An assault rifle is a fully automatic selective-fire rifle that uses an intermediate cartridge and a detachable magazine. Assault rifles were first used during World War II. Though Western nations were slow to accept the assault rifle concept after World War II, by the end of the 20th century they had become the standard weapon in most of the world's armies, replacing battle rifles and sub-machine guns. Examples include the StG 44, AK-47 and the M16 rifle.