Originally Posted by
MandoWookie
9mm Luger is just .30 Luger necked up as an easy way to offer a larger caliber for customers. So no capacity advantage over 9mm, just a smaller bullet and higher velocity.
But one major Army that was in the trenches did adopt a smaller than 9mm caliber.
Which is in the thread title. And they looked at 9mm beforehand too.
But they had the luxury of not having adopted a semi-auto handgun before the war, so weren't incentivized to keep what they had, and could look for the 'optimum' caliber.
The US didnt ditch the .45 after the trenches. And the Brits didnt even ditch revolvers! (Though they did downsize calibers, to a cartridge that is even weaker than 9mm).
The Soviets adopted a souped up version of .30 Lugers cousin.
The French replaced their hodgepodge of revolvers, C96s, and .32 ACPs of various makes, with a hot rodded .32.
The only reason they switched to 9mm post war was because the interwar defense spending was so anemic they barely got anything into service before the Germans were goosestepping through Paris, and ended up with more captured Wehrmacht equipment in stockpiles than anything homegrown.