The Mark 12 Special Purpose Rifle (Mk 12 SPR) entered service with the United States Special Forces in 2002 and has seen continuous use since. The weapon has been featured prominently in operations throughout the Afghanistan and Iraq theaters of war, often times in the hands of the highly-trained specialists of the U.S. Army and U.S. Navy. A prime operator of the SPR is, in fact, the U.S. Navy SEALs which dictates that the SPR be a reliable, extremely effective and robust weapon system. The Mk 12 was specifically developed for use by the Naval Surface Warfare Center Crane Division (NSA Crane) and is largely based on workings of the AR-15 / M16 pattern rifle with a few noticeable external additions and modifications.
The Mk 12 was born out of a joint U.S. Army / Navy requirement calling for a compact, semi-automatic sniper system. Multiple prototypes were considered and these were then heavily tested resulting in the finalized "Mk 12" form. As in the AR-15 and M16, the Mk 12 is chambered 5.56x45mm NATO but the cartridges themselves are specially-developed for the Mk 12's semi-automatic, gas-operated rotating bolt action system. The weapon feeds from a 20- or 30-round detachable box magazine and, more or less, retains the AR-15/M16's form and function in-the-field. Effective range is listed out to 600 yards with a muzzle velocity nearing 3,050 feet-per-second. The pistol grip is ergonomically grooved for a firm hand hold while the trigger is set within an integrated guard. The magazine well is located just ahead of the trigger unit in conventional fashion.
The forend is made up of a perforated, tubular handguard to which an accessories rail section is affixed along the forward lower face - this allows use of a collapsible bipod for steady firing. The upper portion of the receiver and the forend also sport a rail system for the use of tactical accessories and optics as needed. The shoulder stock extends from a collapsible tubular frame and helps the operator achieve a stable four-point firing position (both hands, a bipod and the shoulder stock) for maximum accuracy at distance. The barrel protrudes only a short distance from the forend and is capped by a single-baffled muzzle brake. The barrel measures 18 inches in length while overall length of the SPR weapon is 37.5 inches. A fully-loaded rifle weighs 10lb, slightly more than the original M16. In comparison, the M16 measures in at 39.5 inches long with a 20-inch barrel length.
There are several notable iterations of the Mk 12 in circulation: the "Mk 12 Mod 0" is used by Army special forces and "Mk 12 Mod 1" is used by Navy special forces. The formal "long designation" for the rifle is "United States Navy Mark 12 Mod 0/1 Special Purpose Rifle".