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.
Battle of Stony Lake but having failed to surprise him, the Sioux probed for weak spots. Colonel James H. Baker's 10th Minnesota Regiment was in Sibley's van and advanced, firing volleys and supported by two mountain howitzers. The Sixth Minnesota and Seventh Minnesota Regiments deployed to the left and right of Sibley's wagon train. Charges by companies of infantry dislodged the Indians from several hills. Shortly, the Sioux gave up the battle and faded away. Sibley was unable to pursue them as his horses and men were tired. Sibley did not suffer any casualties. Sioux casualties are unknown, but probably light. Three Indians were