Horace White was 25 when he enlisted as a corporal in Co. E of the 1st Maine Cavalry, a company raised in Houlton. He enlisted on October 19, 1861.
In 1862, White was promoted to sergeant and in 1864, to first sergeant. He mustered out on November 25, 1864.
During the war, one of White's frequent correspondents was his sister Angelia, two years his senior. Horace's father, Moses, worked as a butcher. He had two older brothers, Robert and Moses.
After the war, Horace White returned to Houlton where he worked as a carpenter. In 1870, he was the head of a household that included his widowed mother, Mary L. White, and his sister Angelia.