Where m and m's first created for us military?

Answer 1

Yes, because the hard outer shell prevents them from melting.

Answer 2

"M" and "M's" are often used as abbreviations for various equipment and items used by the United States military. These designations are typically assigned to identify specific models or versions of military gear, such as weapons (e.g., M16 rifle), vehicles (e.g., M1 Abrams tank), or ammunition (e.g., M9 handgun).