The C130 will support two American and two Canadian aircraft alongside volunteer ships in the search for the 40ft Cheeki Rafiki.
The arrival of the RAF plane comes as the US coastguard prepared to give an update last night.
Kay Coombes, the sister of Steve Warren, one of the missing sailors, said: "We are waiting like everybody else and keep checking the internet for updates.
"The last thing we were told was what happened this morning with the coastguard and RAF plane going out. We are just glued to the TV and the phone."
The deployment of the RAF plane 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.
A Foreign and Commonwealth Office spokesman said: "We are very grateful for the extensive US-led efforts so far and welcome the decision to reopen the search.
"Every possible effort is being made to find the missing yachtsmen."
The four men, experienced captain Andrew Bridge, 22, from Farnham in Surrey, and crew members James Male, 23, from Southampton, Mr Warren, 52, from Bridgwater, Somerset, and Paul Goslin, 56, from West Camel, Somerset, went missing when Cheeki Rafiki ran into difficulties about 620 miles east of Cape Cod last 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."