The US military decided to bet the farm on their trusty .50 caliber machine guns.
Meanwhile, the other players at the table – the Germans, the Brits, even tthe Japanese forces – were throwing down 20mm cannons like they were pocket change.
So, what gives?
See, the US military brass had a love affair with their .50 cals. They were reliable, easy to produce, and plentiful.
Plus, they could chew through the flimsy aluminum of Japanese planes like a fat kid through a box of donuts.
So, on paper, there wasn't much incentive to switch to a heavier, more complex weapon.
That's not the whole story though.
The 20mm Hispano-Suiza cannon, favored by the Brits and adopted by the Americans for some of their planes, packed a bigger punch.
It could shred enemy aircraft with explosive rounds, something the .50 cal could only dream of.
However, the Hispano had some issues.
For starters, the it was a finicky beast. It jammed more often than a cheap zipper, and its ammo was less readily available than a cold beer on a hot day.as
Also, those cannons were hefty, and every extra ounce meant less maneuverability for American fighters. Given the nimble nature of Japanese Zeros, that was a serious consideration.
But perhaps the biggest reason for the US military's reluctance was their unwavering faith in their pilots.
These weren't just flyboys; they were marksmen, trained to squeeze every ounce of effectiveness out of their .50 cals. And to their credit, they did a damn fine job.
Of course, hindsight is 20/20. Looking back, it's easy to say the US should have embraced the 20mm sooner.
Bu t in the heat of battle, decisions are made with imperfect information and under immense pressure.
AN/M2
And while the .50 cal might not have been the sexiest weapon in the sky, it got the job done.
Sometimes, that's all that matters.
Source: Quora
