The AK-47 is a selective-fire, gas-operated 7.62×39mm assault rifle, first developed in the Soviet Union by Mikhail Kalashnikov. It is officially known as Avtomat Kalashnikova. It is also known as a Kalashnikov, an "AK", or, in Russian slang, Kalash. Design work on the AK-47 began in the last year of World War II (1945). After the war in 1946, the AK-46 was presented for official military trials. In 1947 the fixed-stock version was introduced into service with select units of the Soviet Army. An early development of the design was the AKS-47 (S—Skladnoy or "folding"), which was equipped with an underfolding metal shoulder stock. In 1949, the AK-47 was officially accepted by the Soviet Armed Forces and used by the majority of the member states of the Warsaw Pact. The original AK-47 was one of the first true "assault rifles" to be manufactured, after the original Sturmgewehr 44. Even after six decades the model and its variants remain the most widely used and popular assault rifles in the world because of its durability, low production cost, and ease of use. It has been manufactured in many countries and has seen service with armed forces as well as revolutionary and terrorist organizations worldwide. The AK-47 was the basis for developing many other types of individual and crew-served firearms. More AK-type rifles have been produced than all other assault rifles combined. Firing the 7.62x39mm cartridge, the AK-47 produces significant wounding effects when the projectile tumbles and fragments in tissue; but it produces relatively minor wounds when the projectile exits the body before beginning to yaw.