Shape of things to comePentagon interested in submersible aircraft

Published 24 October 2008

DARPA asks for proposals for a submersible airplane; the agency admits that this has never been done before, and that many of the design requirements of airplanes contradict the design requirements of submarines; still, the agency says that we may solve the contradiction if we were to think not of a flying submarine, but of a submersible aircraft

Here is an interesting idea which brings James Bond to mind: The United States wants to develop a submersible aircraft that can fly hundreds of nautical miles, weather rough seas, and then go under water to insert commandos on a hostile shore. The Defense Advanced Research Projects Agency (DARPA) admits it has never been done before “because the design requirements for a submersible and an aircraft are diametrically opposed.” Still, in a request for proposals (RFPs) earlier this month the agency said it was looking for “radical new technologies that can provide a game-changing Department of Defense capability for inserting small teams clandestinely, along coastal locations.”

DARPA is famous as the originator of many of the Pentagon’s most revolutionary innovations, from the Internet to the stealth technologies to ray guns. Its proposal asks for feasibility studies and experiments to prove concepts for a submersible aircraft with the speed and range of an aircraft, the loiter capabilities of a boat and the stealth of a submarine.

The proposed craft should be able to fly commandos 1,000 nautical miles (1,850 kilometers, 1,150 miles) into a theater of operations, fly close to the sea surface for another 100 nautical miles, and then travel underwater for the last twelve nautical miles. It should be able to do all that in eight hours.

The craft should then be capable of loitering for three days in seas with up to four-meter (13-foot) waves. This is just the beginning. The craft should have enough fuel left over to extract the commandos and fly to a rendezvous point 100 nautical miles away.

Given the list of diverging requirements and design considerations, the difficulties involved in developing a submersible airplane are clear,” DARPA said. Indeed. Aircraft are designed to be light and buoyant. Submarines, on the other hand, need weight to remain submerged, as well as thick skins that can sustain the pressure of being underwater. Differences in densities of water and air, and in velocities and loading requirements, all make for aircraft and submarine design requirements that work against each other.

The DARPA proposal said previous attempts failed because they focused on making a submarine fly. “The design concept being evaluated here is for a submersible aircraft, not a flying submarine,” it said. “While it is hard to envision a propulsion system that could ever get a craft with the weight of a submarine airborne, it may be possible to submerge an extremely buoyant platform like an aircraft if the operating depths can be minimized.”