An American diver has given a detailed account of how the Thai cave rescue took place.
The Thai boys saved from a flooded cave endured dives in zero visibility lasting up to half an hour and in places were put in a harness and high-lined across rocky caverns, said a leader of the US dive team that was part of the operation.
Derek Anderson, a 32-year-old rescue specialist with the US Air Force based in Japan, said the dozen boys, ranging in age from 11 to 16, and their coach, who were trapped for more than two weeks, were "incredibly resilient."
"What was really important was the coach and the boys all came together and discussed staying strong, having the will to live, having the will to survive," Anderson said.
The complicated operation to bring the boys out of the cave began on Sunday, when four were extracted.
Four more were brought out on Monday, and the operation ended Tuesday with the rescue of the last four boys and their 25-year-old coach.
The group had entered the sprawling Tham Luang cave in northern Thailand to go exploring after soccer practice on June 23, but monsoon rains filled the tight passageways, blocking their escape, and pushing them deeper inside in search of a refuge.
"The cave was dry when we arrived, and within an hour and half it had already filled up by two to three feet and we were being pushed out," said Anderson.
"That was just in the very beginning of the cave and at that point we realised this problem is going to be much more complex than we thought," he said.
Falling oxygen levels, risk of sickness and the imminent prospect of more rain flooding the cave complex for months meant "the long-term survivability of the boys in the cave was becoming a less and less feasible option," Anderson said.
Divers practiced their rescue techniques in a swimming pool with local children about the same height and weight as the members of the soccer team trapped in the cave.
The aim, Anderson said, was to make each of the boys "tightly packaged" so divers could keep control of them and adjust their air supply as needed.
The process lasted hours for each boy, and involved them getting through long passageways barely bigger than an adult body.
There were about a hundred people inside the cave for each rescue operation, Anderson said, and each boy was handled by dozens of people as their perilous movement through a total of nine chambers unfolded.
In some phases they were guided by two divers. In some narrow passages they were connected to only one diver.
In caverns with air pockets they were "floated" through with the support of four rescuers.
"The world just needs to know that what was accomplished was a once in a lifetime rescue that I think has never been done before," Anderson said.
"If you lose your cool in an environment like that, there is a lot of bad repercussions," he said.