Multi-billionaire entrepreneur Elon Musk has shared photos and videos of a "kid-sized submarine" that could be used to help rescue the eight boys and their football coach still trapped in a cave in Thailand.
Four of the boys were rescued on Sunday 8 July. Thai authorities said they were in "good health" and the mission had run smoothly.
But the eight remaining boys, aged 11 to 16, and their 25-year-old coach may have to remain in the cave for another couple of days while supplies are restocked, even though they have now been trapped for over two weeks.
Musk has founded a number of American companies including SpaceX, an aerospace manufacturer and space transportation service provider.
He first tweeted about the situation in Thailand, which has been watched closely across the world since the boys and their coach were all miraculously found alive after nine days underground, on 4 July, saying he would be "happy to help if there is a way to do so."
And he has been true to his word, sending some of his top engineers to Thailand to help with the rescue, saying: "There are probably many complexities that are hard to appreciate without being there in person."
His first suggestion involved feeding a long tube through the cave system that could then be inflated with air "like a bouncy castle", allowing the boys to climb through it to safety.
And now he has tweeted details of his "Plan B" option: a man-sized metal pod, normally attached to one of SpaceX's Falcon 9 rockets, which could act as a mini submarine pushed by expert divers carrying one child at a time.
He said: "Got more great feedback from Thailand. Primary path is basically a tiny, kid-size submarine using the liquid oxygen transfer tube of Falcon rocket as hull. Light enough to be carried by two divers, small enough to get through narrow gaps. Extremely robust."
He also posted photos and videos of a team of divers testing the pod in Palisades Charter High School's swimming pool in LA, including one simulating the pod being manoeuvred through a narrow passage and another showing a man coming out of it safe and dry.
Musk added: "With some mods, this could also work as an escape pod in space."
The treacherous rescue mission, which has already claimed the life of former Thai Navy SEAL Saman Kunan who ran out of oxygen placing air tanks along the escape route, resumed on Monday morning.
The rescue team are facing a race against time to get the remaining boys out before oxygen levels in the cave get even lower and before even more rain falls during the monsoon season, which lasts until October.
Musk said: "Continue to be amazed by the bravery, resilience and tenacity of kids and diving team in Thailand. Human character at its best."