my viewpoint is the American forces were planning on new automatic rifle in 1940s but having the country cut in half caused rifle development to be lowest priority during the war. Thompsons may have been in use 1941 but how long would it have take for them to be produced in enough numbers to equip every unit with. the automatic rifle at the end of great war may have been scrapped so that the army could save money by not having to buy two different weapons during peacetime.