USS Seahorse (SSN-669), a Sturgeon-class attack submarine, was the second submarine and third ship of the United States Navy to be named for the seahorse.
The contract to build Seahorse was awarded to the Electric Boat Division of General Dynamics Corporation in Groton, Connecticut, on 9 March 1965 and her keel was laid down there on 13 August 1966. She was launched on 15 June 1968, sponsored by Mrs. Paul Ignatius, and commissioned on 19 September 1969 with Commander George T. Harper, Jr., in command.
Following a shakedown cruise in the Caribbean Sea and visits to Roosevelt Roads and San Juan, Puerto Rico, and Frederiksted on St. Croix in the United States Virgin Islands, Seahorse returned to her home port, Charleston, South Carolina. Through November 1970, she operated in the Atlantic Ocean and Caribbean, engaging in local operations and conducting attack submarine training.
On 30 November 1970, Seahorse got underway from Charleston on her first major deployment, in which she operated in the Atlantic and visited Bremerhaven, West Germany, before returning to Charleston on 14 February 1971. For the next four months, Seahorse conducted attack submarine training, engaged in air group operations, and made final preparations for an extended Mediterranean Sea deployment. Departing Charleston on 21 June 1971, she arrived at Rota, Spain, on 2 July 1971. She continued to operate in the Mediterranean until 4 October 1971, when she headed back to Charleston. She remained in Charleston for the next three and one-half months.
On 24 January 1972, Seahorse ran aground and was stranded for two hours while attempting to put to sea from Charleston. After breaking free, she returned to port for repairs.
On 9 February 1972, Seahorse again departed Charleston for a North Atlantic Ocean deployment, visiting Faslane, Scotland, before returning to Charleston on 11 May 1972. During the months of June, July, and August 1972, she spent four weeks at sea in the Atlantic providing services for air groups and participating in destroyer operations. In September 1972, Seahorse departed for the North Atlantic to participate in the North Atlantic Treaty Organization Exercise "Strong Express," followed by exercises with the United Kingdom and Canada in October 1972 and with the Royal Netherlands Navy in November 1972. She returned to Charleston on 5 November 1972.
Seahorse continued to operate out of Charleston into at least 1974.
Seahorse was decommissioned on 17 August 1995 and stricken from the Naval Vessel Register the same day. Her scrapping via the Nuclear-Powered Ship and Submarine Recycling Program at Puget Sound Naval Shipyard in Bremerton, Washington, began on 1 March 1995 and was completed on 30 September 1996. One of her sail planes is on public display in memorial garden at the former Sand Point Naval Air Station (now Warren G. Magnuson Park) near Seattle.