High Quality Content by WIKIPEDIA articles! The AR-18 is a gas operated, selective fire assault rifle chambered for 5.56x45mm ammunition. 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, its production licence was sold to companies in Japan and England, and it is said to have influenced many later weapons such as the British SA80, the Singaporean SAR-80 and SR-88, the Austrian Steyr AUG, and the Heckler and Koch G36. It gained some notoriety through its use by the Provisional IRA, which allegedly christened it the "Widowmaker".