Nine months of rigorous training to become a Royal Marine and it all comes down to the four Commando tests: the Endurance Course, a nile-mile speed march, the Tarzan Assault Course and the 30 Miler.
A gruelling week begins with the six-mile Endurance Course and four-mile run back to the Commando Training Centre Royal Marines (CTCRM) on the Saturday, followed by a day's rest and the nine-mile speed march on Monday, both to be completed carrying 21lbs of equipment and a 10lb rifle.
Next up on Tuesday morning is the Tarzan Assault Course - a high obstacle confidence course that must be finished in 13 minutes, also carrying 21lbs and a rifle - before the dreaded 30 Miler on day four, starting one hour before dawn at the north end of Dartmoor and culminating near Plymouth.
It's the 30 Miler that many regard as the toughest test. Thirty miles of speed marching on treacherous terrain, whatever the weather, to be completed in eight hours and while carrying 40lbs of equipment, including satellite phones, medical packs, collapsible stretchers and rifles. It's no wonder it's been described as "one of the hardest tests undertaken of any military force in the world".
Recruits are provided with all the tools they need to pass the 30 Miler, but according to former Royal Marine Mark Time, the speed march across Dartmoor is as much about being mentally prepared as being physically prepared.
"The 30 Miler is the culmination of a graduated physical training regime designed by some of the country's leading physical trainers," said Time in 2015. "With a body broken by months of unrelenting military training, these tests are passed with mental fortitude, grit and determination as much as with physical prowess."
This 'State of Mind' is ingrained in recruits by the time they tackle the 30 Miler and for Recruit Ben Davies, it was the ethos of brotherhood that enabled him to push his physical and mental capacity as he marched towards Plymouth.
Recruit Davies immediately bonded with a fellow recruit during the Royal Marines training and claims they encouraged each other - and those around them - throughout the 30 miles.
"We just kept each other going - it was nice having someone you could rely on the whole way through," he said. "He's at the same physical and mental level as me, so we started together and finished together.
"There was a couple of times where lads at the front would go to the back and help those who were lagging behind. When you spend nine months with someone, you want them to pass with you.”
But not everyone can be helped. Recruit Davies recalled the first and second checkpoints - of which there are six - as being the hardest part of the 30 Miler because of the pace they set and the boggy terrain, which was too much for one injured recruit, who had to be pulled out at the 17th mile.
"The weather was absolutely perfect. Nice and frosty in the morning and when the sun came up it was cool," he added, "but the underfoot was horrendous. The idea is to get as much time in the bag as you can at the beginning so that you can walk nearer to the end. On every downhill slope and every flat piece of ground we were running.
"But one of the lads was stopped at the 17th mile because he was injured. He couldn't keep up at the first couple of checkpoints which meant we were getting slower and didn't have as much time at the end. We came in at seven hours and 50 minutes, but it could have been seven hours and 20 minutes."
Exhaustion sets in at the halfway stage. With 15 miles covered, reality strikes for recruits that they have to do it all over again - and it's not going to get any easier. Royal Marines Reservist Jack Ardagh, who earned his Green Beret in 2017, hit a brick wall at the third checkpoint but pushed through the pain barrier.
"At halfway I felt I'd achieved something - we've done 15 miles - but then three miles later I was exhausted," said Jack. "My brain was saying I haven't really achieved anything because I have 13 miles to go. I can't do this. I had to push myself and go into a different mode then. It's mind over body. Mind over pain."
Alongside Jack was fellow Reservist Toby Webb, who also had to dig deep as they marched past checkpoint four and descended down the moor: "The roads and the downhill running was the hardest part for me. At the end when you're really pushing to get that last bit of time in it was definitely mentally: 'Right, grit your teeth now.'"
Recruit Davies, on the other hand, said it was a case of following the instructions his Physical Training Instructor (PTI) gave to him and just focusing on reaching one checkpoint at a time.
"As long as you're eating and drinking, it's just a lot of time on your feet," he said. "When you break it down into the six sections, as long as you get to your next checkpoint and do everything you've been told, you'll be OK."
The prize of a Green Beret - not to mention the fear of failure - ultimately spurred Recruit Davies over the moor: "At the end of the 30 Miler you're getting your Green Beret and that's what all the lads have on their mind. You don't want to go through it again."
And when the finish line was in sight, Recruit Davies can remember a feeling of relief as he looked to his companion and said: "This is it. Our Green Berets are over that bridge."
Mark Time describes the Royal Marines as an "elite organisation", and for Recruit Davies, completing the 30 Miler to be given his Green Beret and then passing out earned him entry into the "best boy's club in the world".
"I feel very privileged to have accomplished something not many people have," he concluded. "I'm in the biggest and best boy's club in the world. I feel humbled and proud."