Jane Fonda is famous for plenty things. Writhing around in wet-look silver as a coquettish space traveller in thigh boots for Barbarella. Lunging and reaching through aerobics workouts, shrink-wrapped in Lycra leotards and building up her own fitness empire. Waltzing her way to an Oscar nomination in They Shoot Horses, Don’t They?. And wisecracking in Nine to Five alongside Dolly Parton and Lily Tomlin. But her haters remember Fonda most for an ill-advised move she made during the Vietnam War.

On a 1972 visit to a Hanoi military base, she sat down on an anti-aircraft gun. It belonged to the Vietnamese, and was designed to shoot US soldiers. Perched there, with ammunition piled at her feet, Fonda laughed, pulled goofy faces, winked, clapped her hands, and joked with Vietnamese people around her. She’d been a staunch anti-war activist for a couple of years by that point, and part of the FTA (‘Fuck the Army’) travelling sketch troupe with Donald Sutherland.

This was the last straw. When photos got out, it was taken as her petulantly flipping the bird to the US military, and anyone who supported it. Soldiers called her ‘Hanoi Jane’ and it stuck. Cadets at the US Naval Academy learned to chant ‘Goodnight, Jane Fonda!’ and the whole company would shout back ‘Goodnight, bitch!’ Even now, a Google search throws up pages of hate-filled posts about the ‘whore of communism’ and her ‘ugly little mouth’.

‘It was a terrible, terrible mistake,’ says Anne Archer, who’ll be playing Fonda in a new Fringe drama which focuses on her controversial anti-Vietnam activism. ‘The whole country was protesting and not just the hippy movement: everyone was rebelling against the war. I don’t care how tired she was, she shouldn’t have sat on that tank. But she regrets it, and she says she will regret it until the day she dies.’

The Trial of Jane Fonda zooms in on a later event during the 1980s, where Fonda was in Connecticut, faced with irate Vietnam vets who tried to stop her filming the movie Stanley & Iris. It was her co-star Robert De Niro who suggested she met with them in an attempt to defuse things. That sit-down is the crux of this new play, and helps unravel how a hot property celebrity of the time got drawn into a war of spin, political protesting and accusations of treason: on both sides.

‘It becomes pretty apparent that she was used,’ shrugs Archer, a sage mix of calm, reticence and softness, who you may recognise as the docile brunette that Michael Douglas cheated on in Fatal Attraction, or Harrison Ford’s surgeon wife in Patriot Games. ‘How can we say for certain that that day with the gun wasn’t a stunt or a trap?’ says Archer. Like her husband Terry Jastrow, who wrote and directed the play, she’s done her homework into Fonda’s life, using an especially fine-toothed comb to run through that day at the army base.

‘Jane wasn’t the only one protesting; everyone was speaking out, but she was particularly famous at that time. She was Henry Fonda’s daughter and she’d just won an Academy Award [for Klute]: the press would grab at anything she’d do.’

Archer, who founded and runs Artists for Human Rights, which raises awareness for the UN Universal Declaration of Human Rights, believes Fonda was just a propaganda pawn, someone in the limelight who needed to be publicly brought down a peg or two after speaking out against the war.

‘Jane herself admits she is someone who was eager to please, especially the men in her life: her father, her husbands,’ says Archer. ‘On that day, she had told her guides three times that she didn’t want to visit a military installation. They insist, she doesn’t want to disappoint, she’s exhausted, she agrees: suddenly there are film crews around which haven’t been there before. If it hadn’t happened to her, they’d have found someone else. When you live to hate, there’s always someone to target.’

Jastrow wrote to Fonda about his plans to make a movie about her activism, but she tried to talk him out of it. LA film producers took one look at his screenplay and dropped the ‘hot potato’. Jastrow wasn’t listening and decided to bring a world theatre premiere to Edinburgh. He hopes that his combination of research (he tracked down Fonda’s guides and interpreters in Hanoi, and stayed with the actress at her Santa Fe ranch), plus his leading lady (‘Anne Archer is a class act, world class’, he beams about his wife) will give this story the clout it needs to go down well with Fringe audiences. Ultimately, he hopes it will make it to the West End.

‘Vietnam was the first televised war,’ Jastrow explains. ‘That in itself interests me, but the issues Jane’s story brings up are universal and timeless. We saw them again with Iraq and North Korea, and we’ll keep seeing them. America considers itself a country where we permit dissent, free thought, and freedom of speech. Does opposing war make you a peacemaker or a traitor? I know some sleeping dogs should be left to lie, especially when they are very vicious, aggressive ones. But it’s only by looking at our past that we stand any chance of not repeating it.’

The Trial of Jane Fonda, Assembly Rooms, George Street, 0844 693 3008, 1–24 Aug (not 11), 4.05pm, £16 (£13). Previews 30 & 31 Jul, £10.