Tesla CEO Elon Musk has posted photos and videos of a mini submarine that he has despatched to help rescue a group of footballers trapped in a cave in Thailand.

Musk said in a tweet Sunday evening that the pod – or “kid-size submarine” – was en route to Thailand and would arrive in about 17 hours. A video posted on Musk’s Twitter account shows a group testing the device in a Los Angeles high school swimming pool.

He said in one of the captions that the device would “hopefully” be useful and, “if not, perhaps it will be in a future situation.”

Musk explained the metal tube would be “[l]ight enough to be carried by 2 divers, small enough to get through narrow gaps” in the cave, and “extremely robust.” The device is also outfitted with oxygen ports and a nose cone to protect it from impact with rocks, according to the tech entrepreneur’s tweets.

In one of the videos of testing that Musk shared, a man is seen emerging from the roughly six-foot-long metallic cylinder.

Earlier, he had already announced that he would be sending specialist engineers to Thailand to help aid the rescue of the 12 boys and their football coach trapped in a cave.

The announcement about the submarine came after US and Thai officials confirmed on Sunday that four boys had been rescued from a flooded cave network after being escorted out by a group of Thai and international divers. Reports said eight boys in all had been rescued by Monday evening.