The first M-1 Garands used in combat was by the 31st Infantry Regiment on Luzon, PI, in December, 1941, is one of the tidbits of history I learned from the US Army Center of Military History while working there. The sending of several thousand M-1’s to the Philippines during either late 1940 or early 1941 was one of the modernization of the US Army’s Philippine Division.
Marines were slow because they trained with a tried a true weapon and the commanders new a war was coming. Thats what I’ve read before. But show a marine an advantage they will adapt. John Garand showed the army his rifle chambering a 277 caliber. The marines and Army told him it was the wrong caliber. He came back with a .30/3006. They army took it the marines true to their reputation were a little skeptical. They aren’t to stupid(contrary to idiots that don’t know them) to figure things out. History is made and the boys are still MAGA.