In July 1936, three Jewish tailors from Stepney set off to cycle to Barcelona. Card-carrying members of the Communist party, Nat Cohen, Sam Masters and Allick Sheller were travelling to the Catalan capital to witness the People’s Olympiad.

The games had been conceived by Spain’s new left-wing government as an alternative to the Berlin Olympics which Hitler was to open the following month.

They would never take place: as athletes and visitors began to pour into Barcelona, General Francisco Franco launched the uprising which plunged Spain into a brutal, three-year civil war and claimed the lives of 500,000 people.

But, like the Jewish team from Palestine which had come to compete in the Olympiad, Cohen and his comrades decided to stay in Spain to help resist the fascist coup.

During the course of the conflict, some 41,000 volunteers from 50 countries joined them in what has been described as ‘the first battle of the Second World War’. Between 6,000 to 8,000 of the recruits to the International Brigades are estimated to have been Jewish, including nearly half of the Poles who went to Spain, over one-third of the Americans, and around 20 per cent of the Britons.

Jews did not only constitute a disproportionate number of the foreign fighters in Spain. It is estimated that 70 per cent of the medical personnel who volunteered to tend the injured were Jewish, with Yiddish often used in operating theatres as a common language.

In some respects, their story is a forgotten one. As military historian Martin Sugarman has argued, ‘the marginalisation of the huge part played by the Jewish fighters in Spain is due to the tight grip held by old-fashioned Stalinists who have been “Keepers of the Memory” of the International Brigades’. In the wake of the 1967 war Poland’s communist government went so far as to destroy memorials to the Botwin Company, a Jewish unit formed in December 1937. Part of the Polish Dombrowski Brigade, it was named in honour of Naftali Botwin, an 18-year-old Polish Jewish communist executed for murdering a secret police informant. Thus the communists’ fierce anti-Zionism and anti-Semitism trumped the reputation for heroism, encapsulated by the nickname ‘the red devils’, earned by the Botwin men.

As Gerben Zaagsma, author of a forthcoming book on Jewish volunteers in the International Brigades, has suggested, their motivations were complex – especially as the situation of Jews in Eastern Europe, for instance, was very different from that of Jews in Britain or the United States. To a degree, the high number of Jewish recruits to the International Brigades was a function of the over-representation of Jews in socialist and communist parties – itself the result of those parties’ opposition to anti-Semitism. But many of the Jewish volunteers simply wanted to fight the growing spectre of fascism. As one recruit to the Abraham Lincoln Brigade, formed by American volunteers, wrote: ‘I am as good [an] anti-fascist as any communist. I have reason to be. I am a Jew and that is the reason I came to Spain. I know what it means to my people if fascism should win (And I know they won’t).’

The motivations of others were less easy to discern. George Nathan, a working-class Jew from the East End of London who joined the elite Brigade of Guards during the First World War, was, writes David Boyd-Hancock in his book I Am Spain, ‘hardly a stereotypical British army officer’. Indeed, he left the military after hearing fellow officers discuss shooting ‘dockland scum’ during the General Strike and, penniless, drifted between jobs. Travelling to Spain he reinvented himself as the army officer he had once been and, in the word of an admiring colleague, ‘found his place in the International Brigade. Everything he had learned in his old life took on a new meaningfulness’. Respected for his competence, Major Nathan became chief of staff to the commander of the XV International Brigade. Further promotion, however, escaped him because he refused to join the Communist party, although membership may have been denied him on account of his sexual orientation and unwillingness to feign ‘great political enthusiasm’. Nathan died fighting with the men of his British battalion during the battle of Brunete in July 1937. With his gold-tipped swagger-stick in his hand, nonchalantly ignoring their perilous position and trying to show ‘the crumbling Spanish infantry that holding on was easy’, Nathan was hit by a bomb splinter and buried beneath olive trees on the banks of the Guadarrama.

Even for those Jews who were committed communists, the brutality of Stalin’s henchmen in the Brigades was enough to shake the faith of many. Born William Horvitz, the novelist William Herrick was a self-declared ‘red-diaper baby’. His parents – who had fled Tsarist Russia – were members of the American Communist party who hung pictures of Lenin, Stalin and Trotsky in their home. Their son was active in the Young Pioneers and later risked his life trying to organise black sharecroppers in the Deep South. Unsurprisingly, Herrick was among the first 100 US recruits to heed the party’s call to fight in Spain. As their train left the Gare de Lyon bound for Barcelona, he recalled, the recruits sang the Internationale and the Hatikvah. While ‘anxious to get into the ring’, Herrick was severely wounded on only his second day fighting. Recuperating in hospital, he let slip to a nurse his growing doubts about the party. Betrayed, he was taken to a church which had been turned into a prison to witness a communist execution squad ‘coolly put to death three Spanish leftists’. The scene – intended as a warning – haunted him for the rest of his life and inspired his book, Hermandos!, which has been described as ‘the fictional counterpart to Orwell’s Homage to Catalonia’.

For others, reality dawned more slowly. Moishe Stern, a Ukranian Jew who was an operative in Soviet military intelligence, arrived in Spain in September 1936 using a forged Canadian passport, adopted the name Emilio Kléber and became second-in-command to the International Brigade’s communist commander André Marty. Initially feted in Soviet propaganda as the ‘Saviour of Madrid’ for his role in leading the XI International Brigade’s effort to save the Spanish capital from a Nationalist assault in November 1936, Kléber later fell foul of the jealousies and paranoia which wracked the Brigades’ upper ranks. Stripped of his command following later military setbacks – in truth, argues Anthony Beevor, he never ‘exceeded the level of a tough First World War commander who was unsparing with the lives of his men’ – Kléber was sentenced to 15 years hard labour. His name removed from Soviet histories of the civil war, he died in a Soviet gulag a year after Stalin’s death.

The war also acted as a magnet for adventurers, like André Friedmann and Gerda Taro, a young Jewish couple living in Paris. Exiles from the Nazis and both aspiring photojournalists, they had invented the persona of Robert Capa after Friedmann found his Jewish-sounding name a bar to selling pictures to the press. Although its authenticity was later questioned, his image The Falling Soldier, purporting to show a Republican militiaman at the moment he was shot dead by a sniper, led to international acclaim with Picture Post naming Capa the ‘Greatest War Photographer In The World’. No longer selling her work under Capa’s pseudonym, Taro’s pictures of the conflict also began to appear in the international press. Her life was cut tragically short when, covering the Battle of Brunete alone in July 1937, Taro was killed in a collision between the car she was travelling in and a Republican tank. She thus became, in the words of Life, ‘probably the first woman photographer ever killed in action’. Despite his grief, Capa remained in Spain, photographing the International Brigades’ leaving parade in Barcelona in October 1938. The city fell to Franco’s forces three months later, marking the effective collapse of Republican Spain.

Like George Nathan and Gerda Tero, Sam Masters was also to become a victim of the Battle of Brunete. His bicycling comrade, Nat Cohen, fared rather better. After taking part in a failed attempt to prise Majorca from the hands of the rebels, Cohen – who had fought Mosley’s Blackshirts on the streets of the East End – returned to Barcelona and began to assemble the Tom Mann Centuria, the first, albeit short-lived, effort to bring together other British volunteers who had signed up to fight for the Republic.

Injured in battle, Cohen fell in love with a Spanish nurse, Ramona, who he was determined to bring home with him. When he was repatriated, Cohen managed to smuggle her out with him to Paris, but he still faced the dilemma of how to get Ramona into Britain. He hatched a plan with an East End comrade-in-arms, Joe Jacobs and his wife, Pearl. The Jacobses travelled to France and met up with Cohen and Ramona. Pearl then returned to Britain posing as a day tripper, while Cohen’s future wife arrived in her new homeland using Pearl’s passport.