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| 21st Marine Regiment | |
|---|---|
| Unit name | 21st Marine Regiment |
| Dates | 1917–1946 |
| Country | United States |
| Branch | United States Marine Corps |
| Type | Infantry |
| Size | Regiment |
| Command structure | 5th Marine Division |
21st Marine Regiment The 21st Marine Regiment was an infantry regiment of the United States Marine Corps activated during periods of major mobilization in the 20th century. The regiment served in expeditionary contexts linked to World War I, World War II, and Pacific campaigns, operating alongside formations such as the 5th Marine Division, 2nd Marine Division, and elements of the United States Army and United States Navy. Its personnel included officers trained at Marine Corps Schools, Quantico, veterans from Brevard County, Florida recruitment drives, and sailors attached for amphibious operations coordinated with Naval Combat Forces.
The regiment's history intersects with American expeditionary deployments in the Atlantic Ocean, Pacific Ocean, and island campaigns spanning the interwar period and global conflicts. During its activations the regiment worked in joint operations with units from the United States Army Air Forces, Royal Navy, Royal Australian Navy, and allied forces in the Southwest Pacific Area and Central Pacific Area. Engagements and organizational changes reflected policies from the War Department and directives issued by commanders including figures associated with Fleet Admiral Chester W. Nimitz and General Douglas MacArthur.
Constituted amid mobilization after the United States entry into World War I following the Zimmermann Telegram and Lusitania controversies, the regiment organized under the administrative control of the Department of the East and training oversight from Plattsburgh Barracks and Marine Barracks, Quantico. Elements drilled with artillery detachments trained at Fort Sill, coordinated with Army Service Corps logistics, and prepared for deployment to European theaters synchronized with convoys from Newport News, Philadelphia Navy Yard, and Hoboken. While the regiment did not complete mass overseas combat deployment like the 2nd Division (United States) Marines at the Battle of Belleau Wood, its formation contributed personnel to expeditionary battalions serving in support roles during the closing months of the war.
Following World War I demobilization directives from the National Defense Act of 1920 and budget cuts under the Washington Naval Treaty era constraints, the regiment experienced reductions and reassignments involving the Fleet Marine Force concept and doctrinal debates at Marine Corps Schools. Reorganizing during the 1920s and 1930s, the unit exchanged officers with units posted to Guantanamo Bay Naval Base, Quantico, and San Diego. The interwar years saw emphasis on amphibious doctrine influenced by publications from General John A. Lejeune and collaboration with United States Fleet Training Command and Chief of Naval Operations staff planners.
Reactivated for World War II under the auspices of expansions directed by President Franklin D. Roosevelt and the War Department, the regiment joined amphibious task forces in the Pacific War against Empire of Japan forces. Training involved assault exercises with Landing Craft, Vehicle, Personnel and coordination with Task Force 58 and III Amphibious Corps. The regiment participated in island-hopping campaigns that intersected with operations on islands associated with the Gilbert and Marshall Islands campaign, Marianas campaign, and operations adjunct to the Battle of Iwo Jima and Battle of Okinawa, while supporting naval gunfire from Battleship Division 7 and carrier air strikes by Carrier Air Groups.
The regiment conformed to tables of organization for Marine infantry regiments, typically comprising three infantry battalions, a regimental headquarters, and attached support elements including weapons companies, mortar platoons, reconnaissance detachments, and medical sections drawn from Naval Hospital Corps personnel. Command relationships placed the regiment under divisional commands such as the 5th Marine Division or temporary control of III Amphibious Corps for specific operations. Logistics depended on the Service Command, Pacific and supply from bases like Pearl Harbor, Henderson Field, and advanced bases supported by Seabees.
Units and individuals within the regiment earned campaign credits associated with the Pacific Campaign, 1941–45 and received unit citations and individual awards including the Presidential Unit Citation, Navy Unit Commendation, Silver Star, and Bronze Star Medal for actions in United States-designated campaigns. Campaign streamers mirrored major operations recognized by the United States Navy and the Department of the Navy with theater credits recorded in Marine Corps unit histories alongside those of sister regiments such as the 1st Marine Regiment and 27th Marine Regiment.
Officers and enlisted leaders who served with the regiment included those later prominent in Marine Corps leadership, some of whom trained at Naval War College or served on staffs of commanders like Admiral Raymond A. Spruance and General Holland M. Smith. Selected company commanders, warrant officers, and noncommissioned officers who distinguished themselves during amphibious assaults received individual decorations and later assignments to posts at Quantico, Camp Lejeune, and Marine Corps Base Camp Pendleton.
Category:Infantry regiments of the United States Marine Corps Category:United States Marine Corps in World War II