On August 9, 1861, Martindale was commissioned a
brigadier general of volunteers in the Union Army, and was assigned to command a brigade within the Union
Army of the Potomac. He later participated in all the battles of the
Peninsula Campaign in
V Corps. After the retreat from
Malvern Hill, he was brevetted a
major general of volunteers, and appointed
Military Governor of Washington, D.C., a post he held from November 1862 to May 1864. Afterward, he returned to field service, fighting with the
XVIII Corps in the
Bermuda Hundred Campaign, the
Battle of Cold Harbor and the
Siege of Petersburg, commanding the corps briefly in mid-July 1864. In September 1864, he resigned his commission because of bad health. ==Return To Post-War Life==