[1][2] Upon joining the Army, he served in the Dakota Territory as a sergeant with Company M, 3rd Cavalry Regiment, during the Great Sioux War of 1876–77.

[1] 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.

Kirkwood and two other men, Blacksmith Albert Glawinsky and Sergeant Edward Glass, attempted to dislodge the Indians from the ravine but were turned back.

[1] Kirkwood's official Medal of Honor citation reads: Bravely endeavored to dislodge some Sioux Indians secreted in a ravine.

[1]In 1920, Kirkwood returned to Slim Buttes, near present-day Reva, South Dakota, and helped place a monument commemorating the battle.