Injured veterans and servicemen and women from across Britain are set to take part in the "hardest triathlon in the world" from London to Paris later today.
Some will use a wheelchair for the run, from Marble Arch in the capital to the south coast, while others will pedal a hand cycle with their arms from Calais to Paris, finishing at the Arc de Triomphe after a total of 300 gruelling miles.
They will also battle currents and weather as they swim the English Channel - leaving from Shakespeare Beach below the white cliffs of Dover - as they restore a sense of purpose to lives changed by traumatic injuries from improvised explosives in Afghanistan or other conditions, organisers the Help for Heroes sports recovery organisation said.
Dean Middleton, 30, a former member of the Parachute Regiment from Seaham Harbour, County Durham, suffered a serious brain injury while serving in Afghanistan in 2010 when his armoured vehicle was hit by a Taliban bomb.
He said: "Any of the guys will tell you the most frustrating thing when you're a physically active soldier is having to sit around not doing anything.
"I like to think seeing me and hearing my story gives the lads coming in some hope."
Mr Middleton suffered his injury in the Bowri desert in central Helmand and surgeons had to cut half his skull away. He had been due to attempt selection for the SAS the following year but was discharged as his problem-solving ability had been affected.
He is among 24 wounded, injured and sick military personnel and veterans named on the Help for Heroes team that will take on the Enduroman Arch to Arc challenge.
They will run 87 miles from Marble Arch to Dover, swim the English Channel, then cycle 181 miles to Arc de Triomphe.
A spokeswoman for Help for Heroes said: "Events like Arch to Arc provide our wounded heroes with a purpose and supports self-confidence as part of recovery.
"It is is billed as the hardest triathlon in the world."