Organized in Apr. 1944 of elements of the 1st MAC to direct the operation of two Marine Amphibious Corps in the pacific theater. The combat elements of 1st MAC fell under IIIAC while a short time later, the administrative and support elements came under the purview of FMFPAC.  Elements of this unit fought on Saipan, Tinian, Guam,  Peleliu, and Okinawa. Following the Japanese surrender this Corps saw occupation duty in Northern China in Oct. 1946, as Marine Forces China.

Established 4 Sept. 1943 from the redesignated Headquarters, Amphibious Corps Pacific Fleet, as a augment to the 5th Fleet and Central Pacific Force Naval commands. This unit was tasked the mission of combining and directing Marine Corps and Army amphibious assaults. VAC units went ashore on Tarawa and the Army assault of Makin Island. (Not the Raider mission of earlier in the war.) Additional action was seen at Kwajalein, Eniwetok, the Marianas, Saipan, Tinian, Guam, the Philippines, Iwo Jima, and the occupation of Japan.