The main role of the Jet skis will be to protect nuclear submarines and warships at Devonport naval dockyard in Plymouth.

They can reach 65 mph and operate in shallower waters than other Ministry of Defence (MoD) craft.

Ships from eight countries - including America - are in Devonport at present on a visit by NATO's Mediterranean standing force.

Devonport's submarines are a possible eco target

The new "personal watercraft" put the MoD Police Marine Unit on equal terms with environmental protestors, who have been using Jet skis for a long time.

PC Andy West of the MoD Police said: "When Trident submarines come down, obviously they're nuclear and high-risk."

But the Jet skis will also be used to clamp down on leisure craft being driven dangerously in Plymouth's busy waters.

There have been two near-fatal collisions in Plymouth Sound in recent months.

Sergeant Paul Cawrse said: "If they go into swimming areas they are a danger to swimmers, and also, if they're not used properly, they're a danger to themselves."