SS Mission San Juan was a Type T2-SE-A2 tanker

Tanker (ship)

A tanker is a ship designed to transport liquids in bulk. Major types of tankship include the oil tanker, the chemical tanker, and the liquefied natural gas carrier.-Background:...

 built for the United States Maritime Commission

United States Maritime Commission

The United States Maritime Commission was an independent executive agency of the U.S. federal government that was created by the Merchant Marine Act of 1936, passed by Congress on June 29, 1936, and replaced the U.S. Shipping Board which had existed since World War I...

 during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. After the war she was acquired by the United States Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

 as USS Mission San Juan (AO-126). Later the tanker transferred to the Military Sea Transportation Service as USNS Mission San Juan (T-AO-126). She was a member of the and was named for Mission San Juan Bautista

Mission San Juan Bautista

Mission San Juan Bautista was founded on June 24, 1797 in what is now the San Juan Bautista Historic District of San Juan Bautista, California. Barracks for the soldiers, a nunnery, the Jose Castro House, and other buildings were constructed around a large grassy plaza in front of the church and...

 in San Juan Bautista, California

San Juan Bautista, California

San Juan Bautista is a city in San Benito County, California, United States. The population was 1,862 at the 2010 census, up from 1,549 at the 2000 census. The city of San Juan Bautista was named after Mission San Juan Bautista...

.

As oiler, 1943–1958

Mission San Juan was laid down on 30 July 1943 under a Maritime Commission contract by Marine Ship Corporation, Sausalito, California

Sausalito, California

Sausalito is a San Francisco Bay Area city, in Marin County, California, United States. Sausalito is south-southeast of San Rafael, at an elevation of 13 feet . The population was 7,061 as of the 2010 census. The community is situated near the northern end of the Golden Gate Bridge, and prior to...

; launched on 14 October 1943, sponsored by Mrs. Derrill D. Standifird; and delivered to the Maritime Commission on 31 January 1944 upon completion.
Chartered to Deconhill Shipping Company in February, 1944 the tanker spent the remainder of the war supplying fuel oil to American and Allied Forces overseas, during which time she was awarded the National Defense Service Medal

National Defense Service Medal

The National Defense Service Medal is a military service medal of the United States military originally commissioned by President Dwight D. Eisenhower...

.

Shortly after the cessation of hostilities, Mission San Juan was placed in the Maritime Commission Reserve Fleet at Mobile, Alabama

Mobile, Alabama

Mobile is the third most populous city in the Southern US state of Alabama and is the county seat of Mobile County. It is located on the Mobile River and the central Gulf Coast of the United States. The population within the city limits was 195,111 during the 2010 census. It is the largest...

 on 9 April 1946. Acquired by the Navy on 21 November 1947 she was retransferred to the Naval Transportation Service the same date. Designated as Mission San Juan (AO-126), she served as such until 1 October 1949 when the newly formed Military Sea Transportation Service took over the functions and ships of the Naval and Army Transportation Services. Acquired by MSTS on 1 October, she was designated USNS Mission San Juan (T-AO-126) and was placed in service with a civilian crew. During the Korean War

Korean War

The Korean War was a conventional war between South Korea, supported by the United Nations, and North Korea, supported by the People's Republic of China , with military material aid from the Soviet Union...

, she carried fuel to the forward operating bases and continued in this duty until after the war, until 12 February 1958 when she was placed out of service by MSTS, stricken from the Naval Vessel Register

Naval Vessel Register

The Naval Vessel Register is the official inventory of ships and service craft in custody of or titled by the United States Navy. It contains information on ships and service craft that make up the official inventory of the Navy from the time a vessel is authorized through its life cycle and...

 and transferred on the same date to the Maritime Administration and laid up in the Reserve Fleet at Beaumont, Texas

Beaumont, Texas

Beaumont is a city in and county seat of Jefferson County, Texas, United States, within the Beaumont–Port Arthur Metropolitan Statistical Area. The city's population was 118,296 at the 2010 census. With Port Arthur and Orange, it forms the Golden Triangle, a major industrial area on the...

.

As tracking ship, 1964–1970

Reacquired by the Navy on [28 October 1964, Mission San Juan was moved to the General Dynamics Shipyard, Quincy, Massachusetts

Quincy, Massachusetts

Quincy is a city in Norfolk County, Massachusetts, United States. Its nicknames are "City of Presidents", "City of Legends", and "Birthplace of the American Dream". As a major part of Metropolitan Boston, Quincy is a member of Boston's Inner Core Committee for the Metropolitan Area Planning Council...

, for conversion into a missile range instrumentation ship

Missile Range Instrumentation Ship

Missile Range Instrumentation Ships, Range Ships, or Tracking Ships, are ships equipped with antennas and electronics to support the launching and tracking of missiles and rockets...

. During this conversion, she was jumboized by fitting a new 72-foot section amidships and virtually rebuilt in order to accommodate the required electronic equipment. Renamed Flagstaff and designated AGM-21 on 8 April 1965, she was again renamed, on 1 September 1965, to Mercury.

Accepted by MSTS for service on 16 September 1965, she was designated as USNS Mercury (T-AGM-21) and assigned to MSTS Atlantic for duty. During the Project Gemini

Project Gemini

Project Gemini was the second human spaceflight program of NASA, the civilian space agency of the United States government. Project Gemini was conducted between projects Mercury and Apollo, with ten manned flights occurring in 1965 and 1966....

 series of orbits, she served as an important link between the astronauts and the control stations at Cape Canaveral

Kennedy Space Center

The John F. Kennedy Space Center is the NASA installation that has been the launch site for every United States human space flight since 1968. Although such flights are currently on hiatus, KSC continues to manage and operate unmanned rocket launch facilities for America's civilian space program...

. She carried out this duty until the summer of 1967 when she returned to the yard at Quincy for the installation of satellite terminals.

Upon completion of this installation on 18 September 1967, she was reassigned to MSTS, Atlantic, but shortly thereafter was reassigned to MSTS, Pacific. There she was to play an important part in the Project Apollo moon shot tests as she provided important communication links between the Apollo moon craft and earth tracking stations.

As bulk-carrier, 1970–1984

The ship was sold on 23 June 1970 to Matson Navigation Co. for conversion to a bulk-carrier at the Willamette Iron and Steel Works

Willamette Iron and Steel Works

Willamette Iron Works was a general foundry and machine business established in 1865 in Portland, Oregon, originally specializing in the manufacture of steamboat boilers and engines...

, Portland, Oregon, and renamed SS Kopaa. Sold in February 1981 to California & Hawaii Sugar Co., she was sold for scrapping at Taiwan in October 1984.