Keifer enlisted in the
3rd Ohio Infantry, a three-months regiment, being appointed major. He served in
western Virginia fighting in the battles of
Rich Mountain and
Cheat Mountain and afterward was promoted to lieutenant colonel of the regiment. When his term expired, he joined the
110th Ohio Infantry and became its
colonel. He served in the
Eastern Theater leading his regiment at the
second battle of Winchester. While the Union army was soundly defeated and most of it surrendered, Keifer's regiment was able to avoid capture. Following the battle of Gettysburg, Keifer was assigned to brigade command in the
III Corps and fought at the
battle of Wapping Heights. After Robert E. Lee's army had retreated to safety in Virginia, Keifer and his regiment were dispatched to New York City to help suppress the
draft riots. Keifer returned to the Army of the Potomac in time for the
Overland Campaign. He was wounded in the arm at the
battle of the Wilderness, putting him out of action for a time. When he did return to active duty he was placed in command of the 2nd Brigade in
James B. Ricketts's 3rd Division of the
VI Corps. He led his brigade at the battles of
Winchester and
Fisher's Hill. During the
battle of Cedar Creek, VI Corps commander
Horatio G. Wright temporarily commanded the Army of the Shenandoah and Ricketts temporarily in command of the corps. This put Keifer in command of the 3rd Division in Ricketts's absence. When
Philip H. Sheridan heroically returned to command the army in the midst of the battle, returning Wright to corps command, Ricketts had already been wounded, leaving Keifer in command of the division for the rest of the battle. For his service during the Shenandoah Valley Campaign, on December 12, 1864,
President Abraham Lincoln nominated Keifer for appointment to the grade of
brevet brigadier general of volunteers, to rank from October 19, 1864, and the
United States Senate confirmed the appointment on February 14, 1865. When the VI Corps returned to the Army of the Potomac General
Truman Seymour was placed in command of the 3rd Division and Keifer returned to command the 2nd Brigade, taking part in the
breakthrough at Petersburg and the
Appomattox Campaign. Keifer was breveted as a major general, to rank from April 9, 1865, in recognition of his contributions to the campaign. ==Political career==