It's also the same as saying M 1 in US parlance.
M1 Combat Car/M1A2 Light Tank
M1 81mm Mortar
M1 Submachine Gun (simplified Thompson variant, quickly replaced by the even simpler M2)
And the list goes on and on...
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.