pretty hard to crank out high numbers in an unheated factory at 30 below and dodging bombs.

At least the US has stayed to one system; T for test or made for export only (T-16 = US Bren, T-17 E1/E2 = Staghound)and M for standardized vehicle. That makes it a bit easier.

What is more confusing is the British unit marking system of military vehicles. US is simple, German is a bit more complex but is very logical, with a little confusion between different HQ, (ie; SS or Wehmacht, or STU) Japanese, no standard system, Russians had none other than crew applied political grafitti, but the British [:@][:@]