USS Thor was a cable repair ship that supported Project Caesar, the unclassified name for installation of the Sound Surveillance System (SOSUS).

Originally the Artemis-class attack cargo ship Vanadis (AKA-49) which was briefly in commission from 9 July 1945 to 27 March 1946, it was converted in 1955 after nine years in the reserve fleet.

Vanadis (AKA-49) was laid down on 18 April 1945 under a Maritime Commission contract (MC hull 1910) at Providence, Rhode Island, by the Walsh-Kaiser Co., Inc. and launched on 8 June 1945 sponsored by Mrs. J. Henry Gill.

On 30 June, she entered the Bethlehem Steel Co.'s yard at Baltimore, Maryland, for conversion to a cable repair ship.

[2] The ship was principally used to transport, deploy, retrieve and repair cables and to conduct acoustic, hydrographic, and bathymetric surveys under Project Caesar.

[1] Following an overhaul at Boston in the spring of 1962, Thor deployed to the Pacific once more for cable repair operations in the northern reaches of that ocean.

In October, she returned to the eastern side of the Isthmus of Panama and busied herself with cable repair duties and oceanographic projects in the Caribbean.

She conducted special operations in the vicinity of Midway Island and returned to Hawaii on 16 June for several days before departing Pearl Harbor on the 24th for the Marianas.

In August 1969, after seven months of operations along the east coast, she headed, via the Panama Canal and San Diego, to Pearl Harbor.

Through November, she conducted operations near Midway Island and then returned to the Atlantic via Pearl Harbor, Long Beach, and the Panama Canal.

In mid-February 1971, the cable repair ship resumed normal operations until late June when she deployed to the Pacific once more.

She completed those repairs late in the month and, after visits to Esquimalt, British Columbia, and San Diego, transited the canal on 20 September and arrived in Portsmouth, New Hampshire, eight days later.

She completed her assignment at the end of the month and, after another visit to Holy Loch during the first week in March, headed back to the United States.

On 17 March, she returned to the Portsmouth Naval Shipyard to begin preparations for decommissioning incident to her transfer to the Military Sealift Command.