Hippocampus, an 23-ton motor boat, was built at New York in 1912-13. She was leased by the Navy in June 1917 and commissioned as USS Hippocampus (SP-654). Through the rest of World War I, she was used as a harbor patrol craft at Rockland, Maine, and in Penobscot Bay. Hippocampus was decommissioned in November 1918 and returned to her owner in April 1919.