By Duncan Walker BBC News Online, on board the Ark Royal, Portsmouth

The official line may still be that the Ark Royal is leaving Britain for operations planned long ago, but on board the message is very different.

Crew members have been told they could soon be fighting a war and on the eve of their departure they said they were more than ready.

Frances Guy, 19, has been with the ship for four days

The Royal Navy's flagship will lead a task force involving 15 vessels and 3,000 marines, a deployment described by the commander of UK maritime forces, Rear Admiral David Snelson, as a "classic use of maritime power".

Troop-carrying helicopters were replacing the planes usually found on board the ships, allowing the UK to ensure there is a "ground combat capability in the Gulf region", he added.

	:	In pictures
The Ark Royal prepares for war

The crew - whose average age is 24 - were spending their final hours in port loading the boat with supplies for the mess and Naafi (Navy, Army and Air Force Institutes) shop, including 144,000 bars of chocolate and a million cigarettes.

Faced with leaving their friends and family for a possible war they were overwhelmingly upbeat and looking forward to a final Friday night blow-out in Portsmouth.

Ark Royal supplies

48,000 cans of soft drinks �50,000 of phone cards 36,000 cans of beer Free email facilities for the crew Satellite televisions and videos Two electric guitars 'for Captain Massey'

Among the senior officers there was great confidence that the men and women under their command were ready for action against Iraq, but they remained careful to avoid any suggestion they would be involved in fighting.

The Ark Royal's skipper, Captain Alan Massey, said: "The line I take with my ship's crew is that we always hope for the best but plan for the worst."

It was a message backed up by the Royal Marines' lieutenant colonel, Ben Curry, who said his troops were ready to do whatever was necessary - whether it was combat or training.

Underlining the marines' flexibility he said: "One of the most unique things is being on a ship where we can wait for months at a time and then at a moment's notice fly to where we are needed."

Leaving loved ones

Colonel Curry said debate about the merits of war was as strong among the Royal Marines as "on any high street", but the troops had signed up to do a job and were confident the right choice would be made.

Colonel Curry says the marines are ready for anything

For many of the younger crew members the prospect of war was just one of the many daunting challenges that lay ahead.

Midshipman Frances Guy, 19 had been with the Ark Royal for just four days and was getting used to the idea of leaving her loved ones behind.

She said "I'm going to miss my friends and family - my father is watching the news intently to see what I could be doing".

Sub-Lieutenant Matthew Baker, 24, said nervousness had given way to a sense of excitement for many of his colleagues.

He said "We're just training hard for any eventuality. Morale on the ship is very high, everyone knows that they are prepared for anything that may crop up."

'Credible threat'

The scale of the operation and the importance of its role is not lost on any of those involved.

Diplomacy is effective, but it is more effective when backed up by the credible threat of force Rear Admiral Snelson

It is the largest marine task force assembled by the UK in two decades and will see training in the Mediterranean followed by deployment in the Gulf and then joint operations in the Far East.

The Ark Royal will sail with around 800 people on board, but once the flotilla reaches full strength it will involve a second aircraft carrier, HMS Ocean, and around 5,000 service men and women in addition to the marines.

"Diplomacy is effective, but it is more effective when backed up by the credible threat of force," Rear Admiral Snelson said.