Colt's answer to this call was a new version of their New Service Model revolver. Most sources agree that the Colt M1917 is an alteration of their 1909 New Service Model.
While both Colt's and Smith & Wesson's 45 ACP revolvers were designated M1917, were stamped U.S. Army Model 1917, and share other similarities, they are distinctly different guns.
Shown in the photo is a Colt M1917 Army revolver, manufactured around 1920. Stamped on the left side of the barrel is "COLT D.A. 45." On the left side of the frame, just forward of the hammer, an inspector's mark is stamped - an eagle head with "SI5" or "S15" below. Colt's trademark rearing-colt emblem is stamped on the left side of the frame (it's actually the frame sideplate), above and just forward of the top of the left grip panel.
Opening the cylinder reveals the gun's serial number, which is stamped on the frame near the crane and also on the inside of the crane itself. Above the serial number on the frame is an H, and below it is an F.
The same H is found stamped on the rear face of the cylinder, and on the bottom rear of the barrel. It has been said that the H stampings found on this gun and others like it is the inspection mark of Francis L. Hosmer.