Interwar era and World War II thumb|Suomi M31 submachine gun with 70-round drum magazine attached, 20- and 50-round box magazines As better materials became available following the First World War, light machine guns became more readily portable; designs such as the Bren light machine gun replaced bulky predecessors like the Lewis gun in the squad support weapon role, while the modern division between medium machine guns like the M1919 Browning machine gun and heavy machine guns like the Browning M2 became clearer. New designs largely abandoned water jacket cooling systems as both undesirable, due to a greater emphasis on mobile tactics; and unnecessary, thanks to the alternative and superior technique of preventing overheating by swapping barrels.
Interwar era and World War II thumb|Suomi M31 submachine gun with 70-round drum magazine attached 20- and 50-round box magazines As better materials became available following the First World War light machine guns became more readily portable; designs such as the Bren light machine gun replaced bulky predecessors like the Lewis gun in the squad support weapon role while the modern division between medium machine guns like the M1919 Browning machine gun and heavy machine guns like the Browning M2 became clearer New designs largely abandoned water jacket cooling systems as both undesirable due to a greater emphasis on mobile tactics; and unnecessary thanks to the alternative and superior technique of preventing overheating by swapping barrels