Last year, a group of eight Royal Marines broke the Guinness world record for speed-marching. This is how they did it.

Filmmaker Chris Terrill, who, as a civilian, has undergone the 32-week Royal Marines Commando training course and graduated with an honorary Green Beret, filmed the group’s preparation and attempt. The group of active and former commandos completed the speed march in four hours, 16 minutes and 43 seconds, shaving two minutes out of the previous world record.

This was their third go at the Guinness world record. In 2012, they came close to success, but overshot the time by two minutes. The next year, in 2013, they broke the record but were disqualified because they didn’t finish as a group — one of their numbers, Dave Perret, succumbed to the rigours of the exertion and collapsed, avoiding death only because of the prompt response of his teammates and the paramedics.

“That moment when he collapsed, was a difficult one for me,” said Major Scotty Mills, the officer in charge of the group. “Because he pushed himself beyond the limit of what was humanly possible for him. It was down to me to decide what to do. I’d the paramedics with me and the consulting doctor … but I took one look at Dave. It was a very easy decision for me … He’s one of my brothers. I’ve served in Iraq with Dave, and there’s no way I’d his life in unnecessary risk.”