The experimental robot operates on diesel and electric power but the chief of naval operations hopes future drones can swim at much greater distances.
Adm. Jonathan Greenert told reporters he wants drones to eventually be able to swim across oceans, according to Wired.
Greenert said propulsion systems allow for 30- and 45-day missions but lack of fuel prevents those goals from being realized.
Rutgers University sent a drone on a 221-day, 4,600-mile journey across the Atlantic Ocean a few years ago.
That drone uses electricity for power and stays close to the ocean surface.
Japanese oceanographic research agency JAMSTEC sent a drone to the seafloor in 2005 and that drone traveled for nearly 200 miles.
Greenert said Penn State and Johns Hopkins researchers are also working on drones that can operate in deep seas.