Part of Sickles' Excelsior Brigade, the 72nd New York participated in many of the war's most significant battles. Transported to Washington, D.C., the members of this regiment were initially attached to Division of the Potomac (Sickles' Brigade), and assigned to defend the city before participating in the Union Army's expedition to lower Maryland (September 15–October 2, 1861). They were then reassigned as Sickles' Brigade to the U.S. Army of the Potomac in October as part of the division commanded by Brigadier-General Joseph Hooker. Their next significant deployment came as part of the U.S. Army's Third Corps, Second Division when they engaged in the Union Army's advance on Manassas, Virginia (March 10, 1862), the expedition from Dumfries to Fredericksburg, capture of stores (March 18), and reconnoissance from Liverpool Point to Stafford Court House and subsequent operations there (April 4). Reassigned to the Peninsula Campaign, they then participated in the Siege of Yorktown, Virginia (April 5–May 4, 1862), and incurred heavy casualties in the Battle of Williamsburg (May 5). By the time that battle was over, nearly 200 members of the regiment had been killed or wounded, a loss rate which the regiment would not experience again for the remainder of the war. Next engaged in the &lt;a href="Battle%20of%20Seven%20Pines"&gt;Battle of Seven Pines/Fair Oaks&lt;/a&gt; (May 31–June 1), the regiment then fought in the Seven Days Battles at Oak Grove (June 25), the Peach Orchard and Savage's Station (June 29), White Oak Swamp and Glendale (June 30), and Malvern Hill (July 1 and August 5). Transferred from the Peninsula during the fall of 1862, the regiment saw heavy action in the Union's Manassas Station Operations (August 25–27) and the Second Battle of Bull Run (August 28–30).