M21

The development of the M21 began during the Vietnam War to meet the requirement for a dedicated sniper weapon system. In 1968, the Marines Weapons Command, Combat Development Command, and the Limited Warfare Agency designed the system. The Rock Island Arsenal converted National Match M14 target rifles by installing an Adjustable Ranging Telescope designed by Lieutenant James Leatherwood, which integrated rangefinding and bullet drop compensation. This initial configuration, designated the XM21, was first fielded in 1969. Springfield Armory and Smith Enterprise, Inc. also manufactured the weapon. The system received the official M21 designation in 1972.

The firearm utilizes a gas-operated action with a rotating bolt. The feeding mechanism relies on detachable box magazines. Sighting systems include a National Match front blade, a match-grade hooded rear aperture with adjustments for windage and elevation, and a modified commercial variable-power telescopic sight. Early production models featured select walnut stocks, which were replaced by fiberglass stocks on the standardized M21. The glass-bedded action and the semi-permanent scope mounting system drew criticism in military evaluations because they prevented easy disassembly and maintenance under field conditions.

The weapon entered service during the Vietnam War, where the XM21 was deployed alongside day optics and night vision sights. The United States Army utilized the M21 as its primary sniper rifle from 1975 until 1988, when the military began replacing it with the bolt-action M24 Sniper Weapon System. United States Army Rangers utilized the rifle during the 1983 invasion of Grenada, and units deployed the weapon during subsequent conflicts in Iraq and Afghanistan. Other adopting nations include El Salvador, Israel, Tunisia, former user Panama, and the Philippines, where the Government Arsenal refurbishes the rifles with new optics. Known variants of the system include the M25 and the M21A5.