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 be given to the resisting northern bands. In October 1876, Army troops surrounded the villages of Red Cloud and Red Leaf. They arrested and briefly confined the leaders, holding them responsible for failing to turn in individuals arriving in camp from hostile bands. The US sent another commission to the agencies. According to historian Colin Calloway, "Congress passed a law extinguishing all Lakota rights outside the Great Sioux Reservation." Colonel Ranald S. Mackenzie and his Fourth Cavalry were transferred to the Department of the Platte following the defeat at the Little Bighorn. Stationed initially at Camp Robinson, they formed the