The Colt Model 1910 was a prototype .45 ACP caliber automatic pistol developed by John Browning as an improvement of the earlier Colt Model 1909, which was rejected by the United States Department of War due to the Cavalry's belief that the design was too complicated for use by enlisted men, and because it lacked a safety mechanism.The M1910 was a drastic modification on Browning's part, modifying and adding many features that the M1909 was not equipped with.