Elon Musk's sub offer was a 'stunt': diver

Elon Musk's sent a "tiny kid-sized submarine" to help rescue the Thai boys trapped in a cave

A British diver who helped with the Thai cave rescue has dismissed billionaire Elon Musk's offer of a miniature submarine as a publicity "stunt".

"He can stick his submarine where it hurts," Vern Unsworth told CNN on Saturday.

"It just had absolutely no chance of working. He had no conception of what the cave passage was like. The submarine was about five foot six [inches] long, rigid, so it wouldn't have gone 'round corners or 'round any obstacles. It wouldn't have made the first fifty metres into the cave... just a PR stunt."

Unsworth was part of an international team of cave-diving experts who rescued the group of 12 teenage boys and their coach last week. The "Wild Boars" football team had been stuck in the cave since June 23.

The rescue involved scuba diving through narrow passageways that remained totally submerged in water.

In the midst of the operation, Musk tweeted on Tuesday, apparently from Thailand: "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."

When asked about Musk being in the cave, Unsworth shrugged and said: "and [he] was asked to leave very quickly, as he should have been".

The group are recovering in hospital in Chiang Rai and are expected to be discharged this week.