Initially assigned with his regiment to picket and scout duties in Maryland and Virginia during the fall and winter of 1861, Elliott and his fellow 1st Pennsylvania Cavalrymen were then attached to the Army of the Potomac (McCall's division) in March 1862, to McDowell's I Corps in April, and then to the Union's Department of the Rappahannock (Bayard's Cavalry), during which time they fought in the Battle of Cross Keys (June 8, 1862), skirmished with the enemy at Madison Court House (July 23) and Slaughter House (August 8), fought in the battles of Cedar Mountain (August 9), Thoroughfare Gap (August 28), Second Bull Run (August 28–30), Chantilly (September 1), Antietam (September 16-17), and Fredericksburg (December 11-15).