By the early 1990s, most M1911A1s had been replaced by the Beretta M9, though a limited number remain in use by special units. The U.S. Marine Corps (USMC) in particular were noted for continuing the use of M1911 pistols for selected personnel in MEU(SOC) and reconnaissance units (though the USMC also purchased over 50,000 M9 pistols.) For its part, the United States Special Operations Command (USSOCOM) issued a requirement for a .45 ACP pistol in the Offensive Handgun Weapon System (OHWS) trials. This resulted in the Heckler & Koch OHWS becoming the MK23 Mod 0 Offensive Handgun Weapon System (itself being heavily based on the 1911's basic field strip), beating the Colt OHWS, a much-modified M1911. Dissatisfaction with the stopping power of the 9 mm Parabellum cartridge used in the Beretta M9 has actually promoted re-adoption of pistols based on the .45 ACP cartridge such as the M1911 design, along with other pistols, among USSOCOM units in recent years, though the M9 has been predominant both within SOCOM and in the U.S. military in general. Both U.S. Army Special Forces Units and SFOD-D continue to use modernized M1911s.