The first USS Guinevere (SP-512) was a United States Navy patrol vessel in commission from 1917 to 1918.

USS Guinevere (SP-512)

USS Guinevere (SP-512) underway, ca. 1917.
History
United States
Namesake	Previous name retained
Builder	George Lawley & Son, Neponset, Massachusetts
Completed	1908
Acquired	10 June 1917
Commissioned	20 July 1917
Fate	Wrecked 26 January 1918
Notes	Operated as private yacht Guinevere 1908-1917
General characteristics
Type	Patrol vessel
Tonnage	499 gross register tons
Length	197 ft 6 in (60.20 m)
Beam	32 ft 6 in (9.91 m)
Draft	17 ft (5.2 m)
Propulsion	Steam engine and sails
Speed	10 kn (19 km/h; 12 mph)
Complement	75
Armament	4 × 3 in (76 mm) guns

Guinevere was built in 1908 as a private steam and sail yacht of the same name by George Lawley & Son at Neponset, Massachusetts. On 10 June 1917, the U.S. Navy acquired her from her owner, Edgar Palmer of New York City, for use as a section patrol vessel during World War I. She was commissioned as USS Guinevere (SP-512) on 20 July 1917.

Guinevere departed Coaling Station Newport at Newport, Rhode Island, on 1 August 1917 bound for St. John's, Dominion of Newfoundland; the Azores; and Brest, France. Arriving at Brest on 29 August 1917, she commenced patrols of the French coast and began escorting convoys to Quiberon, Ushant, Lorient, and St. Nazaire, France.

Guinevere ran aground and was wrecked off the French coast on 26 January 1918 with no loss of life. Her wreck was sold for scrapping to the French firm Societe Americaine de Sauvetage on 30 June 1919.