Scuba divers in Thailand have already rescued four of the 12 boys who have been stranded, along with their coach, in a flooded cave. And they are hoping to rescue the rest in the next couple of days. But in the meantime, Elon Musk has continued working on alternative strategies divers could use if conventional diving proves too difficult for the remaining boys.

On Saturday, Musk settled on the idea of building "a tiny, kid-size submarine using the liquid oxygen transfer tube of Falcon rocket as hull." He ordered SpaceX engineers to begin building the device, saying that it could be ready by the end of the day on Saturday.



Elon Musk / SpaceX

Elon Musk / SpaceX

By the time it was finished, Thai officials had already begun their rescue operation without Musk's help, so the technology likely won't be needed. But Musk decided to press forward anyway, tweeting that "even if not useful here, perhaps it will be in a future situation."

On Sunday, he posted photos of the completed device.

"Testing for 3 more hours in LA, then it’s on a plane to Thailand," Musk tweeted late on Sunday morning, California time.

Musk also posted a video of the device being tested in a Los Angeles pool:

Testing underwater in LA pool pic.twitter.com/CDO2mtjP2D — Elon Musk (@elonmusk) July 8, 2018

Update: The tube is really narrow. Some diagrams online show one passageway narrowing to as little as 38 cm—about 15 inches—at its tightest point. We asked Musk if the cylinder would really fit through such a small space, and he responded on Twitter that the cylinder was 31 cm wide—just over a foot.

That would obviously be too narrow for many adults to squeeze into, but perhaps it's just big enough for the Thai teenagers—especially the younger ones—to get in.