Colt Walker of Texas had been the major purchaser of the early Paterson Holster Pistol (No. 5 model), a five shot cal .36 revolver, and Samuel Walker became familiar with it during his service as a Texas Ranger. In 1847, Walker was engaged in the Mexican-American War as a captain in the United States Mounted Rifles. He approached Colt, requesting a large revolver to replace the single-shot Aston Johnson holster pistols then in use. The desired .44-.45 caliber revolver would be carried in saddle mounted holsters and would be large enough to dispatch horses as well as enemy soldiers. The Colt Walker
History of the New York City Police Department standard issued revolver for the NYPD. It was the Colt New Police Revolver in .32 Long Colt caliber. He also instituted required firearms training including pistol practice and qualification for officers. In 1907 the Colt Police Positive revolver in .38 caliber was adopted by the department. In May 1926 the NYPD adopted the .38 Special cartridge as the standard issue ammunition for the department and started issuing its officers the Smith & Wesson Model 10 revolver and the Colt Official Police revolver. In 1994 the NYPD replaced the revolver as its main service weapon and adopted the 9mm semiautomatic pistol