As a 19-year old, Gilman enlisted on 6 Oct 1849 in Boston, MA with Co. A, US Engineers, as an engineer at the West Point Military Academy. He was discharged, with a rank of artificer, in Newburgh, NY on 16 Apr 1852. A month prior to his discharge, he had married Sarah Elizabeth Cook of Salem, NH.
He returned to Salem, and to his employment as a shoemaker. He would also start a waltzing school with Kimball Poor of Atkinson.
He enlisted on 27 April 1861 with Company K, First New Hampshire Volunteers, and was commissioned captain on the 30th. Being only raised for three months, he was discharged on 9 Aug '61. Following his mustering out, he quickly recruited Company C of the 4th NH Infantry, and was mustered in as its captain on 18 Sept 1861. The following May, he was promoted to Lieut. Col. of the regiment. In Nov 1863, due to poor health, he had to resign his position, and returned to Salem, NH. He died there from consumption on 22 Oct 1864.
The G.A.R. post for Salem, No. 60, was named after Lt. Col. Sleeper in 1881. When the Sons of Union Veterans camp was organized in 2006, they requested the use of the "No. 60" in their name, honoring both the veteran and former Grand Army Post.
Hutchinson, John G. Roster, Fourth Regiment New Hampshire Volunteers: Photo of Col. Sleeper, pg 65; Bio, pg 78
Poor, Alfred. Historical and Genealogical Researches and Recorder of Passing Events of Merrimack Valley, Volume 1, pg 108
Rockingham County Probate: File #13517 (father David's probate)
Rockingham County Deeds: Vol. 336, pg 366 (Gilman and siblings sell land in Kingston)