He was a staff officer during the liberation of the Upper Mississippi, and then served in the front line at Corinth and Vicksburg, being promoted to brigadier general.

He is chiefly remembered for his stubborn defense of the Allatoona Pass in October 1864 against superior numbers, despite being seriously wounded, while Maj. Gen. William T. Sherman signalled a message which was turned into a popular ballad Hold the fort, for I am coming.

His father, John Lockwood Corse, served six terms as the mayor of that town and established a prosperous book and stationery business.

Leaving West Point in 1855, Corse chose not to stay in the military, but instead attended a law school in Albany, New York, and passed his bar exam.

Assigned command of the 4th Brigade, 4th Division, XV Corps, in the Federal Army of the Tennessee, Corse participated in the Chattanooga Campaign.

After recuperating from an injury suffered at Missionary Ridge, Corse returned to active duty as the inspector general on Maj. Gen. William Tecumseh Sherman's staff.

On Sherman's orders, Corse went with 2,100 men to secure Allatoona Pass to prevent Confederate Gen. John Bell Hood from severing Union communications.

During the bloody battle, Corse "lost one third of his men and one third of his ear" but secured the pass on October 5, the date on which he was later appointed a brevet major general.