As the situation in Southeast Asia worsened, the United States began to take a more active part in the Vietnam War. Operation Jungle Drum, towards the end of 1965, landed Marines in southern Thailand. With increasing American commitments in South Vietnam, "Tom Green County" participated in Operations Piranha and Double Eagle in January and February 1966. The latter was the first large-scale amphibious landing under combat conditions since Inchon. In June 1966 the ship came under the operational and administrative command of Landing Ship Squadron 9; and, in November, the ship commenced support commitments for the Vietnam Coastal Surveillance Force, engaged in monitoring and interdicting offshore small craft traffic, TF 115. The year 1967 found the ship participating in further combat operations: Operation Beacon Torch, Operation Beaver Track, Operation Bear Chain, and Operation Kangaroo Kick. As an element of Amphibious Ready Group Bravo (TG 76.5), Tom Green County received the Meritorious Unit Commendation for these operations conducted between 18 June and 4 August 1967. During this deployment in Southeast Asia, the ship also underwent a yard overhaul at Yokosuka from 16 August to 17 November before she returned to Vietnamese waters. On 22 March 1968 "Tom Green County" arrived in the Mekong Delta region to commence a deployment as support LST for the Mobile Riverine Assault Force. On 15 April Viet Cong (VC) insurgents attacked the ship with recoilless-rifle and automatic-weapons fire, taking nine hits in quick succession. Following repairs, the ship resumed operations with Amphibious Ready Group Alpha (TG 76.4) and participated in Operation Swift Pursuit, before returning to the Mekong in December to commence resupply duties for TG 117.2—Mobile Riverine Group Bravo. While en route on 28 December, "Tom Green County" came under rocket fire from VC gunners and took seven hits on her port side.