On 1 March 1966, Secretary of Defense McNamara ordered the reactivation of the 5th Marine Division and the division headquarters was activated at Camp Pendleton, California, in June of that year. By August, elements of the division had conducted an amphibious landing in the Republic of Vietnam and the 2nd Battalion of the 26th Marine Regiment would see combat on 1 September during Operation Allegheny. Kilo battery, 13th Marines, landed at the mouth of the Cua Viet River in May 1967. Alpha, Bravo, and Charlie 1/13 were present at the Battle of Khe Sanh in 1968. In response to the infamous 1968 Tet Offensive, President Johnson committed more troops to the war effort. On 12 February 1968, the 27th Marine Regiment was ordered to Vietnam. The 27th Marines became the first Marine regiment to fly into a combat zone. 3rd Battalion, 27th Marines participated in Operation Allen Brook and was awarded a Meritorious Unit Citation. During this operation, its members earned a Medal of Honor, 2 Navy Crosses, and several Silver and Bronze Stars. After 7 months in country, the 27th Marines was ordered back to the United States. All first tour personnel were reassigned to other units in order to complete their tours. During the Vietnam War, the 5th Marine Division comprised the 26th, 27th, 28th, and 13th Marine Regiments, and the 13th Marine Expeditionary Brigade. The division began deactivating its subordinate units on 15 October 1969. The disbandment of the division and all of its units was disbanded on 26 November.