Washoe County departed Norfolk, Virginia, on 27 August 1956 and headed for the Mediterranean and her first tour with the United States Sixth Fleet.

On 10 June 1958, she began supply runs to Seal Beach, Port Hueneme, and San Nicolas Island, California.

Washoe County returned to San Diego on 26 June 1958 for a month's rest before sailing for Pearl Harbor, Hawaii, on 23 July 1958.

During the early months of 1959, Washoe County was at San Diego preparing for an upcoming Western Pacific (WestPac) deployment.

She returned to San Diego on 26 November 1959 and conducted local operations in waters off the California coast through the end of the year.

She spent September and October 1960 carrying United States Marine Corps troops and vehicles with stops in Naha and Buckner Bay, Okinawa, and Numazu, Japan.

On 17 February 1962, Washoe County began her participation in the large-scale Southeast Asia Treaty Organization (SEATO) Exercise Tulungan in the Philippine area which lasted through 20 April 1962.

She then devoted the remainder of 1962 to visiting the ports of Keelung, Taiwan; Subic Bay, the Philippines; Hong Kong; and Beppu and Kyūshū, Japan.

During August and September 1964, Washoe County conducted special operations in the South China Sea off the coast of Vietnam.

She served in a pioneering role as an advance base providing gunfire support, arms, ammunition, rations, and water to assault boat groups.

On 18 June 1966, the ship sailed for Okinawa to reload supplies, then made a visit to Hong Kong before resuming her duties as a cargo carrier along the Vietnamese coast.

After a week of training with the Republic of Korea Navy, Washoe County returned to Iwakuni, Japan, and embarked Marines and cargo.

She spent the month of January engaged in shuttle runs carrying cargo and personnel along the South Vietnamese coast and Okinawa and then enjoyed a rest and recreation visit to Hong Kong.

She then returned to Vietnam, but further problems with the port shaft developed, necessitating more extensive repairs at Subic Bay which lasted until 29 April 1968.

En route on 20 June 1968, Washoe County embarked two injured personnel from the American freighter SS John C. after that ship had run aground on the north reef of the Paracel Islands.

She also dispensed fuel, food, water, and ammunition to 134 patrol boats and fired 42 naval gunfire support missions.

Washoe County began 1969 preparing for the cyclical yard overhaul period which commenced on 19 January 1969 and continued through 10 April 1969.

On 12 June 1969, Washoe County got underway for the first deployment of the year as a support ship for Operation Seafloat/Tran Hung Dao III in the Ca Mau Peninsula of South Vietnam.

Seafloat was a floating advanced tactical support base primarily for psychological warfare missions conducted in the Cua Lon River at the southernmost tip of South Vietnam.

Departing Japan on 28 October 1969, Washoe County participated in Operation Keystone Cardinal, a major troop redeployment lift from Vietnam.

During November, Washoe County steamed more than 7,000 nautical miles (12,964 kilometers) bringing troops and equipment from Vietnam to Okinawa before returning to Yokosuka on 3 December 1969 for annual inspections and the Christmas holiday season.

On 12 August 1970, Washoe County arrived at Osaka, Japan, to enjoy four days at the World's Fair, Expo 70.

After stopping at Chu Lai, Vietnam, and Subic Bay, the Philippines, to load cargo on board, Washoe County headed for the California coast, via Pearl Harbor, arriving at San Diego on 10 November 1970.

At that time, she was transferred to the Maritime Administration for layup in the National Defense Reserve Fleet at Suisun Bay, Benicia, California.