. By January 1966, the entire 1st Marine Regiment had completed its move to Vietnam. The first major operation in the war for a battalion of the 1st Marines was Operation Harvest Moon in December 1965.
By fall of 1967, the 1st Marines were operating permanently in the northern sector of the I Corps tactical zone. The following winter the communists launched their all-out Tet Offensive. The enemy overran Hue, the old imperial capital. Between 31 January and 2 March 1968, elements of the 1st Marines, commanded by Col. Stanley Hughes, along with other U.S. Marine and South Vietnamese units, fought to regain control of the city. Bitter street fighting and hand-to-hand combat characterized the battle. Hue was finally recaptured after the enemy suffered nearly 1,900 killed. The regiment remained deployed in South Vietnam for the next two and a half years, participating in numerous operations, both large and small. On 28 June 1971, the last members of the regiment departed Danang to return to the United States at MCB Camp Pendleton. The 1st Marines were the last marine infantry unit to depart Vietnam.