The trip by the U212A-class sub with a crew of 27 from Eckernfoerde in Germany to Rota in Spain involved the longest period that any non-nuclear vessel had ever spent under water.

The navy did not say what the previous record had been. US and Russian nuclear submarines can stay under water for longer.

Germany, which has no nuclear weapons and no nuclear-powered ships, developed the high-tech hybrid-powered submarines to replace diesel-electric vessels that need to surface more often to obtain air for the engines.

The U212A vessels have a hybrid propulsion system made up of an electric motor which is fed power from fuel cells that burn hydrogen. They must also keep air in their tanks, but need less than diesels do.

The vessel, the U 32, made the trip April 11-25 and had proved the capability of the propulsion system, a naval spokesman said in Gluecksburg, northern Germany. The U 32 is to protect the Straits of Gibraltar and Mediterranean as part of the war against terrorism.

The stealthy hybrid-powered vessels are almost noiseless and do not release any exhaust gases when under water.