The IV Corps, Army of the Potomac, was created on March 13, 1862, and placed under the command of Erasmus D. Keyes, who had commanded a brigade at First Bull Run. It consisted initially of three divisions, under Darius N. Couch, Silas Casey, and William F. "Baldy" Smith. Couch's division was transferred to join VI Corps during the Antietam Campaign and remained with them for the duration of the war. The corps' peak strength (in early 1862) was 37,000 men.