The veterans have set off from the Canary Islands.
They aim to row the 3,000 miles in under 55 days as part of the Talisker Whisky Atlantic Challenge.
The Row2Recovery group are competing against 25 other teams in the race, which will end in Antigua in the Caribbean.
The race was scheduled to start on 15 December, but stormy weather postponed the challenge.
One of the rowers, Lee Spencer, said: "We'll literally be on our own.
"We have a life raft and personal location devices and if we end up in the water swimming is not a big deal. We only have three legs between us.
"But the day-to-day chores are the things we'll struggle with."
Mr Spencer said they had been training their upper bodies to compensate for having lost lower limbs.
"We want to be an example to all people; we're just normal guys who have suffered some misfortune, but life carries on," he said.
Cayle Royce - 29, from Dartmouth. Suffered serious injuries serving in Afghanistan
Paddy Gallagher - 30, from Cambridgeshire. He was injured in Afghanistan while serving with the Irish Guards
Nigel Rogof - 56, from Hereford, who lost his leg while taking part in an RAF parachuting display
Lee Spencer - 46, from Yelverton in Devon. He lost a leg when he was struck by debris when he stopped to rescue a seriously injured motorist on the M3
Also competing are a group of four women aged 44 to 51 from Yorkshire, and 20-year-old University of Bristol aerospace engineering student Callum Gathercole, who is a solo competitor.
Crews will spend at least a month at sea, living on freeze-dried food, while raising money for charity.
Carsten Heron Olsen, race organiser, said: "This year we have 26 teams from the US, Italy, the UK, Antigua, Australia and South Africa, and there are 62 rowers in total.
"Winds look extremely favourable for the rowers for the first few days at sea, and alongside the high level of professionalism of the participants, we're anticipating a quick and competitive race and hopefully break some records.
"The race was planned to start on Tuesday, but due to strong winds going in the wrong direction we had to delay the race for a few days."
Four ex-servicemen are rowing across the Atlantic in a bid to become what is believed to be the first all-amputee team to make the trip.