Questions are being asked about the viability of nuclear vessels following the sinking of Russia's Kursk submarine despite the advantage over diesel power.

Nuclear propulsion opened the way for the development of the modern strategic use of submarines.

The USS Nautilus was launched in January 1954 to become the first nuclear-powered vessel in the US Navy.

The Russians were close behind - their first nuclear-powered boats were the November class fleet submarines built between 1958 and 1963.

The UK and France followed US and Russian moves into nuclear subs

Nuclear power gave not just extended endurance and high maximum speed. It also provided virtually unlimited power for other systems on board the boat.

As one former submarine captain put it: "On a diesel submarine one's whole life was governed by the state of the boat's batteries."

On transferring to a nuclear boat he said: "One never gave power supplies a second thought."

Nuclear propulsion opened the way for the development of that grim symbol of the Cold War - the ballistic missile submarine.

Its endurance made it very hard to find and it could lurk unseen within range of an opponent's population centres.

Surface fleets

Britain and France also operate nuclear-powered submarines. But until recently only the Russians and the Americans have sought to harness the advantages of nuclear power for their surface fleets.

Now the Americans appear to have decided that it is just too costly a form of propulsion except for their giant aircraft carriers - the centrepieces of the modern US battle-fleet.

France's Charles de Gaulle is powered by nuclear energy

The Russians have persevered with nuclear-powered warships - like the Kirov class cruisers - but are building so few new vessels today that naval experts say it is difficult to determine if they intend to continue with nuclear-powered ships.

The new French aircraft carrier - the Charles de Gaulle - is also nuclear powered and the Russians maintain a small fleet of nuclear ice-breakers for use in the frozen wastes of the Arctic.

Nuclear power is the feature that makes the modern strategic submarine what it is and it is almost impossible at the moment to see it being replaced by anything else.

The nuclear reactor is in a sense just a large boiler producing steam to run turbines.

While there is a lot of talk, especially in the US Navy, about developing all-electric vessels it seems likely that electric propulsion will be the way of the future for surface ships.

But nuclear power, with all its risks, is likely to remain the choice for the grey denizens of the deep.