BRITISH defence experts are to test a new speedboat that doubles as a submarine for covert attacks on ports and shipping moored in harbours.
Designed to take special forces at speed to a target, then submerge to remain undetected before making a quick getaway, the craft has been commissioned for the US military.
Sources close to the project confirmed last week that the "sub-boat" would be brought to Britain next month, where it will be tested by the Defence Evaluation and Research Agency (Dera) for use by the Special Boat Squadron, the navy's special forces unit.
Capable of powerboat speeds on the surface thanks to an outboard motor developing 200hp, the engine folds away to allow it to sink to a submerged cruising depth of about 30ft. Once under water, it uses a hydro system that sucks water into tubes at the front of the vessel before blowing it out at the rear to create propulsion. Underwater speeds are slow, but the boat is quiet enough not to be heard from the surface.
The craft is crewed by two people and can carry up to four more, together with room for explosives and small arms. It is otherwise unarmed and employs "stealth" technology to make it hard to spot by radar.
The sub-boat was initially well received as a concept by American special forces but there were problems with its underwater "wake" - its trail of bubbles and disturbed water.
Now Dera, which is about to be part-privatised, is to try to solve the problems. "We believe the British have the expertise to iron out the difficulties," said one of the American project leaders last week.
The idea is not new. In the second world war the British navy used "manned torpedoes" that carried two commandos armed with limpet mines to attack enemy ships in harbours.The Americans have spent 20 years trying to perfect the concept, using a host of designs. The CIA even tried to use trained dolphins to achieve the same objective in the 1970s.
A source close to the project in the United States said: "If we can iron out the problems, and we hope that's what Dera will do, then we think this thing could end up in service on both sides of the Atlantic."
The SBS currently uses high-speed "raiders" - surface craft - to get close to the enemy before divers swim the last mile or so. However, it is hard to extract the commandos from the scene after the attack, and in many cases they simply swim to shore and attempt to escape overland.
The other tactic - bringing full-sized submarines close to the enemy - is also fraught with problems, not least because senior officers fear losing a multi-billion-pound sub on a commando raid.
Dera will start testing on computers before taking delivery of a full-sized sub-boat later this year.
