Former Navy diver Ashley Semmens has set his sights on becoming the first person to swim the English Channel — in a peculiar backwards manner.

To achieve the record, the former Chief Petty Officer will need to swim on his back for more than 15 hours, not in a traditional backstroke, but dolphin kicking while facing the sky, with minimal use of his arms.

He said preparing for the 34.2-kilometre swim was as much mental as physical.

"The kicking is effectively how I would work in my previous profession," he said.

"But as a clearance diver there is a mental resilience that I will be taking into the swim.

Mr Semmens said the beauty of the Sunshine Coast made training easy.

"The epic coastline provides everything I need, from long slow swims on the calm days to the fun of doing battle with the surf when the seas get rough," he said.

Challenge for a cause

The channel swim is set for June 2025 and aims to raise money for the Navy Clearance Divers Trust.

The trust is close to Semmens' heart as a retired clearance diver who was medically discharged from the Navy in 2022 after 20 years.

Mr Semmens said he developed post-traumatic stress disorder (PTSD) after his exit.

"In July of 2012 I was in a Bushmaster vehicle early in the morning when 500 metres down the road, it initiated an improvised explosive device, I was lucky to survive," he said.

"In the six months I served in the Middle East, I actually also lost a colleague in an IED attack, I was targeted by a sniper, and my son was born back in Australia, so I missed the birth.

He said living through being blown up gave him a rare opportunity.

"I'm using that opportunity to serve those that I can no longer stand on the front lines with," he said.

"I hid my mental challenges for 10 years because I was worried I was going to lose my job.

"It got to the point where I was more worried about losing my life, I knew I needed to get out and get the help that I needed."

Reaching breaking point

Mr Semmens said he loved his job but it took its toll physically and mentally.

"I saw the world and had incredible experiences that I would never change," he said.

"But the breaking point for me was following the evacuation of Afghanistan.

"I had retrained as an interrogator, and I had done everything in the diving world I could do.

"During this deployment I was promoted as a Chief Petty Officer, where I was forced to move to Sydney away from my family.

"And that's when everything came crashing down with all the events of the past 20 years compounded."

Mr Semmens said he was self-medicating with alcohol, which led to a breaking point.

"I wasn't well enough to work, and I was quickly put on the sidelines," he said.

"I moved back to Brisbane and started the process of getting better, which is ongoing to this day."

In elite class

A former elite swimmer growing up in South Australia, he swam at the 2003 Australian Championships going stroke for stroke against Grant Hackett in the 800-metre freestyle.

He said training for the swim had given him something to look forward to each day.

"I grew up in and around the water and I would say it has fostered my recovery," he said

"Since retiring I have been searching for a reason to put the wetsuit back on.

"It made sense to do that whilst raising funds and awareness for ex-service people".

Coach and mentor Scott Berringen, who taught Mr Semmens, said he was an elite swimmer.

"I am proud of Ash's achievements to this point but particularly his vision and how he has been able to turn his circumstances into the motivation to help other people who have been through similar things," Mr Berringen said.

"The fact he has been able to turn his situation around is admirable.

"I urge everyone to get behind him, it's not a personal pursuit, it's based on helping other people."