Note: This idea became championed by Elon Musk. I wrote this before his work became public. Here is a solution for getting the Thai soccer team out of the underwater cave:
Fashion a watertight, flexible cylinder that a boy can lie in prone. It needs to be flexible so that it can be worked around tight curves in the cave. Have an oxygen supply either internally, or fed through an air tube from an external tank. The cylinder can be hooked onto the existing line that leads to the cave, and is carried along by the divers. The boy will be cocooned inside the cylinder, and will not need to do anything. He will be brought out the same way supplies are currently brought in.
"A Demon Of Our Own Design"
"The End Of Theory"
