In the early morning hours of September 9, 1876, two and a half months after George Armstrong Custer's defeat at the Battle of the Little Bighorn, Kirkwood was among 150 soldiers who launched an attack on a Sioux encampment of 35 lodges. The engagement would come to be known as the Battle of Slim Buttes. Early in the attack, Lieutenant Adolphus H. Von Luettwitz was shot in the right kneecap. After another man applied a tourniquet to the officer's leg, Kirkwood carried him over a ridge to safety; Von Luettwitz would survive, although his leg had to be amputated. The soldiers then raided the Sioux village, taking horses and food and discovering artifacts from the previous Battle of the Little Bighorn, including Custer's battle flag. Many of the Sioux retreated to a deep, wooded ravine south of the village and continued firing on the soldiers. Kirkwood and two other men, Blacksmith Albert Glawinsky and Sergeant Edward Glass, attempted to dislodge the Indians from the ravine but were turned back. In the process, Kirkwood was shot in the side and Glass was severely wounded in the arm; Kirkwood's injury proved to be not serious. For these actions, he was awarded the Medal of Honor a year later, on October 16, 1877.