An RAF plane has joined the search for four British sailors missing in the Atlantic Ocean.
The C130 Hercules aircraft took off from RAF Brize Norton at 5am on its way to Lajes in Portugal, where it will be refuelled before flying to the search area over the Atlantic, the Ministry of Defence (MoD) said. It is expected to arrive at the search area at around 2pm.
An spokesman said: "We can confirm that the UK will be providing military assistance in the search for the four British sailors.
"A C130 aircraft was deployed from RAF Brize Norton at 0500 on May 21 and has started to move towards the search area where it will join the international search and rescue effort."
The move comes after the US coastguard restarted its search for the missing men following pressure from the UK Government, the families of the crew, figures from across the world of sailing and an online petition that attracted more than 200,000 signatures.
The four men - experienced captain Andrew Bridge, 22, from Farnham in Surrey, and crew members James Male, 23, from Southampton, Steve Warren, 52, from Bridgwater, Somerset, and Paul Goslin, 56, from West Camel, Somerset - have been missing since their yacht the Cheeki Rafiki ran into difficulties about 620 miles east of Cape Cod on Thursday while returning to the UK from a regatta in Antigua.
Defence Secretary Philip Hammond said: "The RAF's contribution to the search operation for the four missing British sailors will provide additional capability and resilience to the resumed search led by US and Canadian forces.
"We all hope that the extensive resources being provided by our allies and the further support from the UK can help locate the missing yachtsmen as soon as possible."
Since resuming their search, US air crews hunting for the four British sailors have scoured almost 3,000 square miles.
The US coastguard said four vessels, two US aircraft and a Canadian military plane, were involved in searching an area about 1,000 miles east of Cape Cod in Massachusetts by air and sea.
In a statement, it said: "Air crews have searched a total of 2,878 square miles since the search has resumed. The square mileage for ship searches is still being determined.
"Weather on scene is 6ft seas with winds at less than 10 knots."
A further three ships and a US Air Force plane were on the way to assist, the coastguard added.
A search was initially launched after contact with the 40ft Cheeki Rafiki was lost in the early hours of Friday when it diverted to the Azores.
The US coastguard, Canadian aircraft and three merchant vessels searched for them throughout Friday and Saturday, with some 4,000 square miles previously scanned for the vessel's two personal-location GPS beacons until no more transmissions were received from the small devices, which have a short battery life.
On Saturday, a cargo vessel which was helping with the search spotted and photographed an overturned hull which matched the description of the Cheeki Rafiki but reported no signs of people on board or a liferaft.
The search was called off on Sunday but restarted after intense pressure from the families and supporters.
Yesterday the sailors' relatives travelled to London to meet foreign minister Hugh Robertson and go to the US embassy, and they spoke of their delight that US authorities had agreed to continue the search.
Cressida Goslin, Mr Goslin's wife, said the families had been through an "emotional rollercoaster" since Friday.
Speaking to BBC Breakfast, Mrs Goslin said hearing that the search would be resumed was "really overwhelming" and had brought "incredible" hope.
"It was wonderful, absolutely wonderful," she said.
She said her husband, an experienced sailor who has a coastal skipper certificate and a yacht master theory certificate, and the other men would be "coping well" as a team.
"We have got no reason to think they didn't make it to the lifeboat. They had advanced warning that there was a problem with the boat so we think they would have been prepared to evacuate the ship," she said.
"Social media and the petition have been fantastic because they have generated so much interest that lots of yachts have now headed to that area and family and other people have been contacting various merchant ships.
"It has been a fantastic support - everyone has joined in and there is more activity there."
The C130 Hercules, based at RAF Brize Norton, is often referred to as the workhorse of the RAF's air transport fleet.
Deputy Prime Minister Nick Clegg defended the Government's reaction to the emergency.
"Ministers were immediately despatched to speak to the search and rescue authorities in the United States so there was absolutely no doubt at all in the minds of the decision-makers on the other side of the Atlantic what this Government felt on behalf of the families who, quite rightly, are in a state of terrible anguish.
"We did, I think, what people rightly would expect of the Government," he told a caller to his LBC radio phone-in who questioned whether enough had been done.
"I am told the British search and rescue specialists feel that Americans did what one would expect of the search and rescue services in that situation across such a vast area in very difficult weather conditions."