Elon Musk is testing equipment designed to help rescue the remaining members of a Thai youth soccer team who are trapped in a cave, the Tesla CEO tweeted on Sunday.

Hours after four boys were confirmed to have been rescued from the cave, Musk tweeted a video of a small submarine-like vessel being tested in a swimming pool.

Earlier this week, Musk offered engineers from two of his other companies – SpaceX and The Boring Company – to assist the Thai government. The video shows three people in scuba gear pushing and pulling the tube across a pool.

Sam Teller, the spokesperson for the Boring Company, said four company engineers were "offering support in any way the government deems useful."

Here's another look of the vessel:

Musk first tweeted about the boys trapped in the cave on July 4 after somebody asked him if he would assist. He wrote that he would be "happy to help if there was a way to do so."

Musk then started brainstorming ideas to help via tweet. On Friday, he tweeted that "SpaceX & Boring Co engineers heading to Thailand tomorrow to see if we can be helpful to govt."

In one tweet, he suggested that a tube or series of tubes be sent through the cave network and inflated, creating a tunnel for the team to travel through without needing to scuba dive.

On Saturday, Musk tweeted that he was interested in designing "a tiny, kid-sized submarine" that would be "light enough to be carried by 2 divers, small enough to get through narrow gaps."

In later tweets, Musk said that the submarine he is working on has four handles in the front and four in the rear, along with four air tank connections. He also confirmed that the device could manoeuvre through the most narrow passages.

Eight members of the soccer team, ages 11 to 16, and their 25-year-old coach remain trapped in the cave. Officials said the rescue could take four days to complete. The team has been trapped in the cave for two weeks.

This article was originally published by Business Insider.

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