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 had written to Johnson some weeks before seeking such a commission. Custer and his wife stayed with the president during most of the trip. At one point Custer confronted a small group of Ohio men who repeatedly jeered Johnson, saying to them: "I was born two miles and a half from here, but I am ashamed of you." On July 28, 1866, Custer was appointed lieutenant colonel of the newly created 7th Cavalry Regiment, which was headquartered at Fort Riley, Kansas. He served on frontier duty at Fort Riley from October 18 to March 26, and scouted in Kansas and