Ever since he had first visited the Pamplona bull runs, Ernest Hemingway was fascinated by Spain—it informed his best work, including The Sun Also Rises and For Whom the Bell Tolls.

The latter is set during the Spanish Civil War, in the late 1930s, with the volunteer fighter Robert Jordan as its protagonist. Jordan gives up his life for a cause close to Hemingway’s heart: that of the Democratic Spanish Republic, whose elected government finally lost a three-year war on April 1, 1939, to Fascist-backed rebels led by soon-to-be dictator Francisco Franco.

Hemingway, then aged 37 and seeking to reinvigorate his life with a dose of danger, reported from the battlefield, where he could see that Hitler and Mussolini were using Spain as a “dress rehearsal for the inevitable European war,” as he told his parents-in-law in a letter written on February 27, 1937. He denounced Roosevelt’s non-intervention policy as cowardly and became an admirer of a volunteer army called “the International Brigades,” which was fighting to defend Spanish democracy.

The Brigades brought together 35,000 men and women from 85 countries, speaking two dozen languages and united against autocracy in Spain. Contemporaries compared the group to the medieval Crusader armies.

Some 2,800 American volunteers fought in the International Brigades’ Abraham Lincoln battalion, while others—such as Hemingway’s fictional Robert Jordan—were guerrilla fighters who carried out daring missions behind the lines.

Jordan’s character has long been thought to have been based on the writer’s own experiences. Was there a chance, I started to wonder, that Hemingway had been a secret member of the volunteer army he so admired?

Mission Impossible

When I began writing a history of the Brigades, that seemed a preposterous idea. Hemingway has been a source of fascination for nearly a century—his participation in the war that gave him Robert Jordan would surely be public knowledge by now.

Journalists cover the Spanish Civil War, 1937. Hemingway is the one at center with the mustache.

And yet, in a little-known note sent to the poet Edwin Rolfe kept at the University of Illinois at Urbana-Champaign and ignored by Hemingway scholars, the writer claims to have led a dangerous behind-the-lines mission himself. The note is written in bullish Hemingway shorthand, and details an attempt to organize a revolt in an unnamed, enemy-occupied town where he had friends from his previous trips to Spain. Hemingway admits that he was “scare[d] pissless all the time, really scared,” as he thought about the indignity of being captured and shot. His report after returning, which stated that the proposed uprising would not work, was deemed “defeatism of the deepest dye” by those who had sent him, or so he claims.

No other proof of Hemingway’s actually taking part in the war he catalogued so passionately survives.

The famously boastful writer was going through several crises at the time—in his writing (eight years had gone by since the spectacular success of A Farewell to Arms), popularity with critics who claimed he was ignoring the pressing social issues of the day, and a crumbling marriage to second wife Pauline Pfeiffer. In Spain he was seeking literary inspiration, time with his lover Martha Gellhorn, and what Josephine Herbst termed “a definite call … to be the war writer of his age.”

In Madrid, the front was a short stroll away from Hemingway and Gellhorn’s room at the Hotel Florida. “No matter how often you do it,” wrote Gellhorn, “it is surprising just to walk to war, easily from your own bedroom where you have been reading a detective story or a life of Byron.”

The mostly left-wing, radical volunteers that made up the International Brigades had mixed feelings about Hemingway. He “had the calming effect of a buffalo straying shaggily over the tundra,” wrote German commissar Gustav Regler. “For him we had the scent of death, like the bullfighters, and because of this he was invigorated by our company.”

Lincoln commander Milton Wolff considered him a “tourist” and a “prick” who “wants very much to be a martyr,” while fellow Lincoln brigadier and future Hollywood scriptwriter Alvah Bessie found him generous to friends but also “cruel, petty, a braggart, a bully, an anti-Semite and a permanent adolescent.”

When the depleted Brigades were disbanded, in 1938 (by which point nearly half the volunteers would be dead or injured), Gellhorn found the normally robust Hemingway in tears. “I really did love E. then and it had a long influence on me,” wrote Gellhorn, who soon became his third wife.

Hemingway wrote a tender elegy to the American volunteers, declaring that “no men ever entered earth more honorably than those who died in Spain.” Peter Carroll, the historian who discovered the note and brought it to my attention after literary scholars had failed to spot it, told me he thinks it “conveys an authentic experience.” But whether Hemingway ever really matched the bravery of Jordan and the International Brigades’ volunteers remains a mystery.

Giles Tremlett’s The International Brigades: Fascism, Freedom and the Spanish Civil War is out now from Bloomsbury