A British diver involved in the Thai cave rescue has criticised Elon Musk's miniature submarine as just a PR stunt, saying he can "stick his submarine where it hurts".
Diver Vern Unsworth told CNN Mr Musk's submarine had "no chance of working".
The Tesla billionaire made headlines around the world when he announced he would build a child-sized submarine to help rescue the 13 members of the Wild Boars soccer team trapped in Thailand's Tham Luang cave.
He dropped off the device in person, just days later, after the first few boys had already been freed from the cave.
Mr Unsworth said Mr Musk's efforts to help rescue the boys was just a "PR stunt".
"It just had absolutely no chance of working," Mr Unsworth told CNN.
"He had no conception of what the cave passage was like.
"The submarine I believe was about 5 foot, 6 [inches] long, rigid, so it wouldn't have gone round corners or any obstacles.
"It wouldn't have made the first 50 metres into the cave from the dive start point."
After his device and efforts were criticised on social media Mr Musk tweeted a reply.
"This reaction has shaken my opinion of many people," he said.
"We were asked to create a backup option & worked hard to do so. Checked with dive team many times to confirm it was worthwhile. Now it's there for anyone who needs it in future. Something's messed up if this is not a good thing."
Mr Musk also released details of an email exchange with one of the other British divers involved in the rescue operation, Richard Stanton, in which the diver told Mr Musk that if the rain held out his submarine "may well be used".
The tech entrepreneur has also questioned the role of Chiang Rai provincial Governor Narongsak Osatanakorn as the rescue mission's leader, after he declared Mr Musk's submarine not practical for the rescue mission.
The 12 boys and their coach are now free and recovering from their ordeal in hospital.
