Musk and engineers from his rocket company, SpaceX, built a small submarine and shipped it to Thailand to help with the rescue. The device wasn't used, and in the interview, Unsworth called it a “PR stunt” and said it wouldn't have worked to free the boys who were trapped in the flooded cave. He also said Musk “can stick his submarine somewhere where it hurts.”
Source: Los Angeles Times September 17, 2018 19:41 UTC