As part of the effort to expand the Marine Corps to 202,000 Marines by the end of 2011, battalions of the 9th Marines began reactivation in 2007.The 1st Battalion, 9th Marines (1/9) reactivated on April 18, 2007. The 2nd Battalion reactivated in July 2007, while the 3rd Battalion reactivated in May 2008.  Each battalion falls under existing regimental headquarters — 1/9 with the 8th Marine Regiment, 2/9 with the 6th Marine Regiment and 3/9 within 2nd Marine Regiment.

• Headquarters Company 9th Marines (HQ/9) Not activated
• 1st Battalion 9th Marines (1/9) attached to 8th Marine Regiment
• 2nd Battalion 9th Marines (2/9) attached to 6th Marine Regiment
• 3rd Battalion 9th Marines (3/9) attached to the 2nd Marine Regiment

Early years

The 9th Marines were activated at Quantico, Virginia on November 20, 1917. A month later, they deployed to Guantanamo Bay, Cuba and were attached to the 3rd Marine Brigade. That same month, they redeployed with the brigade to Galveston, Texas in case of any German operation in the Caribbean or in Mexico. After World War I, the regiment was deactivated in Philadelphia, Pennsylvania on April 25, 1919.

On December 1, 1925, the regiment was reactivated as a reserve organization whose mission was to train and maintain at a high degree of preparedness a group of “civilian” Marines.

The 3rd Battalion 9th Marines was reactivated at Camp Elliot, San Diego on February 12, 1942. In the following months, the rest of the battalions were also reactivated on January 1, 1942 when the regiment officially re-formed. They were attached to the 3rd Marine Division at Camp Pendleton on September 16, 1943. The Regiment was deactivated at Camp Pendleton on December 31, 1945.

Vietnam War

On March 8, 1965, 9th Marines came ashore at China Beach as the first conventional ground combat unit in South Vietnam.  Their mission was to defend the air base at Da Nang. The first significant contact was in April 1965. The regimental headquarters arrived in country in July of that year.

The Regiment saw action in Vietnam’s I Corps, primarily in Quang Tri and Thua Thien provinces, although a number of its earlier operations were also conducted in the southern I Corps provinces of Quang Nam, Quang Tin, and Quang Ngai. The 9th Marines served as a vital stop to the North Vietnamese penetrations across the DMZ and from along the Ho Chi Minh Trail in Cambodia.

Some of its early operations included Double Eagle, Macon and Prairie.

In April and May 1967, elements of the regiment defeated two NVA Regiments in the Hills north of Khe Sanh. In Operation Buffalo, elements of the 1st Battalion, 9th Marines made contact north of Con Thien with regimental-size NVA forces in an engagement that lasted through May, accounting for over 1300 enemy dead.

In one of the most successful operations of the war, the regiment conducted Operation Dewey Canyon in the A Shau Valley, cut by the Song Da Krong river. The 9th Regiment exacted a deadly toll on the NVA. These actions precluded another build-up and assault from Route 622 from Laos into South Vietnam as the NVA had the year before during the Tet Offensive.

Operation Dewey Canyon netted, among other weaponry, 16 artillery pieces, 73 anti-aircraft guns, hundreds of thousands of rounds of ammunition, 92 trucks, and hundreds of thousands pounds of rice.

In the words of Gen Stillwell in his report to Gen Abrams on Operation Dewey Canyon: “...this ranks with the most significant undertakings of the Vietnam conflict in the concept and results...” The 9th Marines were redeployed from Vietnam in August 1969 as part of the first redeployments.