| Unit Name: | 1st Marine Amphibious Corps |
| Dates: | 1 October 1942 to 15 April 1944 |
| Country: | United States |
| Branch: | USMC |
| Battles: | Invasion of Bougainville |
The I Marine Amphibious Corps, or I MAC, was a formation of the United States Marine Corps.It was created on 1 October 1942, with most of the staff transferred from Amphibious Corps, Pacific Fleet (ACPF). It was then deployed to the South Pacific Areaa U.S.-led multinational military command active during World War II that was a part of the U.S. Pacific Ocean Areasfirst to Hawaii, then to New Caledonia.[1]
When the Marine Corps was not satisfied with the leadership of its commander, Major General Clayton B. Vogel, Commandant Thomas Holcomb ordered Alexander Vandegrift to take command. Vandegrift, the commander of the 1st Marine Division during the Battle of Guadalcanal was promoted to lieutenant general.[2]
General Vandegrift carried on in command of the Corps when its next-designated commander for the invasion of Bougainville, Major General Charles D. Barrett, died following a fall from the balcony of his quarters in New Caledonia.[3] General Vandegrift led I MAC during the invasion and was later made the Commandant.
The Corps consisted of the 3rd Marine Division, the 37th Infantry Division (United States), the 8th Brigade (New Zealand) and the 53rd Naval Construction Battalion (Seabees). It conducted the invasion of Bougainville. When the 53rd was assigned to the Marine Corps it was redesignated "Naval Construction Battalion First Marine Amphibious Corps"[4]
On 15 April 1944, I MAC was renamed the III Amphibious Corps.[5]
The Corps' insignia was a shield with a blue field emblazoned by the Southern cross constellation in white and a square red diamond outlined with a white border, center. Various elements of the Corps used this basic design with their task insignia in white on the red center.