Meet the Wet Mules, the Aussie dive mates at the heart of the cave rescue
In the small world of technical cave diving, known as the "Formula One of diving", the Australian group of diving mates known as the Wet Mules are highly respected for their skill, experience and spirit of adventure.
They have travelled the world, pushing the limits of exploration of the most technically challenging caves, but the Thai cave rescue will undoubtedly be the pinnacle of achievement for two of its members, Adelaide anaesthetist Richard Harris and Perth vet Craig Challen.
The philosophy of the Wet Mules — a name inspired by the southern American expression "enough money to burn a wet mule" — give an insight into the approach the men took.
They pride themselves on innovative thinking and doing whatever it takes to solve the trickiest of problems.
"As a large part of our chosen pursuit of cave diving seems to revolve around ferrying heavy objects in and out of caves, submersing ourselves in frigid waters for many hours and generally abusing our bodies in a multitude of ways, we were beginning to take on the persona of the wet mule itself!," the Wet Mules website says.
"Stubborn, strong of back and oblivious to pain: these are the qualities of the exploration cave diver!"
But within this group, Dr Harris and Dr Challen have formed a close bond, renowned as long-time dive buddies with an outstanding record of technical cave diving.
Enthusiasts like to describe technical cave diving as the Formula One of the diving world.
They have high-level skills and equipment, and a passion for exploring the undiscovered.
Given the dangers of this pursuit and the need for trust between buddies, and given that diving by its very nature is a non-conversational pursuit, it's not unusual for tight friendships to form.
New South Wales diving consultant David Strike said he was not surprised Dr Harris had asked Dr Challen to help him on the Thai mission because close personal relationships were vital in difficult dives.
"Like most divers, you tend to get used to a particular diving partner," Dr Strike said.
"Telepathy almost comes into play. You become very comfortable with a particular dive buddy, you know how they're going to react in a certain situation."
The two men have gained many years of experience together, pushing the limits of some of the most difficult caves, such as Cocklebiddy Cave in Western Australia and the Pearse River on New Zealand's South Island.
In a book entitled Dining with Divers recently published by Mr Strike and Simon Pridmore, Dr Harris wrote of the "terrible fright" he had when Dr Challen took longer than expected to return from the far reaches of Cocklebiddy Cave, considered one of the most beautiful in the world, in 2008.
"I'll give him five more minutes, I thought, and then I'll have to go," he wrote.
"Suddenly I saw a glimmer of light and there he was in front of me, empty reel in hand.
"We were high-fiving and whooping and hollering underwater."
Dr Challen told National Geographic magazine about a scary moment in their record-breaking attempt to reach the source of the Pearse River, thought to be the deepest cold-water cave, in 2011.
"I noticed going down, and I just started breathing really heavily," he said.
"It's really like a self-perpetuating thing, you know.
"You try and relax and chill, and you just can't."
It was a rare public comment for a man widely considered to be quiet, modest about his achievements and not keen on being in the spotlight.
His LinkedIn profile shows that he graduated in veterinary science from Murdoch University in 1987.
He is believed to own some veterinary practices.