The M1917 Revolver was a U.S. six-shot revolver

Revolver

A revolver is a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing. The first revolver ever made was built by Elisha Collier in 1818. The percussion cap revolver was invented by Samuel Colt in 1836. This weapon became known as the Colt Paterson...

 of .45 ACP

.45 ACP

The .45 ACP , also known as the .45 Auto by C.I.P., is a cartridge designed by John Browning in 1904, for use in his prototype Colt semi-automatic .45 pistol and eventually the M1911 pistol adopted by the United States Army in 1911.-Design and history:The U.S...

 caliber. It was adopted by the U.S. Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 in 1917 to supplement the standard M1911 .45 ACP semi-automatic pistol during World War I. Afterwards, it was primarily used by secondary and non-deployed troops. There were two variations of the M1917, one from Colt and one from S&W.
U.S. civilians arms companies of Colt

Colt's Manufacturing Company

Colt's Manufacturing Company is a United States firearms manufacturer, whose first predecessor corporation was founded in 1836 by Sam Colt. Colt is best known for the engineering, production, and marketing of firearms over the later half of the 19th and the 20th century...

 and Remington Rand

Remington Rand

Remington Rand was an early American business machines manufacturer, best known originally as a typewriter manufacturer and in a later incarnation as the manufacturer of the UNIVAC line of mainframe computers but with antecedents in Remington Arms in the early nineteenth century. For a time, the...

 as well as other companies were producing M1911 pistols under contract for the U.S.