During World War II, III MEF was known as I Marine Amphibious Corps. It was renamed III Amphibious Corps on 15 April 1944, and took part in fighting against the Japanese Empire in the Pacific theater during World War II. It fought in some of the bloodiest battles, including the Solomon Islands campaign, the Mariana and Palau Islands campaign and the Volcano and Ryukyu Islands campaign (namely the Battle of Okinawa). III Amphibious Corps redeployed to Tientsin, China, in September 1945, where it participated in the occupation of Northern China until June 1946. III Amphibious Corps was deactivated on 10 June 1946.