Veterans and serving personnel have begun their 3,000-mile row from La Gomera in the Canary Islands, across the Atlantic, to Antigua, as part of the Talisker Whisky Atlantic Challenge.
The race will see competitors face 40-foot waves, sleep deprivation, as well as the challenges of living on a rowing boat for up to seven weeks.
In total, there are 28 teams taking part, 19 of the rowers are veterans or serving personnel.
Row 4 Victory team member Duncan Roy, a former Sapper in the Royal Engineer Regiment, told Forces News before heading off: "To be doing this with three of my best friends, representing two amazing military charities. I'm just super excited, can't wait to head out there now.
"I got a bit choked up saying goodbye to everyone knowing that it's going to be potentially up to 50 days that we're going to be at sea, away from communications."
Mr Roy's girlfriend, Apassara Wichaisri , said: "I'm a lot more emotional than I thought I was going to be.
"Duncan did it last year (rowed the Atlantic), so I thought I was going to be OK but I had a few tears this morning."
Tim Crockett, who used to be in the Royal Marine Special Boat Service, is one of the few solo rowers in the race and has been working towards the challenge for a long time.
"Ready...two years in the making," he said.
"The last three or four months have been frenetic - the last few days it's been coasting, building a little bit but happy to get started."
Mr Crockett's family will travel from their home in the USA to the finish line in Antigua to see him complete his journey. His two children, Bree and Harrison, said they are both "very proud" of him.
Former paratroopers Neil Young and Peter Ketley, known as the 'Grandads of the Atlantic', are hoping to become the oldest people to ever row across any ocean.
"Can't wait to get going. We've got a nice, slow start with winds picking up later, getting a bit choppy later on so by then we should be warmed up," Mr Young told Forces News on the start line.
Mr Ketley said: "Butterflies kicking in a little bit but that's always the case when taking part in something like this.
"But we're as ready as we can be and we're looking forward to it."
Mr Ketley's best friend, Mick Aylward, made the journey to La Gomera to see him head off. He said: "I've known Pete a long time, he told me he was doing this a year ago, and I said 'you're doing what?'.
"Followed them ever since, tried to raise their profile on social media and raise £250,000 - good luck to them!"
Video: Men of Oar - a team partly made up of serving and ex-serving personnel show us how they will be living at sea.
An all American-veteran team, Fight Oar Die, are also involved in the race.
"I'm pretty excited. It's been two years in the making but it's finally time to go," said veteran Chris Kuntz from team Fight Oar Die.