On November 12, 1861, Baird was promoted to major in the Regular Army while serving as an assistant inspector general. He became chief of staff to Maj. Gen. Erasmus D. Keyes during the first part of the Siege of Yorktown, where his service earned him a further promotion to brigadier general of U.S. Volunteers on April 30, 1862, to rank from April 28, 1862.
On November 12, 1861, Baird was upgraded to major in the Regular Army while serving as an assistant inspector general. He became chief of staff to Maj. Gen. Erasmus D. Keyes during the initial phase of the Siege of Yorktown, where his service earned him a further promotion to brigadier general of U.S. Volunteers on April 30, 1862, effective from April 28, 1862.