Sunday, September 14, 1862
The Twentieth Massachusetts departed from Frederick City this morning in pursuit of the Confederate Army which was now concentrating near the town of Sharpsburg at Antietam Creek. By evening the regiment made camp near Middletown. The Second Corps, of which the Twentieth Massachusetts was a part, was not involved in today's Battle of South Mountain, a series of attacks to clear the mountain passes in Maryland for the pursuit of the Confederate Army.
Several officers did not make the journey to Antietam with the regiment. Henry Abbott, recently promoted to Captain on August 29, and Lieutenants James Murphy, and Robert Beckwith remained at Frederick City due to illness. Captain George Macy returned to Washington for additional recruits for the regiment.1
1George A. Bruce, The Twentieth Regiment of Massachusetts Volunteer Infantry 1861 - 1865 (Cambridge, Massachusetts: The Riverside Press, 1906), 154-5.