Elon Musk has disputed reports about the usefulness of his plan to rescue the Thai boys from underground.
The SpaceX boss said he had invented a tiny submarine that could be used to carry the boys out from the cave network, without having to teach them to dive or swim.
Mr Musk's plan was reported to have been called "not practical" by Narongsak Osatanakorn, who has been co-ordinating the mission. That report came after some criticism of the plan from people who argued that the relatively large submarine would not be able to fit around the tight cave network the boys had to navigate.
“Even though their equipment is technologically sophisticated, it doesn’t fit with our mission to go in the cave,” Mr Osatanakorn told the BBC.
But Mr Musk said that he was certain the submarine would have been able to navigate the tight gaps and difficult corners inside the cave network.
"Based on extensive cave video review & discussion with several divers who know journey, SpaceX engineering is absolutely certain that mini-sub can do entire journey & demonstrate at any time," he wrote. In response to a question about a particularly difficult corner that would seem to have ruled out using the submarine, he said it was "specifically designed to pass that point".
Mr Musk also said that his submarine plan was encouraged by people working on the rescue. And he said that Mr Osatanakorn, who the BBC had described as a "rescue chief" because he is working to co-ordinate efforts, was not in a position to judge the plan.
"The former Thai provincial governor (described inaccurately as 'rescue chief') is not the subject matter expert," Mr Musk wrote. "That would be Dick Stanton, who co-led the dive rescue team."
He then shared what he said were emailed from Richard Stanton, one of the British divers who have been called in to help on the work. In those messages, Mr Stanton appeared to encourage Mr Musk to keep working on his designs.
"It is absolutely worth continuing with the development of this system in as timely a manner as feasible," one of the messages reads. "If the rain holds out it may well be used."
In response to Mr Musk's questions about whether it is definitely worth flying the submarine to Thailand, the messages from Mr Stanton reads: "We're worried about the smallest lad please keep working on the capsule details".
In the end, Mr Musk appears to have flown with the capsule to Thailand, and left it with those working on the rescue effort.
Just returned from Cave 3. Mini-sub is ready if needed. It is made of rocket parts & named Wild Boar after kids’ soccer team. Leaving here in case it may be useful in the future. Thailand is so beautiful. pic.twitter.com/EHNh8ydaTT— Elon Musk (@elonmusk) July 9, 2018
But it was not needed, and all of the Thai football team and their coach were evacuated using a method that involved two divers escorting each of them out to swim through the tunnels, despite the fact that some of the boys were not even able to swim.
Mr Musk said that the sub might still be useful. It could be used for "rescuing vulnerable patients in dangerous environments, particularly if water, toxic gas or dangerous bacteria/viruses present, as patient would remain dry and at standard air pressure entire time", he wrote on Twitter.