FIRM remained at Pier 9, Long Beach, until 10 January 1966 when she entered Fellows and Stewart Shipyard for her biannual overhaul. In March 1966 after completion of repairs and ship alterations, FIRM returned to the operating fleet for two weeks of individual ship exercises.

On 6 April 1966 FIRM commenced preparations for Mine Countermeasures Refresher Training. Extensive training through 9 May 1966 culminated in FIRM being awarded her second consecutive and very much coveted “M” for excellence In minesweeping, having demonstrated she was fully proficient In all phases of minesweeping.

After a week of upkeep FIRM participated in “Operation POPGUN” off Santa Rose Island, a two week Mine Countermeasures Exercise which further increased the ship’s MCM readiness.

Upon completion of “POPGUN” FIRM departed with Mine Division 72 for San Diego and began refresher training on 20 June 1966. After three weeks of intensive and highly successful training, FIRM returned to Long Beach having attained a peak state of readiness.

After one more MINEX, “Operation Grunion Hunt”, off Santa Rose Island, FIRM returned to Long Beach, Fellows and Stewart Shipyard, for installation of air conditioning and a second set of evaporators.

On 1 September, FIRM commenced final deployment preparations and reported ready for Seventh Fleet Operations.

On 21 September, FIRM departed Long Beach with other ships of Mine Division SEVENTY-TWO for operations with the United States Seventh Fleet. Fuel stops were made at Johnston Island and Kwajalein Atoll and voyage repairs were conducted in Guam and Subic Bay. The latter visit was required in order to replace two blades of FIRM’s port propeller, which were damaged enroute by striking a submerged object.

FIRM departed Subic Bay on 16 November and operated as a unit of Market Time, Coastal Surveillance Patrol Operations off the coast of the Republic of Vietnam during the period 19 November 1966 through 23 December 1966. On 6 December, FIRM anchored in Danang Harbor for a change of command ceremony in which LCDR L.W.FERNALD, Jr., USN relieved LCDR C.W. ROTH, USN as Commanding Officer. During these operations FIRM earned another Bronze Star to be worn on her Vietnam Service Medal which was won in 1965. She also earned the Republic of Vietnam Campaign Medal for having accumulated six months of active duty in the Vietnam combat zone.

After fifty consecutive days that included Christmas at sea, FIRM entered Subic Bay Republic of the Philippines on 28 December 1966. While enroute from the Vietnam Combat Zone to Sasebo, Japan, for an interim dry-docking, FIRM suffered a port shaft casualty which necessitated that FIRM enter Subic Bay for repairs In lieu of continuing on to Sasebo.

The year ended with FIRM inport at Subic Bay, Republic of the Philippines.