M23 incendiary round which carried a much higher amount of incendiary material than WW II incendiary ammunition and due to the bullets being lighter they had significantly higher velocity which reduced the amount of lead needed on deflection targets. Please not that this round was service trialed during WW II with not great results but the Air force persevered with not only several redesings but changing manufacturer twice in the search for better reliability/safety. Not quite what one would expect from a an air force that throught the WW II guns/ammo were "optimal".
During WW II the US ordnance dept also developed and number of guns and cartridges of larger caliber. This included 23mm guns (.90 cal) and .60 cal guns (15mm) in addition to high velocity .50cal guns. One of these programs involved necking the 20mm Hispano case down to .50cal. They got a lot velocity but you also need a gun the size and weight of 20mm Hispano to fire it. Very short time of flight to target but barrel life was poor.
The 20mm cartridge used in the Vulcan gun and the M-39 revolver cannon (used in the F-100 and others) is one of the .60 caliber rounds necked up to 20mm.
Think slightly over grown Russian 14.5mm anti-tank rifle round.

The US air force had an obsession with high velocity/short time of flight in order to reduce the problems with defection shooting.

 

[wuzak]

I was wondering what opinions you might have as to why it was that America seemed to prefer a load of machine guns over the use of a few machine guns and a real heavy hitter like the autocannon (one or two)? I may be wrong and I know some of our fighters did have at least 1 autocannon but a lot of them only had like 4 to 8 50cal mg's. Seems like the American aviation community had a little different mindset from the europeans as far as fighter arms were concerned.

It depends on which autocannon.

The M4 37mm cannon in the P-39 was not such a great air-to-air weapon.

The HS.404/Hispano Mk II/V was a pretty good air-to-air weapon.

 

[michael rauls]

We have a lot of threads that mention this. The US may have had a different mindset, but they were also trying out a bunch of different things in experiments/development programs.

The US air force did NOT think the M2 was adequate let alone optimal or they would not have funded multiple programs that lead to the M3 .50 cal machine gun.
This gun was used to a very limited extent in WW II, 6-8,000 produced but how many got overseas I don't know. However it was the standard gun in the jets that fought in Korea.
While pretty much identical in appearance to the M2 the M3 fired at 1200rpm (about 50% faster) so six guns in a jet were equal to about nine guns in an old piston plane.
The US air force was also NOT using WW II ammo in the guns. They were using the M23 incendiary round which carried a much higher amount of incendiary material than WW II incendiary ammunition and due to the bullets being lighter they had significantly higher velocity which reduced the amount of lead needed on deflection targets. Please not that this round was service trialed during WW II with not great results but the Air force persevered with not only several redesings but changing manufacturer twice in the search for better reliability/safety. Not quite what one would expect from a an air force that throught the WW II guns/ammo were "optimal".
During WW II the US ordnance dept also developed and number of guns and cartridges of larger caliber. This included 23mm guns (.90 cal) and .60 cal guns (15mm) in addition to high velocity .50cal guns. One of these programs involved necking the 20mm Hispano case down to .50cal. They got a lot velocity but you also need a gun the size and weight of 20mm Hispano to fire it. Very short time of flight to target but barrel life was poor.
The 20mm cartridge used in the Vulcan gun and the M-39 revolver cannon (used in the F-100 and others) is one of the .60 caliber rounds necked up to 20mm.
Think slightly over grown Russian 14.5mm anti-tank rifle round.

The US air force had an obsession with high velocity/short time of flight in order to reduce the problems with defection shooting.

Alot of interesting information there. I once read that the p47Ns got the faster firring M3s in effect making there eight 50s like 12 of the M2s. Just read this once and never saw anything more about it before or since. Do you happen to know if this is true ?

 

[Barrett]

FWIW:

Maybe 30 years ago I crunched the numbers from Dr. Frank Olynyk's voluminous series containing all US (and some RAF) aerial victories in WW II--continuing into the jet age. I found almost without exception that beginning with a four-gun .50 cal. battery, increasing to six with a 50% increase in firepower only yielded a 10% increase in lethality, based on credits for destroyed-probables-damaged.

In other words:
Four .50s in the F4F-3/FM-2, P-51B/C, etc represented the optimum US WW II fighter armament. You had to get into P-47s before multi-multi 50s showed a significant difference. And as Jimmy Thach said, "A pilot who will miss with four guns will miss with eight."