Elements of the 3rd Marine Division were the first Marine units that operated in the vicintiy of Hill 55 beginning in 1965 as the Marine build up began in VietNam, Hill 55 eventually became a Command Post for various Regimental Commands beginning in 1966. On 10 September, 1965 the Commanding Officer of the 3rd Battalion, 3rd Marine Regiment LtCol. Joseph E. Muir was killed when he stepped on an explosive device while on the Hill. In 1966, this small hill was the dominant terrain feature in the 9th Marines TAOR, it was eventually cleared of mines and boody traps. Marine Engineers began construction on 29 March and Hill 55 eventually became the Command Post of the 9th Marine Regiment.

On 4 July the first leg of "Liberty Road" was completed, a distance of 3,500 meters south from Hill 55 to Route 4, and in September a battery of 15 HAWK missles were deployed to Hill 55 were it provided coverage for the Vu Gia River Valley. With the redeployment of the 3rd Division north, Hill 55 became the Command Post of the 7th Marine Regiment in April, 1967 with the 7th Marines remaining there for most of their deployment in VietNam.