The Thompson was used by American soldiers. Captain Miller, Sergeant Horvath, Captain Hamill and Corporal Henderson used this submachine gun. It uses a .45 caliber bullet and was one of the most reliable machine guns of the war. The large .45 caliber bullet was amazing and more powerful than the German 9 millimeter MP40, thus giving it a deadly and feared reputation, and was made by John T. Thompson. It was later replaced by the M3 grease gun to some extent in 1943, but was still used as the main sub-machine gun by American Soldiers in the Normandy Invasion of World War 2 in 1944. Since the Grease gun was adopted, more people used M3 Grease Guns, but the Thompson was still the primary Sub Machine Gun.