US Marine Corps Pacific Theater of Operations 1943–44

The US Marine Corps (USMC) was one of three components of the wartime Navy Department, the others being the US Navy (USN) and US Coast Guard. On January 1, 1944 LtGen Alexander A. Vandegrift, former Commanding General, I Marine Amphibious Corps (IMAC), became the 18th Commandant of the Marine Corps, assuming the duty from LtGen Thomas Holcomb.

The USMC was subdivided into two broad organizations: the Fleet Marine Force (FMF); and the Shore Establishment, plus Headquarters, Marine Corps (HQMC) in Arlington Annex, Navy Department, Washington, DC. The FMF contained the Corps' operating elements: ground combat, aviation, service, and most training units. The Shore Establishment included Marine Corps schools, supply depots, recruiting stations, recruit training depots, and Marine barracks and detachments guarding naval bases, stations, and depots.

By January 1944 the Marine Corps had grown to 28,193 officers, 10,723 officer candidates, and 366,353 enlisted Marines, with a total of 405,169 personnel: of these, 10,430 were female. The FMF had grown to two amphibious corps, four divisions (with a fifth about to be activated), a separate infantry regiment, 19 defense battalions, and numerous support and service units: the total number of Marines and sailors in ground units was 199,324. Marine Aviation had grown to four aircraft wings, 21 groups, and 88 squadrons, totaling 91,075 personnel.