Henry Lee Higginson entered the Union Army in May 1861, as second lieutenant of Company D in Colonel George H. Gordon's 2nd Massachusetts Regiment, and fought at the First Battle of Bull Run. He was commissioned major in the 1st Massachusetts Cavalry in March 1862. In the Battle of Aldie (1863) Higginson was knocked from his saddle and received three saber cuts and two pistol wounds. While recovering in Boston he married Ida Agassiz, daughter of Harvard professor Louis Agassiz, on December 5, 1863. Though he retired from the military as a colonel, he was commonly addressed as "Major" for the rest of his life to avoid confusion with his older cousin Thomas Wentworth Higginson, who was called Colonel Higginson.