Musk said the sub was en route to Thailand on Sunday. Government officials in the country confirmed last week that Musk was sending a team to help rescue efforts at Tham Luang Nang Non, a cave in northern Thailand.
Musk sent engineers from his aerospace company, SpaceX; his electric car company, Tesla; and his infrastructure and tunnel construction company, The Boring Company, according to The New York Times.
Divers rescued four boys from the Tham Luang cave on Saturday and four more on Sunday, according to Thai government officials. Four boys and their 25-year-old coach remain trapped.
The boys, who range in age from 11 to 16, and their coach decided to explore the cave system after soccer practice on June 23, according to The Associated Press. They were cut off from their exit when the cave flooded, the AP reported.
Rescue efforts were expected to resume Tuesday.