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 actually been a village of Northern Cheyenne (led by Old Bear, Two Moons and White Bull) with a few Oglala (led by He Dog.) In the late spring of 1876 a second, much larger campaign was launched. From Fort Abraham Lincoln marched the Dakota Column, commanded by General Alfred Terry, with 15 companies or about 570 men, including Custer and all 12 companies of the Seventh Cavalry. The Montana Column, commanded by Colonel John Gibbon, departed Fort Ellis. General Crook commanded a third column that departed Fort Fetterman to head north. The plan was for all three columns to converge