The M15 General Officer’s pistol was the replacement for the Colt Model M, which had long been the military issue sidearm for General-level officers. By the late 1960s, however, the supply of Model M pistols was running out, and Colt no longer had the design (the Pocket Hammerless) in production. Dale Hoffman, Superintendent of Small Arms at Rock Island Arsenal designed his own shortened (4.25 inch barrel) and accurized 1911 and submitted it to the Army unsolicited as a replacement for the Model M.
This resulted in trials in 1971, where Hoffman’s gun was put up against both steel and aluminum framed S&W Model 39s, a 9mm Colt Series 70, and a Walther P38. Hoffman’s design came out the best, and was formally adopted in 1972. Between 1972 and 1974, the Rock Island Arsenal converted 1004 stock 1911A1 pistol into M15s, and they were issued out until 1982, when the supply was exhausted. At that point, General officers began to be issued standard 1911A1 pistols, and later Beretta 92s. As an interesting side note, any General issued an M15 had the option of purchasing it from the government for $147 upon retirement – and I would presume that most took that option.