“With more than 70pc of the planet's surface covered by water, the oceans remain one of the world's great mysteries and untapped resources,” said Commander Peter Pipkin, the Royal Navy's fleet robotics officer.

"It's predicted that in 50 years' time there will be more competition between nations to live and work at sea or under it. With this in mind that the Royal Navy is looking at its future role, and how it will be best equipped to protect Britain's interests around the globe.”

One concept envisioned is manned “mothership” submarine with a whale shark mouth and the body of manta ray, which would be faster than anything currently in service.