The 15th New Hampshire Infantry was organized in Concord, New Hampshire, October 6–16, 1862, and mustered in for nine months' service under the command of Colonel John W. Kingman.
It was attached to Sherman's Division, Department of the Gulf, to January 1863.
1st Brigade, 2nd Division, XIX Corps, Army of the Gulf, to July 1863.
2nd Brigade, 3rd Division, XIX Corps, to August 1863.
Moved from Carrollton to Camp Parapet, Louisiana, January 28, 1863, and served duty there until May.