Assault rifle

An assault rifle is a selective fire rifle that uses an intermediate cartridge and a detachable magazine.[1][2][3][4][5] Assault rifles were first put into mass production and accepted into widespread service during World War II. The first assault rifle to see major usage was the German StG 44, a development of the earlier Mkb 42.[6][7][8] While immediately after World War II, NATO countries were equipped with battle rifles, the development of the M16 rifle during the Vietnam War prompted the adoption of assault rifles by the rest of NATO. By the end of the 20th century, assault rifles had become the standard weapon in most of the world's armies, replacing full-powered rifles and sub-machine guns in most roles.[8] Some of the most successful assault rifles include the AK-47, M16, IMI Galil and Heckler & Koch G36.

The StG 44 was adopted by the Wehrmacht in 1944. It fires the 7.92×33mm Kurz round.
Currently the most used assault rifle in the world along with its variant, the AKM, the AK-47 was first adopted in 1949 by the Soviet Army. It fires the 7.62×39mm M43 round.
The M16 was first introduced into service in 1964 with the United States Armed Forces. It fires the 5.56×45mm NATO cartridge, and is the most produced assault rifle in its caliber.