During World War II, General Hart was awarded the Navy Cross while commanding the 24th Marines in the assault and capture of Roi-Namur Island, Kwajalein Atoll, and was awarded the Legion of Merit while leading the regiment in the battles for Saipan and Tinian in the Marianas Islands. As assistant division commander, Fourth Marine Division, during the assault at Iwo Jima, he was awarded the Bronze Star.