UK subs' role in the strikes

Previous cruise launch seen through HMS Trafalgar's periscope

Royal Navy submarines HMS Triumph, HMS Trafalgar and HMS Superb were involved in the first wave of attacks against Afghanistan.

At least one of the subs fired Tomahawk cruise missiles as the US and UK targeted 30 sites in the south Asian county.

The submarines belong to the Trafalgar and Swiftsure classes of "hunter-killer" subs whose main role is to seek out and destroy ships or other submarines using their five, 21-in torpedo tubes.

Although powered by a Rolls Royce pressurised water nuclear reactor, they do not carry nuclear missiles but are part of the conventionally-armed deterrent force, known as Fleet Submarines.

Capabilities

HMS Superb - Navy number S109 - is the oldest, launched in 1974. Its home base is Faslane on the Clyde.

HMS Trafalgar: May have fired some of its cruise missiles

HMS Trafalgar - S107 - was launched in 1983. HMS Triumph - S93 - is the most recent, launched in 1991. Their home port is Devonport.

Each is of a similar size, about 85 metres (280 ft) in length, and has a crew of between 115 and 130.

They are capable of 30 to 32 knots submerged.

Missiles

All Swiftsure and Trafalgar class subs are being equipped with Tomahawks but HMS Superb does not yet have them. The missiles will also be fitted to the newer Astute class of submarines when they enter service in 2005.

Strictly speaking the Royal Navy is not due to put its cruise missiles into full operational service until the end of this year, but this is not the first time they have been fired.

First to get them was HMS Splendid, which fired a test missile in November 1998 on a US military range off the Southern Californian coast.

It then fired Tomahawks in anger for the first time in the spring of 1999, against targets in Serbia and Kosovo.

The UK originally ordered 65 of the missiles, and the purchase of a further 30 was agreed in 1999 - partly to replace those HMS Splendid had fired.

Recent test

HMS Trafalgar, one of those involved on Sunday, is the latest Royal Navy sub to get the weapon.

Only last month, it fired one in the Gulf of Mexico towards a test range at the Eglin US Air Force Base in western Florida.

The UK has what is known as the "Block III" version of the Tomahawk, manufactured by Hughes - now part of Raytheon Missile Systems, based in Tucson, Arizona.

This upgrade adds a global positioning system (GPS) to the missiles guidance systems, allowing for more straightforward planning of the route the self-sufficient weapon follows to its target.

This was deemed important because in the Gulf War the relatively featureless landscape caused problems in the Tercom terrain-following guidance.

In the Trafalgar test mission, mission planning and targeting data was provided via satellite communications from the Royal Navy's operational headquarters at Northwood, north west London.

It also involved the first use of new Advanced Tomahawk Weapon Control System software, which is designed to ease joint missions involving Royal Navy and US Navy vessels.

Types of warhead

There are two non-nuclear types of Tomahawk, using different warheads.

One has what is known as a unitary warhead - a single, high-explosive charge. The other carries a cluster bomb, which dispenses a large number of smaller "bomblets".

As fitted to ships and submarines, the missile comes in a container that acts as a launch tube.

It has a solid propellant rocket booster providing 6,000 lbs of thrust for 12 seconds to power it out of the launch tube even under water.

Once airborne, panels in the side and lower part of the missile open to deploy wings and an air intake for a small turbofan engine, which takes over for the cruise portion of flight.

They have a range of between 600 and 1,000 miles.

The Trafalgar class submarines have had their problems.

Four of them were found to have faults in their reactor cooling systems of the type which controversially stranded HMS Tireless in Gibraltar last year.