Wainwright then promptly re-enlisted. After re-enrolling for Civil War military service at West Chester on September 23, 1861, he then officially mustered in there as second sergeant with Company F of the 97th Pennsylvania Infantry. Military records at the time described him as being a 28-year-old coach painter residing in West Chester, who was 5'7" tall with light hair, grey eyes and a light complexion. Promoted to first sergeant on October 3, 1861, he participated with his regiment in the Union Army's Expedition to Point Royal, South Carolina during the fall and early winter of 1861 and in the Union's 112-day Siege of Fort Pulaski, Georgia, which began in December 1861 and ended with the Battle of Fort Pulaski April 10–11, 1862. During this phase of service, he was commissioned as a second lieutenant on January 10, 1862.