Carstairs despised the name Betty – a nickname from the press, her real name was Marion – and she preferred to be known as Joe. In 1918 she married Count Jacques de Pret with the sole aim of accessing her trust fund.
The marriage was never consummated, and was annulled when her mother died. After serving in France during the First World War with the American Red Cross, driving ambulances, Carstairs helped to rebury the war dead and also worked in Dublin with the Women’s Legion Mechanical Transport Section (WLMTS).
In 1920, with three former colleagues, she started a female-only garage and chauffeuring service called X-Garage using only women drivers to take guests from the Savoy Hotel and other illustrious settings to the theatre or dinner. When the business closed, she had her first powerboat built after inheriting a fortune from her mother’s side from Standard Oil (now Esso).
The boat was named Gwen, after one of her lovers. Over the next five years Carstairs won several illustrious competitions including the Duke of York’s Trophy in 1926, the Royal Motor Yacht Club International Race, the Daily Telegraph Cup, the Bestise Cup and the Lucina Cup, but the one she really wanted – the Harmsworth Trophy that Levitt had famously claimed – remained out of reach.
Despite her passion for boating, Carstairs did not spend all her money on herself. She funded Malcolm Campbell’s successful attempt at the land speed record in Bluebird in 1931 to the tune of £10,000.
In 1934, complaining of high taxes in Britain, she bought Whale Cay, a 711 acre island in the Bahamas, built a house and ran it as her own fiefdom where, if anything, her eccentricities were accentuated rather than softened.
Uninvited guests would be met on the beach by her carrying a gun or a cutlass, while some unsuspecting American tourists who rowed ashore one day were taken prisoner and locked up in the lighthouse for the night. “I don’t give a damn about the law,” she is reputed to have said.
There was a constant parade of famous visitors to the island, including the Duke of Windsor, who visited several times with his wife Wallis Simpson. During the Second World War, Carstairs had a deep harbour built on the island for the US Navy and when a ship was torpedoed nearby she led a night-time rescue of 46 US sailors.
Assuming it was a man who had been their saviour, it was only when they arrived in Nassau in daylight that they realised she was actually a woman. Openly lesbian, and often dressing in men’s clothes, with tattoos on her arms and a love of cigars, Carstairs had affairs with some of Hollywood’s biggest stars including actresses Marlene Dietrich and Greta Garbo.
She also had a relationship with Oscar Wilde’s niece Dolly, a fellow ambulance driver in the First World War. The main man in Carstairs’ life was a doll named Lord Tod Wadley; a gift from one of her lovers, she bought clothes for him from Savile Row. When she died, aged 93, in Florida, the doll was cremated along with her.