Firearm a battle rifle such as the Karabiner 98k, but the chief differences defining an assault rifle are select-fire capability and the use of a rifle round of lesser power, known as an intermediate cartridge. Soviet engineer Mikhail Kalashnikov quickly adapted the German concept, using a less-powerful 7.62×39mm cartridge derived from the standard 7.62×54mmR Russian battle rifle round, to produce the AK-47, which has become the world's most widely used assault rifle. Soon after World War II, the Automatic Kalashnikov AK-47 assault rifle began to be fielded by the Soviet Union and its allies in the Eastern Bloc, as well as
AK-47 of the USSR. The Soviets were impressed with the weapon and immediately set about developing an intermediate caliber fully automatic rifle of their own, to replace the PPSh-41 submachine guns and outdated Mosin–Nagant bolt-action rifles that armed most of the Soviet Army. The Soviets soon developed the 7.62×39mm M43 cartridge, the semi-automatic SKS carbine and the RPD light machine gun. Shortly after World War II, the Soviets developed the AK-47 assault rifle, which would quickly replace the SKS in Soviet service. Introduced in 1959, the AKM is a lighter stamped steel version and the most ubiquitous variant of the entire