Invictus Games athlete learns breaststroke 45 minutes before winning gold medal

Mark Ormrod didn't think he'd live - let alone swim competitively - after he stepped on a landmine in Afghanistan and lost his right arm and both legs.

But the 34-year-old from the United Kingdom earned two gold medals and a silver in the pool at the Invictus Games in Sydney on Wednesday night.

"Never in a million years did I think I'd be here," Ormrod told AAP.

"The first time I went in a swimming pool post my injury, I nearly drowned and I was a pretty strong swimmer before (Afghanistan).

"That incident kept me out of the water for five years."

The former Royal Marine became the first triple amputee to survive Afghanistan, after stepping on an improvised explosive device during a routine patrol on Christmas Eve 2007.

Doctors told Ormrod to prepare for life in a wheelchair but instead, the father-of-three used the injury as a "springboard for growth and reinvention".

He took to the pool at the 2017 Invictus Games in Toronto after he figured out "how to go in a straight line".

"It was a complete experiment - I had to adapt (swimming) to my injuries and figure out what to do with my right arm, what body position to have, how many breaths to take," Ormrod said.

Another experiment for Ormrod was the 50-metre breaststroke, which he won after learning an adapted version of the swimming style just 45 minutes before the race on Wednesday night.

"I only entered it last night because there was only one entrant, so I wanted to give the crowd a race," he said.

"I had a quick little go just now in the warm-up pool and I think I figured it out."

Ormrod beat former Australian sniper team commander Garry Robinson by just 29 milliseconds in the race, which had the crowd on its feet.

Robinson said it was an honour to come "second or last" to Ormrod.

"Every time I swim now I'm thinking about my mates who died, whenever I'm hurting or tired they get me through it," Robinson told AAP.

"To have Mark beside me was very emotional."

Robinson suffered a brain injury and had to have his left leg amputated after a Blackhawk helicopter he was travelling in crashed in Afghanistan in 2010.

Three people died, including his mate Private Ben Chuck.

"After the accident I thought I'd never get back on the sporting field, I was going through serious bouts of depression and anxiety, and I thought, the old Garry's gone," Robinson said.

"But tonight, the old Garry is back."

On Thursday Ormrod is set to compete in shot put and discus, while Robinson will participate in archery.