Lackadaisy Bushwhack
Mk1 and Mk2 time fuse fragmentation grenades were a product of the Great War.  It probably goes without saying the war spurred a myriad of weapon technology advancements.  Many of those new weapons (most famously, the Thompson sub-machine gun) and surplus arms subsequently made their way, one way or another, into the culture of crime stirred up by National Prohibition.