SS Mission San Juan was a Type T2-SE-A2 tanker built for the United States Maritime Commission during World War II.

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.

Shortly after the cessation of hostilities, Mission San Juan was placed in the Maritime Commission Reserve Fleet at Mobile, Alabama on 9 April 1946.

Reacquired by the Navy on 28 October 1964, Mission San Juan was moved to the General Dynamics Shipyard, Quincy, Massachusetts, for conversion into a missile range instrumentation ship.

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, Portland, Oregon, and renamed SS Kopaa.