 Hunt was promoted to colonel as the Chief of Artillery for General George B. McClellan, and Benson assumed command of Battery M.

In November 1861, Battery M was converted to a horse artillery battery, equipped with six 3-inch Ordnance rifles.In 1862 Battery M moved with the Army of the Potomac into Virginia as part of McClellan's Peninsula Campaign (March–July 1862).Benson led his unit effectively through the Siege of Yorktown, the Battle of Hanover Court House, and the Battle of Seven Pines (Fair Oaks Station).