The following is from the book, Indian Wars, by Bill Yenne.
Another incident a year later would involve the man whose name is synonymous with the Indian War history of Montana. Lieutenant Colonel George Armstrong Custer was riding with ten companies of his 7th Cavalry as part of a large force under Colonel David Stanley. Custer was with Captain Myles Moylan and a small advance party on August 4, 1873, when a small group of Lakota swept into their camp near the mouth of the Tongue River, planning to steal horses, decoy troops into an ambush, or both. Custer who gave chase and was abruptly surrounded by an estimated three hundred warriors. He scampered back to Moylan's encampment and they formed a defensive perimeter. After several hours and a failed attempt to start a grass fire to smoke out the troopers, the Indians broke off the attack. The regimental veterinarian and two other soldiers were killed.
A week later, the 450-man 7th Cavalry contingent was camped near the mouth of the Bighorn River when they were surprised by an early morning attack from approximately the same number of Lakota-although Custer later reckoned there were a thousand.