As you may or may not be aware, most of the major powers commeced WWII with a strange mix of small arms:
Germany: Base Infantry rifle: K98K bolt action, 5 shot Cal. 8X57
Squad SMG: MP38 and later MP40 (a weapons preferred by many into the Cal. 9mmX18
Platoon of squad Mg: MG34 and later MG42 (The Bundeswehr may still be using the latter in 7.62 Nato)
Base infantry rifle(s) SMLE MkIII no 1 and SMLE (Short magazine Lee Enfield) Mk IV and V (MK five also know as Jungle Carbine) cal. .303
Squad support weapon; Sten (it is unclear when their use was common) Gun in 9mmX18
Platoon Automatic Weapon: Bren Gun (Brno-Enfield) in Cal.303
Heavy weapons: Vickers MG cal.303
Base infantry rifles:
Springfield M1903, M1903A3 later supplanted by M1 Garand (many manufacturers)
Support weapon: M1929 Thompson cal. 45 Acp and M1 Carbine in .30 Carbine.
Heavy Weavy support: BAR, M1919 Mg in Cal .30 US (.30-06) (The BAR was also used in Marine "fire teams" and as a SAW (squad automatic weapon)
In 1944 the Germans came to the conclusion that the K98k and SMG combination was inadequate. As a response to this perception they developed and deployed in limited numbers the STG 44 in 8mm Kurz (short).
It is generally agreed that the deployment (as in the case of the aircraft Me 262) of this weapon (a true assualt rifle)came too little and too late (see article in current SGN)
The Russians who commenced the war with the M1891 Moisin Nagant in 7.62 X 54 with the support of the SMG PPSH in Cal. 7.62mm (a cartridge similar to the .30 carbine) bought into the concept of the STG44 and adopted the AK47 in, well-----1947.
This weapon has heavily affected world history-and the point is it would have been ill for us had the STG 44 been properly deployed, although it did see somewhat limited use commencing in well-----1944.