Mitchell then re-enlisted for another tour of duty — this time for a three-year term of service. After re-enrolling on September 9, 1861 in Brookville, he then re-mustered in Pittsburgh as a sergeant with Company A of the 105th Pennsylvania Infantry under his former commanding officer from the 8th Pennsylvania. Alex Mitchell's younger brother, James, also mustered in with him that same day, joining the same company of the 105th Pennsylvania as a drummer boy. Ordered again to defensive duties near Washington, D.C. in early October, Mitchell and his fellow 105th Pennsylvanians were transported south by railroad, and pitched their tents at Camp Kalorama on the Kalorama Heights outside of Georgetown, District of Columbia before relocating again — this time to Alexandria, Virginia, where they were assigned to the brigade led by Brigadier-General Charles Davis Jameson in the U.S. Army division commanded by Brigadier-General Samuel P. Heintzelman. On November 8, Mitchell was promoted to the rank of first sergeant. Reassigned to duties at Fortress Monroe on March 17, 1862, he and his regiment then engaged in their first significant combat during the Siege of Yorktown (April 5–May 4) and the Peninsula Campaign (March–July 1862), including the battles of Williamsburg (May 5) and &lt;a href="Battle%20of%20Fair%20Oaks"&gt;Fair Oaks/Seven Pines&lt;/a&gt; (May 31), during which Mitchell was wounded in action. Reporting later on the battle, Jameson described how the day’s events unfolded: