- Class: Williamsburg - 1 presidential yacht of 1945
- Displacement: 1,805 tons
- Dimensions: 243'9" x 36' x 14'
- Machinery: 2 Winton diesels, 1,100 shp = 13.5 knots
- Complement: 81
- Builder: Bath Iron Works, Bath, ME
- Laid down: 19 Mar 1930
- Launched: 8 Dec 1930
- Completed: 15 Jan 1931
- Acquired: 24 Apr 1941
- Commissioned: 7 Oct 1941
- Decommissioned: 30 Jun 1953
- Notes: Built as the private yacht Aras for wood-pulp magnate Hugh J. Chisholm. Acquired by the U.S. Navy in 1941 for conversion to a gunboat at Brewer Drydock and Repir Co., Brooklyn NY. Commissioned as USS Williamsburg (PG-56), she was armed with two 3in guns, multiple .50cal and .30cal machine guns and depth charges. Despatched to Iceland in Dec 1941, she served for several months as flagship for the Naval Operating Base at Reykjavik. Afterwards, she served primarily on local escort duties until early 1943 when she returned to Hoboken for an overhaul. From Mar 1943 she operated as the flagship for the Commander, Fleet Operational Training Command, primarily out of Norfolk. In Jun 1945 she was slated for conversion to an amphibious force flagship (AGC) for use in the anticipated invasion of Japan, but the abrupt end of the war stopped work at the Norfolk Navy Yard. Instead, she was chosen as a replacement for the presidential yacht USS Potomac (AG-25) that had been a favorite of President Roosevelt.
On completion of her conversion and assumption of her new duties in Nov 1945, she was re-designated AGC-369. She served through the remainder of President Truman's tenure, mostly in the Chesapeake, with occasional cruises to Florida, Bermuda, Cuba, and the Virgin Islands. President Eisenhower made only one cruise in her, in May 1953 to colonial Williamsburg, before directing that she be placed out of commission. She was preserved in "special status" until being struck from the Navy list in 1962 and transferred to the National Science Foundation. She was converted to an oceanographic research vessel at the Woods Hole Oceanographic Institute and renamed Anton Bruun in honor of a noted Danish marine biologist. She made ten scientific cruises in the Indian Ocean, and then switched to the Pacific in 1965 for another eight cruises into 1968. Unfortunately she suffered extensive damage while laid up for repairs in a floating drydock that sank unexpectedly. She was offered for sale by Marad, and for a while served as a floating restaurant in New Jersey. In 1993 she was transferred to Genoa, Italy for conversion into a luxury cruise ship, but the project was not carried out, nor was a later campaign for restoration and return to the U.S. Laid up in La Spezia, she was slated for scrapping in 2016.