Boring Company CEO Elon Musk is now involved in the rescue of a group of 12 boys from Tham Luang Nang Non cave in Thailand. After the location of the young soccer team and their coach was discovered earlier this month, Musk shared ideas for the rescue mission on Twitter, later revealing that his engineers would assist with the rescue.

Musk tweeted Saturday that SpaceX engineers were close to finishing a “kid-size submarine” that might just be able to help save the stranded boys. He confirmed Sunday that the submarine was on its way to Thailand and shared videos on Twitter of divers testing out the device.

A subsequent video showed divers “simulating maneuvering through a narrow passage,” Musk tweeted Sunday.

Musk tweeted late Sunday that the sub would arrive “in about 17 hours.” There’s a chance the subs won’t be necessary; only four boys and their coach remain in the cave. Four of the trapped Thai cave boys were rescued over the weekend, and on Monday, four more were transported to the hospital.

However, as the window of opportunity for a safe extraction narrows, the mini-sub could still prove useful. Musk tweeted that the mini-sub was designed in such a way that it could safely make the trip, based on input from divers who had done it. He and his team also made an inflatable replica “so that the entire path can be tested without risk of blockage.”

Musk also said that a second sub, which is apparently 30cm shorter than the first one designed, was almost complete, meaning that more than one device would be available for the rescues.

There are only five people still trapped in the cave, including the soccer coach, but rescue operations were halted at nightfall. It could reportedly take two to four days to complete the mission, officials said, so there is a chance that Musk’s mini-sub will be there before the rescue is concluded.

Some individuals on Twitter questioned whether Musk’s assistance was all that altruistic. The billionaire businessman behind Tesla has taken some hits to his personal brand lately, and PR for his respective business ventures has been a little shaky as of late.

There’s always a possibility that some of Musk’s motivation for aiding in the Thai rescue is a veiled attempt at restoring his own public image. However, Musk said that even if the mini-sub isn’t helpful this time, it could be in “a future situation.”

Photos via Twitter (1, 2, 3, 4, 5), SXSW publicity photo