By the BBC's Carole Jones at Portsmouth Harbour

The sun is setting on what has been a very memorable day - not just for Portsmouth, but for the whole of the UK.

The HMS Ark Royal has become the first naval warship to be deployed in a possible conflict with Iraq.

It was quite a spectacle watching the ship leave.

On board, 686 crew were lined up on the deck as they passed the various vantage points along the way.

There was a great roar from the crowd who had turned out in their thousands to watch the ship leave the Solent.

Crowds in their thousands saw the troops off

It was a very emotional, highly-charged departure. Many of the people on land had come from all over the UK to wave off husbands, brothers, girlfriends, boyfriends, sisters.

You could actually feel the wave of emotion coming from the shore to the ship, and vice versa.

The crew who normally would be standing to attention were jumping and waving.

It is a very exciting time for the crew, setting off an unexpected journey.

Uncertain journey

What was essentially a planned deployment could turn into a military conflict.

I think everybody on land here was very well aware of that uncertainty and anxiety that may be being felt by many members of the crew.

The crew who normally would be standing to attention were jumping and waving

The crew on board are very young; the average age is 24 and some are as young as 18.

This is their first time at sea, and there is a lot of raw emotion being felt today about these young people heading off to an uncertain future.

HMS Ark Royal is Britain's biggest battleship with a large combat capability.

It is spearheading this naval deployment of 16 warships which will meet up in the Mediterranean in two weeks' time.

They will meet up and have some intensive training exercises, and then basically they will wait for the call to see if and when they will go to the Gulf.

It was a great send-off, with hundreds of people lining the shores of Portsmouth. Brilliant blue skies, and perfect sailing conditions.

Portsmouth was upholding its very proud seafaring tradition, seeing off its sailors.