The Ministry of Defence plane sent to help search for four missing British sailors has arrived in the search area.
The C-130 Hercules aircraft left the UK on Wednesday morning and has joined the US-led search in the mid-Atlantic.
The 40ft Cheeki Rafiki, based in Southampton, was sailing back to the UK from an Antigua regatta when it started taking on water last week.
Defence Secretary Philip Hammond said he hoped the crew would be found "as soon as possible".
The yacht ran into difficulty 620 miles (1,000km) east of Cape Cod in Massachusetts and diverted to the Azores on Thursday. Contact was lost with the crew on Friday.
A search by the US Coast Guard was called off on Sunday but was resumed following an official request from the UK government.
An online petition, set up to urge the US Coastguard to resume the search, attracted more than 200,000 signatures.
The coastguard said on Wednesday that around 9,000 sq miles had been searched and there had as yet been no sightings of a life-raft, debris or a boat.
A spokesman said no decision had been made on suspending the search and it would continue into Thursday.
The RAF Hercules, deployed from RAF Brize Norton on Wednesday morning, is supporting two US and two Canadian aircraft as well as several volunteer ships in the area.
It will be based on Newfoundland for the duration of the search and scanned a section of the Atlantic ocean on its way to Canada, the Ministry of Defence said.
It is expected to conduct its first full scan of the search area at first light on Thursday.
"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," the defence secretary said.
"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."
The four missing crew members are Paul Goslin, 56, from West Camel, Somerset; Andrew Bridge, 22, from Farnham, Surrey, the yacht's skipper; Steve Warren, 52, also from Somerset; and 22-year-old James Male, from Romsey.
Three planes and six ships have already been deployed to search the area where the sailors are thought to have disappeared - approximately 1,000 miles east of Cape Cod, Massachusetts.
The World Cruising Club said more members of the yachting community were joining in the search.
Five yachts are expected to enter the search zone within the next 24 to 48 hours in addition to the single yacht already there, they said.
Admiral Richard G Gurnon, president of the Massachusetts Maritime Academy, told the BBC the search from the planes and boats was an "extremely difficult task".
"The weather is nasty, rarely is it calm and flat," he said.
"And when you have four or five people staring out windows for four hours at a time looking for what is about the size of basketballs in the ocean, it's extremely difficult. It's tiring, so this is not an easy task."
Adm Gurnon defended the coastguard's original decision to call off the operation, describing the organisation as "an extremely small outfit" faced with huge costs.
The Americans called off the operation, saying the estimated survival time past the time of distress was approximately 20 hours and that their crews had searched for 53 hours.
But the decision to resume the operation came after family members insisted they could still be alive in the yacht's 12-man life raft.
Twelve-person life raft
A raft, such as that on board the Cheeki Rafiki, is required to meet the international standard ISO 9650, which stipulates how the craft must be constructed and what it must have on board. The rafts are highly visible and buoyant and can be boarded quickly in an emergency.
- One man is known to have survived 133 days on a raft after ship was torpedoed by a U-boat in 1942, and experts have said the warmer water, the better chance of survival
- The water where the Cheeki Rafiki is understood to have encountered trouble is believed to be around 15C
Patrick Michel, skipper of The Malisi, the first private yacht to reach the search area, said he had a "gut feeling" the search would end well.
The father of James Male, one of the youngest yachtsmen, said the skipper's assurance was "absolutely excellent".
Speaking to the BBC later, Graham Male said he wanted the search to go on for "as long as it takes to cover the areas".
He said: "Emotionally for us it's all changing, it changes by the hour.
"But I think the comfort everyone is drawing from here is that James and the other crew would have done this for us, and this is actually how they would have done it if we were in that position."
Mr Male added that his son was "cool, calm and collected" and "the person you'd want to be next to in an emergency".