She was launched on 18 June 1966; sponsored by Mrs. Paul V. Snow, the wife of the Deputy Counsel of the Naval Ships Systems Command.

She was reclassified a patrol gunboat on 28 March 1967 and simultaneously redesignated PG-86 and commissioned on 4 November 1967 with Lieutenant Jon Jared Gershon in command.

[4] Reaching Cam Ranh Bay on the 28th, Antelope began SEAFLOAT operations on the Cua Lon River consisting of "night harassment and interdiction gunfire; area fire preparatory to, and suppression fire during, troop sweeps; and mobile naval gunfire support for friendly forces under ambush."

Two weeks later, after she had bombarded both ends of the Rach Bien Nhan Canal, Underwater Demolition Team (UDT) swimmers went ashore and learned that her gunfire had destroyed 19 bunkers, 11 buildings, and 26 cisterns.

She returned to SEAFLOAT on 28 February, and on 2 March, while supporting sweeps ashore by troops, received about 10 rounds of small-arms fire.

There, besides serving as the command center for Coastal Division 11, she sent inspection parties on board over 350 sampans and junks between 20 March and 2 April.

[4] From 10 through 13 April, the gunboat left the rivers and entered the South China Sea to support a force of Montagnard troops landing.

Thereafter, the warship conducted gunfire support missions until 17 April, when she ended 31 consecutive days underway and headed for Cam Ranh Bay and brief upkeep.

Investigation soon revealed a 5-inch (127 mm) hole in her main deck, probably caused by "... a satchel charge catapulted from the north bank of the Cua Lon."

Five days later, while the vessel was descending the river to enter the South China Sea, opposing forces fired at least six B-40 rockets at her.

[4] After four days of upkeep at Cam Ranh Bay, the ship got underway for special operations in the Gulf of Siam and troop support in Cambodia.

At the end of May, she resumed SEA-FLOAT duties, but a failure of her number one main engine soon forced her back to Cam Ranh Bay for repairs.

After a brief stop at Subic Bay, she pushed on back to Vietnamese waters where she arrived on the last day of January and began "Market Time" duty in the Gulf of Thailand.

[4] That month she entered the Long Beach Naval Shipyard for overhaul and alterations,[4] which included the installation of two box launchers, each containing two RGM-66D Standard surface-to-surface missiles, and the Mk 87 fire control system.

During the latter half of the year, she took part in international Operation Zeus in the vicinity of Thasos island, Greece, from 21 to 29 August and NATO Exercise "Deep Furrow 73" from 20 to 30 September, before firing a missile off Crete on 1 October.

This shot scored a direct hit on a Mk 35 SEPTAR target boat and was the first successful firing in the Mediterranean of the telemetered standard surface-to-surface missile system.