CGRONTHREE consisted of High Endurance Cutters operating as command and control vessels for the Market Time patrol boats from May 1967. They provided targeting information and logistics when needed. Near the DMZ, cutters marked the 17th Parallel and kept vessels from straying into North Vietnamese waters. They also performed NGFS missions, especially in the Song Ong Doc area. They also carried doctors. All USN, USCG, VNN vessels knew they could transfer any injured personnel to the outer barrier cutter for treatment. Since the Swift boats were rough riding boats with few amenities, two crews were assigned. The off duty crew lived aboard the outer barrier cutter. Up until 1969, the outer barrier cutters were WWII-vintage ships of the 327’ Secretary, 311’ AVP, and 255’ Lake classes. Their performance was hindered by age and obsolescence. On 1 October 1969, Hamilton, a new 378’ Secretary-class, arrived on station. These cutters brought not only more speed and better NGFS ability; they also brought a flight deck.
On 22 May 1967, USCGC Barataria fired the first Coast Guard NGFS mission of the war.
Androscoggin’s medical officer once performed four hours of major surgery on a Vietnamese soldier seriously wounded by a grenade. The cutters also assisted in several amphibious landing operations along the coast.
In summer 1968, Owasco saved a Swift from sinking after it was attacked. In June 1968, Androscoggin conducted a hydrographic survey of an uncharted area.
Owasco provided illumination for an Army unit in danger of being overrun while USS New Jersey provided NGFS for the position.
In June 1969 CGRONTHREE assisted in the salvage operations for USS Frank E. Evans after she was cut in half by the Australian carrier Melbourne.
By 1970, it was time to turn operations and some ships over to the VNN. Bering Strait and Yakutat were turned over on 1 January 1971. On 21 December, Castle Rock was turned over to the VNN. In December 1971, Cook Inlet, the last Coast Guard cutter on combat patrol in Vietnam, was turned over. CGRONTHREE was disestablished on 31 January 1972.