http://en.wikipedia.org/wiki/AR-18

The AR-18 was designed at ArmaLite in California by Arthur Miller, George Sullivan, and Charles Dorchester in 1963 as an improved alternative to the AR-15 design, which had just been selected by the U.S. military as the M16. While the AR-18 was never adopted as the standard service rifle of any nation, it is said to have influenced many later weapons such as the British SA80,[1] the Singaporean SAR-80 and SR-88, and the Heckler and Koch G36. It gained some notoriety through its use by the Irish Republican Army (IRA)