"John Browning essentially completed all the groundwork on his 37mm automatic gun by 1925..."
The one the P-39 and -63 got? That was intended as an AT gun in the 20s or an example of the long time Ordnance took?
I'm looking forward to your book.
It's complicated. The original gun was offered by Browning in December 1920 to meet a requirement for a 37mm automatic aircraft gun. It was basically an upscaled version of the ..50 BMG firing the Hotchkiss 37 x 97 round. at c. 1400 FPS. Ordnance said great, but can you boast it to 0200 FPS,,,and oh, yeah, how about an AA gun version firing at 2000 to 3000 FPS too? So he built two more guns, the latter of which fired a 37 X 123B round that achieved 2000 FPS. That gun was then rebuilt in 1926 to fire an even more powerful 37 X 224R round that achieved 3000 FPS...and then Browning died.
The upshot was both guns were tested in 1927 and it was found that the high Mv caused excessive wear at the muzzle and it also suffered frequent stoppages...and with Browning dead everyone basically stood around with thumbs up bums while they argued about the carriage design and tried to figure out a way to reduce wear. The Air Corps backed out of the program, but Colt and Ordnance redesigned to cartridge to 37 x 223R with a slightly lower Mv.and the gun - with a water jacket added apparently because it would look cool, but without a carriage - was standardized as the Antiaircraft Gun M1927 and then immediately changed to M1, because, well it was Ordnance and they decided to redesignate everything standardized in 1927 and beyond under a new system. Yay!
They completed three guns. They were then used to test and almost infinite number of carriage ideas. Over the next twelve years. Oh, they also dropped the water jacket, apparently because it no longer was cool. The real problem was the gun was inaccurate, suffered frequent stoppages from failure to eject, continued to suffer excessive wear, so they dropped the Mv to 2600 FPS and redesigned the rifling and eventually had a working gun, the M1A2. Yay!
Meanwhile, the Air Corps also decided to revive the 37mm aircraft gun and went back to the original Browning 1400 FPS design in 1935...15 years after Browning delivered the original pilot. That got tweaked and became the 37mm Aircraft Cannon M4. In December 1939. They then came full circle again, and decided to adapt the 37mm Antiaircraft Gun M2A1 as an aircraft cannon, which eventually became the M9 a few years later.
And all during this time they periodically jury-rigged one of the pilot guns into one of the Ordnance tank experiments, without much success, which is what led the Army to buy the two Rheinmettal 3.7cm TAK in 1935. So no, neither the Aircraft Cannon M4 or the AA Gun M2A1 was ever intended as a tank gun.
BTW, Ordnance never did manage to correct the ejection stoppage problem in the 37mm Antiaircraft Gun M2A1, which was the reason the Army eventually decided to go with the 40mm Bofors.
Edited by Rich, 03 June 2020 - 0032 AM.