The Model 1917 IS a Colt New Service. During WW1 the U.S. military asked both Colt and S&W if they could provide revolvers chambered for the .45 ACP cartridge since Colt, Remington, and Springfield Armory were maxed out on 1911 semiauto production. Colt used the New Service as the basis for its .45 ACP revolver, and S&W used their large-frame Hand Ejector 2nd Model as the basis for theirs. The military referred to both guns as Model of 1917 Revolvers.
There's an earlier military Colt revolver known as the Model of 1909 that looks an awful lot like a 1917, but is chambered for a round similar, but not identical, to the .45 Colt cartridge.