The idea was not new, and its track record was poor. During the First World War, Roger Casement went into the prisoner-of-war camp at Limburg an der Lahn to raise an Irish Brigade from nationalist-minded Irishmen serving in the British Army. Between Casement's efforts and the full weight of the Imperial German Army, fifty-two men signed up. Twenty-five years later the Germans tried again. Abwehr II — the branch of German intelligence responsible for sabotage and for cultivating the disaffected in enemy countries — saw Ireland as a soft flank against Britain, and after the fall of France in 1940 it had a great many British Army prisoners to sort through. The impulse may have come from Seán Russell, then IRA Chief of Staff, who spent that summer in Berlin proposing a new Irish Brigade. The old republican formula — England's difficulty is Ireland's opportunity — was a phrase the Abwehr knew how to use.

The pitch was deliberately vague. Helmut Clissmann, an NCO from the Brandenburgers, the Abwehr's commando unit, later described it plainly: all Irishmen in prisoner-of-war camps were invited to give their names with a view to going to a special camp offering better conditions. That camp was Stalag XX-A (301), in the Brandenburg countryside near Friesack, about sixty kilometres west of Berlin. The offer said nothing about sabotage. The Germans assumed that Irish reunification was common ground they could stand on, and that men who knew the country could guide troops or plant charges if Britain or Ireland were invaded. They also assumed, correctly, that the volunteers would include informers, moles, and men who simply wanted out of a POW camp. Every candidate was interviewed by Clissmann and by Frank Ryan, a former IRA man whose release from a thirty-year sentence in Franco's Spain the Irish government had helped arrange — though whether Ryan cooperated is disputed.

The arithmetic of the vetting tells the story. In December 1940 the initial pool drawn from the entire Stalag network was a little over one hundred men, all claiming Irish nationality, fewer than five of them officers — and those officers stated flatly that they would fight only if British troops invaded Ireland, a scenario being planned at that very moment under the codename Plan W. By spring 1941, when Dr Jupp Hoven arrived at Friesack with a reputation as an expert on Irish affairs, the recruiting base stood at eighty. From those eighty the Germans identified ten men they believed were sincere. To hide the arrangement from the other prisoners, the Abwehr staged a prison break in mid-September 1941 to spirit John Codd and Frank Stringer out; James Brady, Thomas Cushing, William Murphy, Patrick O'Brien and Andrew Walsh followed just before Christmas.

In Berlin the men were housed together and put through the Abwehr course at the Quenzgut training establishment: improvised explosives, incendiaries, and radio procedure. Three operations in the Abwehr II war diary came out of it. Operation Innkeeper went to Sergeant John Codd of Dublin. Operation Seagull I sent Andrew Walsh of Fethard, County Tipperary — codenamed Agent Vickers — to parachute near Glasgow, assemble a three-man sabotage cell and knock out the power station at Fort William and the hydroelectric works at Kinlochleven. Operation Seagull II sent Fusilier James Brady of Strokestown, County Roscommon, into Northern Ireland to recruit IRA members against military targets. None was ever carried out. Walsh's conversation with Cushing killed Seagull I before the agents left for Norway, and Seagull II died alongside it.

The one man who did get sent was James Cromwell O'Neill of County Wexford, a civilian taken off an interned freighter and codenamed Eisenbart. Dispatched to spy in Northern Ireland in the summer of 1942, he turned himself in on reaching London. Back in Germany the operation folded inward. Murphy, O'Brien and Walsh were arrested in September 1942 and sent to Sachsenhausen in February 1943. Walsh survived the war, was handed to the British, and was never charged. Others went the other way: Brady and Stringer volunteered for the Waffen-SS, and Codd went on to work for German and then SS intelligence. The camp was dissolved, and the men who had passed through it were scattered to the Eastern Front or into concentration camps after 1943. It is worth being careful about what these men were: prisoners of war, offered better food and a way out of the wire by a service that held every card. Their choices ran from real collaboration to a con played on their captors — a distinction the Gestapo stopped drawing, and one that landed several of them in the same camps regardless.