Colt New Service Model M1917, Us Army Model of 1917, Blue 5 1/2" US WWI Double Action Revolver, MFD 1918

 
Colt came out with their large framed double action New Service revolver in 1898.
The Army was looking for a large caliber double action pistol to replace their .38 caliber S&W and Colt pistols that had proved to have inadequate stopping power during the Philippine-American war, and adopted the New Service revolver chambered in .45 Colt in 1909.
Later, the gun was chambered in .45 ACP and called the Model of 1917. This is a M1917 revolver that has been only partially refinished and is still plenty attractive for a 1918 gun.  It is very hard to beat a .45 ACP for knockdown power