Third Battalion Eleventh Marines was activated 1 May 1943 at Victoria, Australia as the Fifth Battalion, Eleventh Marines, First Marine Division, Fleet Marine Force. The Battalion was redesignated Third Battalion, Eleventh Marines on 7 May 1944. During World War II, Third Battalion participated in the Eastern New Guinea, New Britain, Peleliu and Okinawa campaigns. Following World War II, Third Battalion participated in the occupation of North China from September 1945 to January 1947. In December 1946, the battalion was attached to the Seventh Marines. The battalion was relocated to Camp Pendleton, California in January 1947 and was assigned to the Third Marine Brigade. The battalion was deactivated on 30 September 1947.
Third Battalion, Eleventh Marines was reactivated on 20 August 1950 at Camp Pendleton and was assigned to the First Marine Division, FMF. The battalion deployed in September 1950 to Kobe, Japan and participated in the Korean War, operating from Inchon, Seoul, the Chosin Reservoir, the East, Central, and Western Fronts. Third Battalion participated in the defense of the Korean demilitarized Zone from July 1953 to February 1955. The battalion was relocated to Camp Pendleton in February 1955.
In May 1965, Third Battalion was attached to Regimental Landing Team Seven and deployed to the Western Pacific. The battalion was assigned to the Third Marine Division in June 1965 and was later reassigned to the First Marine Division in March 1966 to October 1970, the battalion participated in the war in Vietnam, operating from Chu Lai, Da Nang, Dai Loc, and Hoi An. Third Battalion relocated to Camp Pendleton in October 1970 and was assigned to the Fifth Marine Amphibious Brigade.
The battalion was reassigned in April 1971 to the First Marine Division, FMF. Third Battalion relocated to its current home at the Marine Corps Air Ground Combat Center, Twentynine Palms, California in February 1990. The battalion participated in Operations Desert Shield and Desert Storm in Southwest Asia from August 1990 to March 1991.
From December 1992 to April 1993, the battalion was deployed as a Provisional Infantry Battalion to Mogadishu, Somalia for Operation Restore Hope. While in Somalia the battalion was instrumental in coordinating security for the city of Mogadishu with 12 other nations.
The battalion once again deployed to Southwest Asia from January 2003 to July 2003 to support the First Marine Expeditionary Force (I MEF) in Operation Iraqi Freedom. The battalion’s timely and accurate fires proved to be crucial in allowing I MEF to quickly move deep into Iraqi territory and topple the regime in 21 days of major combat operations. Immediately following the fall of Baghdad, the battalion assumed the mission of a Provisional Infantry Battalion and begun assisting in civil/military duties as well as conducting Security and Stability Operation (SASO) patrols in the capital city, securing hospitals and other vital infrastructure.
In November 2003 the battalion again received orders to deploy to Iraq, but this time as a Provisional Military Police Battalion. The battalion quickly transitioned into its new job and deployed from February 2004 to September 2004. The battalion’s motto of Semper Flexibils, Always Flexible, held true with the battalion participating in missions ranging from convoy escorts, combat patrols, humanitarian assistance, security force training, and controlling a battle space of over 40,000 square kilometers.
Today the Third Battalion, Eleventh Marines stands ready to deploy anywhere in the world.