The Battle of Birch Coulee occurred September 2–3, 1862 and resulted in the heaviest casualties suffered by U.S. forces during the Dakota War of 1862. The battle occurred after a group of Dakota warriors followed a U.S. burial expedition, including volunteer infantry, mounted guards and civilians, to an exposed plain where they were setting up camp. That night, 200 Dakota soldiers surrounded the camp and ambushed the Birch Coulee campsite in the early morning, commencing a siege that lasted for over 30 hours, until the arrival of reinforcements and artillery led by Colonel Henry Hastings Sibley.