The United States Navy was the aquatic military force of the United States of America.
According to a news report that Anji, Fitz and the Eighth Doctor saw, the USS Delaware was a US Navy vessel that was once attacked 40 miles off the Libyan coast by EZ jet bombers. (PROSE: Trading Futures)
The USS Cyclops was a US Navy vessel that mysteriously sank in the Bermuda Triangle in 1918. The Tenth Doctor and Heather McCrimmon discovered that it had been attacked by an Octopod whose spacecraft had crashed in the Triangle previously. The Doctor told Heather that he could not save the ship as it was part of history. (COMIC: Cyclops)