Thomas Mower McDougall subsequently he was appointed Captain, 15 Dec 1875. In 1876 Captain McDougall commanded Company B and accompanied the 7th Cavalry Regiment, under command of Lt. Col. George A. Custer in its fateful departure from Fort Abraham Lincoln to participate in what became known as the Great Sioux War of 1876, which culminated in the Battle of the Little Bighorn, also known as Custer's Last Stand which occurred on June 25–26, 1876. On May 17, 1876, the 7th Cavalry left their base at Fort Abraham Lincoln near present day Mandan, North Dakota to join in a campaign against the Sioux Indians.
Great Sioux War of 1876 To combat the Sioux the U.S. army had a string of forts ringing the Great Sioux Reservation and unceded territory. The largest force arrayed against the Indians at one time was in summer 1876 and consisted of 2,500 soldiers deployed in the unceded territory and accompanied by hundreds of Indian scouts and civilians. Many of the soldiers were recent immigrants and inexperienced on the frontier and in Indian warfare. Cavalry soldiers were armed with .45 caliber, single-action revolvers and the Springfield Model 1873, a single-shot, breech-loading rifle which gave the soldiers a large advantage in range over most Indian weapons.