https://thenextweb.com/science/2018/07/09/watch-elon-musks-rescue-submarine-for-the-thai-soccer-boys-team-in-testing/

The world has been watching closely as a mission to rescue a soccer team of young boys in Thailand from a flooded cave is underway. Last week, Tesla and SpaceX CEO Elon Musk offered his support by promising to have a “kid-size submarine” built – and he came through with the help of engineers in his employ.

The idea is to turn a “liquid oxygen transfer tube” from a SpaceX Falcon rocket into a submarine that would be light enough to navigate through narrow gaps in the complex cave system, and be carried by two divers. The submarine can fit a person inside with their arms crossed, so it can be used to safely extract the soccer team one at a time.