During the Vietnam War, the United States Army sought to field a new, dependable sniper rifle. The “XM21” sniper rifle was developed jointly by the Army Weapons Command at Rock Island, Combat Development Command at Ft. Benning, and the Limited Warfare Agency at Aberdeen during late 1960s. The XM21 is essentially a converted M14 National Match rifle with the addition of a Leatherwood 3–9x Adjustable Ranging Telescope (ART) telescopic sight. The M14 was selected as the rifle’s platform due to its impressive accuracy, reliability, and ability for quick follow-up shots. Chambering the 7.62x51mm NATO round - which was developed for sniping and long range match shooting - the M21 was accurate to 750 yards (690m). The ART telescope featured a variable magnification power from 3X to 9X, allowing adjustments for targets ranging between 300m and 900m. In 1975 the XM21 was adopted as the M21 Sniper Weapon System and remained the Army's official sniper rifle until 1988, when it was supplanted by the bolt-action M24 Sniper Weapon System. The M-21 still remains in service however and has seen extensive combat in Iraq and Afghanistan.