HONG KONG - “The cast definitely all felt fear at various times,” says director Ron Howard, who’s revealing how he shot the rescue of a Thai boys’ football team from a flooded cave, for his latest film. Thirteen Lives tells the story of the perilous real-life rescue of the boys and their coach, trapped deep inside the Tham Luang cave network after monsoon rains came early in 2018. “A couple of the actors admitted later they had some trying moments, but nobody had to leave the tank and breathe into a brown paper bag,” the double Oscar-winner tells the BBC. The film stars Viggo Mortensen, Colin Farrell, Joel Edgerton, Tom Bateman and Paul Gleeson as the divers, who guided the footballers along underwater spaces so narrow they could barely squeeze through. The Thai caves are made of limestone, which accumulates water until it’s saturated and then floods - in this case with calamitous results. The actors had to replicate the conditions endured by the real-life divers. Bateman plays Chris Jewell, a British computer software consultant and expert cave diver, who was part of the rescue mission. The two kept in touch on set by text, so the actor could ask him about the role. “Every single day was a challenge for me,” Bateman says, adding he had scuba dived before, but had never done cave diving. “I didn’t quite realise how it made you feel... I suffer greatly from claustrophobia and I did meditate a lot,” he says, on how he coped.

The actor is able to smile about it now, but he describes getting stuck underwater for about seven minutes while guiding a female diver, who played one of the boys, through a narrow passage.

The boys were heavily sedated for the rescue. Had they been awake, the likelihood is they would have panicked and injured themselves, and the diver.

“I had this amazing stunt double, she just had to lie there and have an actor take her through,” Bateman says. “You think, ‘If it’s bad for me, imagine being her - she’s completely helpless’.

Then he got wedged between some rocks.

“I can remember feeling really hot and thinking, ‘I’m underwater, but I’m sweating’,” he says, as he watched his pulse racing on a wrist monitor. “I could just see my heart rate going up and up and up.

“But the beautiful gift of it was overcoming that... it’s all in your head. It was a really safe environment, so getting over that hurdle of ‘I can do this’ is a small victory each time you do it.”

Howard explains that some of the spaces were so small that despite “a great caretaking... you couldn’t get the safety divers in with them all the time”.

Bateman ultimately had to work himself free.