 He remained in England until October 1942, when he returned to the United States to become a member of the Staff of the Commander-in-chief, U.S. Fleet, Navy Department, Washington, D.C., as Chief, Future Plans Section.In June 1943, Colonel Hart was ordered to the 4th Marine Division where he assumed command of the 24th Marine Regiment.During the following year he led the regiment in the attack on Roi-Namur, Kwajalein Atoll, Marshall Islands, where he was awarded the Navy Cross, and the assault on Saipan and Tinian and the Marianas Islands, where he was awarded the Legion of Merit.