Shortly after the United States entered World War I, the regiment was constituted in the National Army on 18 May 1917 and organized on 30 March 1918 at Fort D.A.

At the time, regimental units were scattered over Rhode Island, eastern Massachusetts, and southern Vermont and New Hampshire.

[2] The 315th's Rhode Island units usually held their inactive training period meetings at Providence's Armory of Mounted Commands.

At the latter, Vermont and New Hampshire units of the regiment conducted annual contact camps in the fall or winter.

[2] After the United States entered World War II, most of its personnel were called up for active duty[3] and the regiment was disbanded on 18 October 1943.

The colors were those of the 64th Cavalry Division, the seahorses represented the seafaring heritage of New England, where it was based, and the motto was given to the regiment by its first Regular Army instructor, Colonel Francis Marshall.

The regimental coat of arms included a golden shield divided by a black stripe with a red rooster in the upper right and a winged thunderbolt in the lower left.