THE film industry is full of stories showing just how far actors go to get into character.

For Brighton actress Kirsten Callaghan, the method is simple but by no means easy... swimming.

The 28-year-old is starring as record-breaking Brighton swimmer Mercedes Gleitze in Vindication Swim, charting the forgotten pioneer’s efforts to battle a damaging hoax threatening to sink her claim as the first British woman to swim the Channel.

Kirsten and Mercedes have a lot in common.

Not only do they look remarkably alike, but they share all manner of coincidences, including experience in the shipping industry.

But it is swimming which best immerses the actress in Mercedes’s world, Kirsten said.

“It’s so special to be able to connect with her physically, getting into the water and pushing myself,” she said.

“It was mainly just getting in the water that got me into character. I’m in the water every single day.

“Last summer I was in the water for up to four hours.

“I found out what it’s like when you’re really cold or when your mouth gets sore from the salt.

“I’ve had swimmer’s claw when you get so cold your hands start to freeze.

“Getting to experience those things like that, knowing the difficulty of what she was doing, is a massive challenge.”

Even now Mercedes’s feats seem superhuman.

Born in Brighton in 1900, she made her name in October 1927 when she swam the Channel in 15 hours and 15 minutes on her eighth attempt.

The swimmer soon got a taste for record breaking and swam the Straits of Gibraltar, the Dardanelles and all around the Isle of Man.

By the time of her retirement in 1932 her record for endurance swimming was 46 hours.

But Vindication Swim concerns itself with its namesake, a stunt undertaken by Mercedes to prove she was the first English woman to swim the Channel.

Days after she completed the original feat, a woman called Mona McLennan claimed she had completed a cross-Channel swim the same week in just 13 hours and ten minutes.

Yet under heavy scrutiny from the press, the challenger soon confessed her swim was a hoax.

This called into question Mercedes’s accomplishment.

So she agreed to do it again to prove her prowess. A “Vindication Swim” was set for October 21.

With her attempt feverishly covered by journalists, actress Kirsten had plenty of material with which to immerse herself in Mercedes’s world.

“There are short Pathe newsreels where I can look at her mannerisms,” she said.

“I was reading extracts of journals she had written.

“She had a shy side but an inner belief. She did struggle with the fame that came with it.

“I definitely feel a connection to her. I’ll be really upset when it’s over.

“I’m doing my take on her life, I’m not impersonating her.”

The meticulous authenticity bleeds into every aspect of the film.

Hove-based director Eliott Hasler, 19, has shot much of the film in Sussex.

Cuckmere Haven, Stanmer House and Eastbourne Pier all feature among other recognisable landmarks.

Filming just wrapped on an authentic Twenties bus at Amberley Museum.

So what is it like to see Sussex as it was nearly a century ago?

“I’ve found a much deeper connection to Sussex,” said Kirsten.

“Before I never knew Amberley Museum existed. I had never been out to Newhaven Fort. I had never explored the Seven Sisters.

“Seeing it from a historical perspective has opened my eyes to how special these places are.”

“I’m always behind the camera so it’s not quite as immersive for me,” said Elliott.

“But Amberley was a rewarding shoot.”

The director says Vindication Swim is only just halfway done. With a completion date set for 2021, there is still plenty of filming to do.

But the wait will certainly be worth it to see Sussex featured so prominently on the big screen, showcasing one of its forgotten heroes.