The June 21, 1860, letter from the War Department that ordered Myer to organize and command the new U.S. Army Signal Corps provided little of substance. It authorized $2000 for equipment and a promotion for Myer to major, effective June 27. Myer was faced with the responsibility of recruiting subordinates who could be detailed from elsewhere in the Army. The Signal Corps would not commence as an official Army organization until March 3, 1863, at which time Myer was promoted to colonel. Between these two dates, Myer served first under Maj. Gen. Benjamin Butler at Fort Monroe, Virginia, where he established a camp of instruction, and then as the chief signal officer for Maj. Gen. George B. McClellan's Army of the Potomac in its campaigns from the Peninsula Campaign to the Battle of Antietam. During this period Myer was awarded a brevet promotion to lieutenant colonel in the regular army for his actions at Hanover Court House, and to brevet colonel for Malvern Hill.