Why did the US ww2 fighters have 50 cals instead of 20mms like their european cousins

[PAT303]

I'll tell you a story, I had a patient named Arthur who was an Oerlikon gunner who fought at Milne Bay, he told me the story behind his injuries. In one of the battles the captain of the small supply ship he was on pulled right up to the beach so Arthur and the other gunners could give direct fire support to the diggers retreating through the jungle, Arthur stated that he could see the diggers running back, firing and running back with the Japanese right on them, he started firing horizontally across the beach sweeping the jungle behind the last digger he could see, next thing he took two bullets into his right calf but he jumped back up and continued fighting, he had a second bloke changing the drums, the barrel was smoking but he kept at it until there was a great explosion that knocked him out, he later woke up in hospital the next day, apparently the barrel was so hot the gun malfunctioned and the shell being chambered detonated setting off the ammunition that chained reacted in the drum which exploded knocking him out, I last saw him when he was 90 and used to picked shrapnel out of his body that still worked it's way to the surface after all those years, he was 17 when this happened.

 

[Barrett]

Sidebar:
There was no "F-4U" because that would have been the ultimate version of the McDonnell-Douglas Phantom II.

The subject has arisen elsewhere online, which seems peculiar because the US deployed cannon-armed aircraft including
P-38s
P-61s
F6F-5Ns (some with mixed .50 cal/20mm armament)

 

[Shortround6]

And some P-70s and A-20Gs. But here again the US seemed to be a day late and dollar short. The A-20s got guns with 60 round drums and what ever the firepower advantage they had for 6-7 seconds all the later P-20s and A-20s got 6-8 .50 cal guns with sizable belts for longer firing time.

 

[GTX]

Will eight .50 cals fit in the nose of a whirlwind?, I think you will struggle getting more than four with ammunition.

Well there was a proposed 12 x 0.303 version:

 

[PAT303]

The .50 is a much bigger gun than the .303, my guess like the Hispano only four would fit.

 

[Shortround6]

The .50 is a much bigger gun than the .303, my guess like the Hispano only four would fit.

I would guess at least six.
There was a mock-up nose for the Whirlwind with four 20mm guns with the air powered magazines with 115-120rpg gun and three .303s across the top.
There was more room inside the nose once you got rid of the drums.

 

[Jabberwocky]

US-manufactured 20mm cannons being badly unreliable had a lot to do with that.

I'd argue it was even the primary reason.

Tony Williams has a excellent write up on some of what when wrong with the US 20mm programme.

Modifications and Attempts at Standardization

Chinn in The Machine Gun also devotes a considerable amount of space to the problems (see page 577-582 and 588-590)

HyperWar: The Machine Gun (Vol. I/Part V)

What's staggering is that the US ended up producing nearly 135,000 20mm cannon but only supplied 34,500 to the AAF and Navy. Another 44,000 were provided as 'international aid'. And 55,000 ended up in storage, never to see the light of day.

I think one of the other reason for the failure to adopt the 20mm was that there was always the idea that something better was just on the horizon.

In the years leading up to WW2 and during the conflict, the US did an immense amount of mucking about with designs for very heavy machine guns and light/medium cannon. Apart from the Hispano and various derivative designs, there were multiple other light cannon designs in 15mm/0.60 caliber, 20mm, 23mm and 25mm. And a bunch of .90 calibre projects. And the 37mm that ended up in the P-39/P-63 and very early production P-38s.

During WW2, the US was looking for something with a REALLY high velocity to stick on their aircraft. Someone had worked out that for deflection shooting that if you cut the flight time by 1/3rd then the chance of a hit went up by 400% for the average pilot. So, they proceeded to do all sorts of experimental things, mostly based around a .60 caliber round moving at somewhere north of 3500 feet per minute.

 

[PAT303]

Were do the ammunition belts go with six .50's?

 

[ThomasP]

I would expect somthing similar to the arrangement in the P-38. Whether the magazines were under the guns as in the P-38 or above the guns as in the Whirlwind I do not think would matter. Note the 20mm in the image below is fitted with the 60-round drum, which gives an idea of scale & space available. The P-38 is a larger aircraft than the Whirlwind - so maybe not as many rounds per gun?

 

[Shortround6]

Were do the ammunition belts go with six .50's?

Were do you want to put them?
Post #66 top picture, upper left side, Four 20mm guns (like the lower photo) with 115-120rpg, take them out and put in four .50s with well over 200rpg.
Take out the three .303s with 1200 rounds between them and stick in two .50s with several hundred rounds each.

Take the nose with the twelve .303s and put two .50s in each row instead of four .303s.
take out the 6,000 rounds of .30s and in 200 rpg, 1200 round total. adjust upward as needed.

.50s and their ammo were big, they were not 20mm guns/ammo.

 

[PAT303]

Were do you want to put them?
Post #66 top picture, upper left side, Four 20mm guns (like the lower photo) with 115-120rpg, take them out and put in four .50s with well over 200rpg.
Take out the three .303s with 1200 rounds between them and stick in two .50s with several hundred rounds each.

Take the nose with the twelve .303s and put two .50s in each row instead of four .303s.
take out the 6,000 rounds of .30s and in 200 rpg, 1200 round total. adjust upward as needed.

.50s and their ammo were big, they were not 20mm guns/ammo.

Sounds plausible, I'd go all three if possible in the BoB, it would have made a fantastic He111 killer

 

[yulzari]

Sounds plausible, I'd go all three if possible in the BoB, it would have made a fantastic He111 killer

Surely 4x20mm cannon as IOTL would be better. They had the cannon and the ammunition already. What they needed was more aeroplanes bolted to the back of the cannons. Hence the back up 12x.303" which used existing guns and ammunition.

 

[PAT303]

First choice would be cannons for sure, the HEI rounds were reliable and the solid steal practice rounds were found to penetrate as good as dedicated AP rounds so that would choice number one, saying that I wouldn't want to be in a bomber that was hosed lengthways by 12 .303's.

 

[BarnOwlLover]

In a thread where I asked about all 6 .50s in the P-51D/H having 400 rpg, it was def. suggested for a time that had the XP-51F entered production as an interceptor, it would've had 4 20mm cannons, and it seems that there was a XP-51F mock up with the cannons fitted, instead of the P-51H (NA-117) mock up.