On the night of 26 April 1974, 19 prized masterpieces were stolen at gunpoint from Russborough House, County Wicklow, the home of Sir Alfred Beit, a former Conservative MP and South African mining heir.

The haul included paintings by Goya, Velázquez, Vermeer, Rubens, Hals, Gainsborough and Guardi. It was one of the largest art heists in history. The IRA gang had tricked their way into the stately home south of Dublin, led by a woman pretending to be a French tourist whose car had broken down.

Rose Dugdale, who has died aged 83, may have started out as an Oxford-educated debutante and heiress but her unconventional life spiralled through political activism into republican violence, culminating in her developing explosives to destroy Royal Ulster Constabulary armoured Land Rovers. A privileged renegade, she has been compared to contemporary, 1970s ultra-leftist revolutionaries such as Patty Hearst, Italy’s Red Brigades and the Baader-Meinhof gang.

Earlier in 1974 she had carried out the IRA’s first helicopter-bomb attack on a Northern Ireland police station. The aircraft had been hired in County Donegal by a woman posing as a freelance journalist for a photographic assignment.

Once airborne, the pilot was threatened with a pistol and ordered by Dugdale and her accomplice, Eddie Gallagher, to collect milk churns packed with explosives and then fly over the border. One device was then dropped on the RUC station in Strabane, County Tyrone; the main charge failed to explode. No one was injured.

The Wicklow heist was not Dugdale’s first art theft. Knowledge of classical painting acquired in her youth had proved useful. In 1973, she broke into her parents’ home in Devon with professional burglars and looted £80,000 worth of pictures, silver and antiques to raise money for revolutionary causes. She was subsequently given a two-year suspended sentence by a judge, who said it was unlikely she would reoffend.

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The aim of the raid on Russborough House, her idea, was to ransom paintings for the return from an English jail to a Northern Irish prison of four hunger-striking IRA bombers – Gerry Kelly, Hugh Feeney and the sisters Dolours and Marian Price.

After the servants were rounded up and Sir Alfred was beaten, everyone was tied up. Dugdale, maintaining the character of a French tourist, went from room to room pointing at pictures. “Zis one and zis one! Non. Not zat one!” according to Sean O’Driscoll’s 2022 biography Heiress, Rebel, Vigilante, Bomber: The Extraordinary Life of Rose Dugdale. Gallagher and two other IRA men loaded the paintings into the car.

They drove to the west Cork village of Glandore, where she had booked a cottage under the name of Ms Merrimée. A ransom note was sent to the National Gallery of Ireland in Dublin. After that the plot began to unravel.

The Price family called for the paintings not to be damaged. Dugdale opened the door to Garda officers using her false French accent. They were not convinced by her explanation and raided the cottage to discover canvases estimated to be worth around £100m at today’s valuations.

Dugdale was born at Yarty Farm, her family’s 600-acre estate in east Devon. Her father was Lieutenant Colonel Eric Dugdale, a successful Lloyd’s underwriter, whose main home was in Chelsea in London. Her mother, Carol (nee Timmis), was from a wealthy Gloucestershire family; she had studied art and initially married Oswald Mosley’s younger brother John; they had two sons but divorced over his womanising. She subsequently married Dugdale, with whom she had three children.

Bridget Rose was the middle child. Despite her first name she had no immediate Irish ancestry and was known as Rose. She attended Miss Ironside’s school for girls in Kensington.

In an early display of characteristic resolve, she initially resisted becoming a debutante but struck a deal with her family – agreeing to be presented to the Queen at Buckingham Palace in return for being allowed to apply to university. The 1958 “coming out” season, where young women were launched into high society, was the last ceremony hosted by the monarch.

Dugdale went to St Anne’s College, Oxford, in 1959 to study philosophy, politics and economics, graduating three years later. Among her tutors were the novelist Iris Murdoch and Peter Ady, a female economist with whom she had an affair.

Her first confrontation with the establishment came when she and another student dressed as men to infiltrate the then all-male Oxford Union debating society, as part of a campaign that later led to the admission of women to full membership in February 1963.

She took a master’s degree in philosophy at a US college, returned to London to work as a government economics adviser on developing countries with Ady in 1965, then completed a doctorate at Bedford College, London, where she taught economics.

The 1960s countercultural revolution broadened her horizons. Dugdale travelled to communist Cuba and to Belfast, where she witnessed the army on the streets. Radicalisation followed. She left academia in 1971, deciding that she wanted to give away her inherited wealth to the poor.

Using her own money, she set up a north London claimants union office supporting marginalised people. She fell in with Wally Heaton, a former soldier who urged her to become involved in armed revolution.

Bloody Sunday in January 1972, when the Parachute Regiment shot dead 14 civil rights protesters in Derry, was a watershed. She and Heaton travelled there, met IRA leaders and offered them money to buy weapons. She returned repeatedly to Belfast and Derry, delivering guns she had obtained.

Heaton was jailed for the raid on Dugdale’s parents’ home and in 1973 she met Gallagher, who had volunteered to work in her claimants union office. They teamed up and later that year moved to Ireland where she joined an IRA training camp.

If her earlier years had an air of political theatrics, her later years showed more deadly intent

Following the Russborough House raid, Dugdale was sentenced to nine years in prison for the Strabane hijacking and the art theft. She was held in Limerick jail, where it was eventually noticed that she was pregnant. The father was Gallagher.

The following year, Gallagher, who was on the run, kidnapped the Dutch industrialist Tiede Herrema in Limerick. The IRA gang demanded the release of Dugdale and two other republican prisoners within 48 hours, warning that Herrema would be shot.

Irish police tracked down the kidnappers. After an 18-day siege they surrendered. Herrema was unharmed. Gallagher was sentenced to 20 years.

Even in prison, Dugdale kept up the pressure – forcing the authorities to allow her and Gallagher to marry behind bars in 1978 so that she could avoid extradition to the UK. She was freed in 1980 and moved to Dublin to raise her son, Ruairí.

If her earlier years had an air of political theatrics, her later years showed more deadly intent. She worked with residents’ vigilante groups to drive heroin dealers out of inner-city estates. She also broke up with Gallagher and lived with Jim Monaghan, an expert IRA bomb maker.

Together they helped refine the Provisionals’ weapons technology, conducting research on a remote farm in County Mayo. Their improved missile launchers – which used digestive biscuit packets to absorb the recoil – and fertiliser-based bombs enabled the IRA to kill more soldiers, RUC officers and civilians.

She never expressed regret. “The happiest day of my life was the bombing in Strabane,” she told the author Sean O’Driscoll. “It was the first time I felt at the centre of things, that I was really doing as I said I would do.” A feature film based on her life, Baltimore, focusing on the Wicklow art raid, is due to be released in the UK on 22 March.

Dugdale, who had been living in a Dublin care home run by nuns, is survived by her partner, Monaghan, by Gallagher, to whom she remained married, and by Ruairí.

Bridget Rose Dugdale, academic and IRA member, born 25 March 1941; died 18 March 2024

This article was amended on 19 March 2024 to clarify the chronology of women’s admission to the Oxford Union debating society. Additionally, an image was removed as it showed a vehicle used in a different robbery at Russborough House.