A video tweeted by Elon Musk shows a “tiny, kid-size submarine” being tested July 8 in a pool at Palisades Charter High School in Pacific Palisades, Calif. (Elon Musk/AP)

The world is captivated by the plight of a Thai soccer team trapped in a flooded cave — and so, too, is billionaire inventor  Elon Musk.

As rescuers began a daring extraction of the boys and their coach from the cave over the weekend, Musk said he had sent a “kid-size submarine” to the country to assist in the massive rescue effort.

“Hopefully useful,” he wrote in one tweet, noting that the device would arrive in 17 hours. “If not, perhaps it will be in a future situation.”

Hours later, Musk shared video of the narrow, bullet-shaped tube being maneuvered through an underwater obstacle course with the assistance of two divers.

The exercise, Musk noted, was an attempt to simulate moving through a narrow passage.

Eight boys have been removed from the cave by a team of Thai and international divers, but four others and the 25-year-old coach remain inside the cave, where they have been trapped for more than two weeks, according to The Washington Post’s Shibani Mahtani.

The rescued boys, whose condition remains unknown, were brought by helicopter to a hospital in Chiang Rai.

Crews are rushing to rescue the boys before the cave complex is inundated once again by seasonal rains.

Musk has been tweeting about the rescue effort for days and said he is “amazed by the bravery, resilience & tenacity of kids & diving team in Thailand.”

“Human character at its best,” he added.

He also tweeted that SpaceX and Boring Co. engineers were headed to Thailand to see whether they could assist Thai authorities. After noting that he’d been consulting with cave experts in Thailand during the weekend, the Tesla CEO began tweeting about the specifics of the “escape pod” his team was developing.

For the pod’s hull, he said, designers used a “liquid oxygen transfer tube” from SpaceX’s Falcon rocket. Testers strapped weight belts around the outside of the pod, and Musk noted the tube was light enough (about 88 pounds) to be carried across dry sections of the cave.

Musk hasn’t revealed whether his engineers have arrived on the ground in Thailand or been able to assist in the precarious rescue effort. That effort has already cost one rescuer his life.

Thai Navy Sgt. Saman Kunan, an ex-SEAL, died Friday from a lack of oxygen as he attempted to place air tanks inside the cave complex.

MORE READING: 

Flying from NYC to London in two hours is on the horizon, Boeing says

Privacy as a product: The argument for trading your personal data to get a discount on a car

Electric-scooter companies conquer with a simple strategy: Act first, answer questions later