After 15 days trapped deep inside a north Thailand cave system, officials are preparing to finally rescue 12 Thai boys and their soccer coach.

Media were cleared from the area earlier in the day to make way for ambulances, military and rescue officials: the difficult rescue mission could take anywhere from four hours to four days, as expert divers guide the boys on a complex route through the caves.

Rescuers have been practising the operation for days and have a set plan: they want to extract a group of four boys first before rescuing the others.

Along with their football coach, the 12 boys were discovered stranded deep in the caves a week ago.

Prov Gov says the rescue mission is underway. They expect to have at least some boys out today, with a group of four first. #thamluangcave #thamluang #Thailand

— Liam Cochrane (@Liam_Cochrane) July 8, 2018

The mission was likely kicked into motion as concerns over monsoon rains flooding out the caves grew. One of the leaders of the rescue efforts, ex-provincial governor Narongsak Osottanakorn, told reporters today that they were “at war with water and time”.

The boys were discovered after a nine day search-and-rescue mission. It’s taken an extra week to figure out how best to extract the group from deep inside the caves.

Why Not Just Swim Out Days Ago?

The boys were stuck more than four kilometres inside the cave system, and most were weak swimmers — swimming out was always going to be a challenge.

That solution to the rescue mission was made harder by the high diving skills required to navigate the caves. At some points, the boys will have had remove their oxygen kits to squeeze through tight areas.

Expert divers have spent the past week training the boys in basic diving. But rescuers were worried that that would not be enough: on Friday, former Thai Navy SEAL Saman Kunan died from lack of air within the cave complex.

To save time, rescuers have been manually pumping water out of the caves. As monsoon season heats up, some were worried that the rainwater would flood the caves and ruin any chances of survival.

To add even more time pressure onto the situation, there were worries that the boys were running out of oxygen. Dozens of holes were drilled into the top of the cave in an attempt to give the boys some fresh air, but no long-term solution had been figured out: in some places, 400 metres of solid rock separated the surface from the boys in the cave.

A Rescue Mission That’s Captivated The World

According to CNN, schoolchildren in Mae Sai became excited when they heard that even Elon Musk had announced that he would lend a hand to the rescue mission.

Musk’s involvement (if not exactly necessary) shows exactly how widespread offers for help have been. Divers, engineers, meteorologists and cave experts travelled from all over the world to advise the mission.

In letters sent to their parents from inside the cave, the boys apologised — and asked for less homework and more fried chicken when they came out.

Yesterday, FIFA announced that they would offer the boys free tickets to the football World Cup final, if they were out in time.