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.
George Armstrong Custer during the Manassas Campaign, where Army commander Winfield Scott detailed him to carry messages to Major General Irvin McDowell. After the battle, Custer continued participating in the defenses of Washington D.C. until October, when he became ill. He was absent from his unit until February 1862. In March, he participated with the 2nd Cavalry in the Peninsula Campaign (March to August) in Virginia until April 4. On April 5, Custer served in the 5th Cavalry Regiment and participated in the Siege of Yorktown, from April 5 to May 4 and was aide to Major General George B. McClellan; McClellan was