The SPR is used by the U.S. Army as well as the U.S. Navy. It is a heavily modified Marksmen variation of the AR15/M16 line of weapons. The SPR concept was originally proposed by Mark Westrom, currently president of Armalite, while working at Rock Island Arsenal. The program was an outgrowth of the desire by both US Army and Navy special operations forces for a rifle with greater effective range than an M4 Carbine but still shorter in length than a standard issue M16A2/A4. The SPR program appears to have grown out of both the SOPMOD Block II program, and the U.S. Navy SEALs 'Recon Rifle' (a 16" flat-topped AR-15/M16 Carbine). The Naval Surface Warfare Center, Crane Division (often referred to as NSWC-Crane or "Crane") essentially expanded on the Recon Rifle, an expansion that some SEALs ma