American military technologies developed during World War II became more advanced and specialized as the war progressed. The technologies produced ranged in complexity from relatively simple items such as small arms and armored vehicles, including tanks, to more complex items such as the atomic bomb. The latter, produced under the secretive Manhattan Project, proved to be an incredibly powerful weapon that revolutionized warfare and was used to end the war. Other technologies, such as the M4 Sherman tank, the M1 Garand and M1 Carbine, and the gas mask, were refinements on previously existing technologies.