 Promoted to major, he was part of an expedition that was sent to Florida to quell the rebellion in that state, but was taken as a prisoner of war at Fort Pickens in October 1861 during the Battle of Santa Rosa Island.After being exchanged in August 1862, he was appointed as a brigadier general in the Union Army's X Corps in November 1862.He commanded the Federal forces on Folly Island beginning in August 1863 and participated in the Second Battle of Charleston Harbor.