United States Marine Corps Order of Battle (December 1941)

Between the World Wars, the Marine Corps was headed by Commandant John A. Lejeune, and under his leadership, the Corps studied and developed amphibious techniques that would be of great use in World War II. Many officers, including Lieutenant Colonel Earl Hancock "Pete" Ellis, foresaw a war in the Pacific with Japan and undertook preparations for such a conflict. Through 1941, as the prospect of war grew, the Corps pushed urgently for joint amphibious exercises with the Army and acquired amphibious equipment that would prove of great use in the upcoming conflict.

In World War II, the Marines performed a central role in the Pacific War, along with the U.S. Army. The battles of Guadalcanal, Bougainville, Tarawa, Guam, Tinian, Cape Gloucester, Saipan, Peleliu, Iwo Jima, and Okinawa saw fierce fighting between Marines and the Imperial Japanese Army. Some 600,000 Americans served in the U.S. Marine Corps in World War II.
 * Headquarters Battalion, United States Marine Corps under Major General Thomas Holcome (Major General Commandant)
 * 1st Provisional Marine Brigade (in Iceland)
 * Brigade Headquarters in Alafos under Brigadier General John Marston VI
 * 1st Provisional Marine Brigade Band
 * 3rd Platoon, 1st Scout Company
 * A Company, 2nd Tank Battalion
 * 6th Marine Infantry Regiment
 * 4th Battalion, 10th Marine Artillery Regiment
 * 5th Marine Defense Battalion (-Seacoast Group)
 * C Company, 1st Engineer Battalion
 * 1st Platoon, A Company, 2nd Service Battalion Depot
 * 2 Provisional Bakery Depots (Ad Hoc units)
 * A Company, 2nd Medical Battalion
 * Provisional Chemical Platoon (Ad Hoc unit)
 * 4th Marine Infantry Regiment (2 Battalions, Marine Detachment, and Service Company) based in Naval Station Olongapo
 * North China Marines (2 Marine Guard Detachments in Peiking American Embassy and Tietsin US Legation)
 * 1st Separate Marine Anti-Aircraft Battalion at Naval Yard Cavite
 * Amphibious Tractor Detachment at Dunedin (Operation and Maintenance Support)
 * Marine Detachment at the American Embassy London

1st Marine Division

 * Divisional Headquarters at Quantico under Major General P H Torrey
 * Special Troops Battalion
 * Headquarters Company at Quantico
 * 1st Signal Company
 * 1st Scout Company (-3rd Platoon, in Iceland)
 * 1st Tank Battalion
 * 1st Marine Air Assault Battalion
 * 1st Special Weapons Battalion
 * 1st Engineer Battalion
 * 1st Marine Infantry Regiment at Parris Island
 * 5th Marine Infantry Regiment
 * 7th Marine Infantry Regiment
 * 11th Marine Artillery Regiment
 * Service Troops Regiment
 * 1st Transportation Battalion
 * 1st Service Battalion
 * 1st Medical Battalion
 * 1st Military Police Guard Company