M3 grease gun
Quite underrated. It doesn't have anything unique about it, but its as accurate as the mp40 and just as deadly.
The Stuart tank.
It can be as much a menace as the Crusader against NA German tanks. Its shape and armor make it actually harder to kill
than you imagine, and it has decent killing power until you experience Panzer IV F1s.
Not exactly a weapon, but
Smoke grenades
The sheer number of stalemates that can be broken by a good smoke screen calling down by artillery, fired from tanks or
thrown by infantry is amazing - more so amazing is how people don't realize the use. You can clear a room if you throw in
smoke, initiate a counter-attack with fewer soldiers against more defenders and flank an enemy, not to mention cover
large open areas, YET few people actually realize its immense tactical value.
m1 carbine
The master of the medium range in my opinion. The one weapon that holds its own against the STG. sure it has lower caliber,
but its range more than compensates, and it has much lower recoil for only slightly less killpower.