British Spies and Irish Rebels provides a well-written and impressively researched narrative history of British intelligence concerning Ireland between 1916 and 1945. Using many records only recently released to the British National Archives and a wide variety of other sources where official ones are still lacking, Paul McMahon sheds considerable light on a subject that has until recently been little studied. Well-organized and complete, if at times too methodical, this book expands upon McMahon's Cambridge PhD dissertation (under the direction of Christopher Andrew and Neville Wylie).

Part 1 covers the “Irish Revolution” from 1916 to 1923, but the most original and enlightening material examines the state of British intelligence in Ireland after the truce of July 1921. McMahon points out that when Britain lost its means of gathering systematic intelligence in the south of Ireland, alarmist dispatches from loyalists filled the void. This almost led to disaster when shortly after the assassination of Sir Henry Wilson, Winston Churchill used one such report to justify military intervention against the Irregulars. Cooler heads prevailed, but nagging doubts about the stability and trustworthiness of the Irish government remained. Although British leaders were reassured by the Irish government's firm handling of the security situation and ongoing cooperation in combating IRA gunrunning, intelligence reports detailing Irish-American conspiracies, Bolshevik connections to the IRA, and involvement in the violence in Northern Ireland ensured that British anxiety would not ease with the end of the civil war.

McMahon's analysis of the interwar period, from 1923 to 1939, stresses the limitations of British intelligence work in Ireland. Intelligence services in general suffered from neglect during the 1920s, but the Irish situation was particularly acute because of the Irish Free State's unique constitutional position. Unlike other dominion governments, the Irish never fully cooperated with Britain on military and intelligence matters, yet because Ireland was part of the empire, the British could not post an ambassador to Dublin. Hence, British leaders lacked even the most basic political intelligence about the situation in the Free State. Forced to rely upon alarmist reports from an informal network of remaining unionists in the south and paranoid loyalists in the north, the British government feared the Free State government would be overthrown by a resurgent IRA or subverted by widespread communist infiltration. Nevertheless, after the expected crisis over the Boundary Commission failed to materialize in 1925, the British were happy to ignore Ireland almost altogether—so much so that they were shocked by the rise of Fianna Fail in 1932. With Eamon de Valera in control, British rulers expected political and social collapse as well as republican aggression toward Northern Ireland or mainland Britain. These fears, magnified by continued failure to collect reliable intelligence within Ireland, resulted in a “spectacularly unsuccessful policy” (239) of sanctions and pressure, which only strengthened de Valera's position. Even after the international situation forced a more conciliatory stance, de Valera cleverly played upon continued British anxieties to advance his argument for the return of the Treaty Ports.

In part 3, McMahon shows that Irish neutrality during World War II required a considerable expansion of British intelligence in Ireland. To combat a feared Irish “fifth column” of Irish fascists and republicans who stood ready to aid the German invasion, Britain relied on a “dual intelligence approach” (343), combining clandestine operations and close cooperation with the Irish government on military and intelligence matters. The Secret Intelligence Service (SIS) and other intelligence agencies established new secret networks of agents. But more important, the new British political representative in Dublin and military and intelligence attachés worked with Irish authorities to provide the necessary operational intelligence and to dispel the myth of the Irish fifth column.

After the initial crisis passed, British intelligence work focused on winning the propaganda war in Ireland and on preventing any vital defense information from leaking out through Ireland. The colorful cast of intelligence-related characters makes McMahon's story interesting, although his assessment that confiscating German Ambassador Hempel's infrequently used wireless transmitter before D-day was “the most serious challenge faced by British intelligence agencies” (402) suggests the limited importance of this theater of operations.

McMahon's examination of World War II intelligence seems to confirm an unspoken theme of the entire book: that secret intelligence—the cloak-and-dagger aspects of the business emphasized in popular histories—was essentially worthless, at least in Ireland. Only after 1941 did the SIS provide reliable intelligence, which tended to debunk rather than spread alarming rumors, but even then its agents were untrained locals, its information was seldom original or important, and its network was thoroughly penetrated by Irish intelligence forces. This modest achievement marked a huge improvement over the exaggerated and alarmist prewar secret intelligence, which tended to originate from embittered unionists dreaming of the whole of Ireland returned to British control or from mercenary agents angling for money or more permanent employment.

McMahon's contention that intelligence had a “major impact on British decision makers” (3) is less convincing. The extent to which intelligence affected decisions is never clear. McMahon himself points out that “diehard unionist” (163) views were prevalent among the intelligence forces and Conservatives leaders. Arguably, then, intelligence served only to confirm or reinforce preconceptions and biases. For instance, I doubt Churchill's prejudices were (or could be) overcome by the calming intelligence reports that cautioned against coercion in 1940. He was perfectly willing to cherry-pick the intelligence to find material to support his position.

Similarly, McMahon probably gives British intelligence too much credit for changing official attitudes toward Ireland by the end of World War II. The changed geopolitical circumstances more profoundly shaped Britain's new relationship to its neighbor than did the levelheaded reports from the British representative in Dublin. Unionist diehards had to reconcile themselves to far greater threats to empire than an independent Ireland. Neither of these reservations detract from McMahon's accomplishment. His book is an important contribution to the scholarship of intelligence, and a worthy first volume in the Boydell Press History of British Intelligence series.