They crossed the line at 3.30pm after almost nine hours on the water, and just one hour less than the record for the longest finishing time for a line honours winner set by Thomas Ratsey back in 1931.
Led by Pete Cumming, the former Extreme 40 champion and a past winner of the Round the Island Race in 2010, and helmed by Paul Campbell-James, the team was relived to cross the line and thrilled by their success.
Cumming said: "It wasn't the easiest race but these boats are superb - very fast even in light airs and fun to sail."
Spax Solutions, the second GC32, crossed the finish line in second place but most of the rest of the fleet were further to the east struggling with lack of wind.
At 4.30pm, there were still 100 boats west of St Catherine's with another 25 miles to go.
Retirements were coming in thick and fast, including Dame Ellen MacArthur.
There were whoops of joy coming from the Farr 45 Toe in the Water when they crossed the line ahead of Sir Ben Ainslie who they had battled with all the way round the course.
"This means everything to us," said skipper Capt Lloyd Hamilton, whose crew comprised members of the armed forces recovering from tours of duty in Afghanistan where they suffered serious injuries.
"The guys are ecstatic at beating Rebel. They don't know many of the America's Cup sailors but they know and love Sir Ben Ainslie so are thrilled."
Ainslie finished around 25 minutes later after Tonnerre De Breskens 3 and Tokoloshe II who at one point was leading the race.