What lessons from WW II show that the 9MM was a bad sub machine round. Curious, The 9mm makes an excellent sub-machine gun round. By the way,compared to the Swedish K the M-3 sucks. The Thompson, 11 pounds of steel unloaded, OK,. you lug around that much weight in the boonies and see how long you last. The only one carrying Thompson's ( and M-3s) were the cooks in the rear area. Guys, I know you weren't there but read up a little bit more before you make these statements. Do you even know why the Thompson and M-3 are in 45 caliber?? It has absolutely nothing to do with combat effectiveness. It has to do with the same reason the Garand is chambered in 30-06.
Submachineguns, as shown in WWII, are specialty weapons for a combined weapons team. They are limited in range, and tend to be less accurate than rifles at anything beyond 75 yards. In a jungle, they tend to be lots of sound and fury, but distances allow a skilled user to be more effective. The cartridge, however, is still that of a pistol, and there's a lot of cover against an SMG in triple canopy.
The Marines of WWII made good use of the Thompson in the Pacific. The M1A weighs 10.8 pounds, by the way. At least that's what the WWII manual says.
With the limited use of an SMG, one caliber is much the same as another. The Russians armed entire battalions with the SMG firing the 7.62x25 round, and had them operate in close proximity to tank formations.
I was there, were you? Please, it doesn't sound like it. The M14, standard issue until 11/67, also weighs in at almost 10 pounds. I never understood the "weighs so much" crap. The M1 Garand of WWII and Korea was in excess of 10 pounds, and those poor soldiers walked one
heck of a lot more than the soldiers of Vietnam.
If you actually set foot in Vietnam, and saw cooks with Thompsons, it seems like you must have been working with them. We called them REMFs, and they were
ALL SEALS, Rangers, Green Berets, Pathfinders, and SOG. You can read about their exploits all over the Errornet.
The .45 ACP was the standard caliber for all American forces from 1911 until 1986. Perhaps that's why the SMGs were .45 ACP.
The Garand was initially designed to be capable of firing a smaller, less capable, round. However, with literally millions of 7.62x63 rounds in inventory, and all other rifles chambered for it, a wise decision was made to standardize at that caliber.
What's with the revisionist bent? The two U.S. calibers were both the result of wartime experiences, and, for the day, scientific research. That was why they were standardized. That the Germans chose the 7.92x57, and the 9x19 is hardly a reference, as they tended to lose. WWII being the second time in less than 30 years. The British pistol caliber was the .38/200, an abysmal choice.