The USS Bluefin was a U.S. Navy submersible that fought in the Great War. In 1915, it was fitted out to be towed by the Spray, a fishing boat purchased by the Navy and used as a decoy to attract Confederate commerce raiders. When heading out to sea or coming back to port, the Bluefin would submerge and be towed by the Spray. If attacked, the Spray's captain, CPO Patrick O'Donnell, would contact the submersible via a waterproof telephone line. The concept worked once, with the Bluefin torpedoing a surfaced submersible trying to shell the Spray with its deck gun.
However, this success brought widespread publicity making Confederate forces much more cautious with only one more successful sinking on the West Coast early in the program. The U.S. Navy decided to cancel the program and reassigned the Bluefin to other missions.