Coming just after the centenary of the 1916 Easter Rising, Jeffrey Leddin's The labour Hercules: the Irish Citizen Army and Irish republicanism, 1913–23 is a well-researched, comprehensive and highly accessible history of the Irish Citizen Army (I.C.A.). Leddin's account is representative of a renewed interest in, and critical appraisal of, the significance of the Citizen Army and, as such, is the latest in a series of books published to coincide with the centenary of the Rising following a hiatus on the topic of nearly forty years. Unlike his predecessors, Leddin's research has benefitted immensely from the phased release of the online Military Service Pensions Collection from 2014 which has made available 215 I.C.A. pensions application files as compared to the nineteen I.C.A. witness statements previously available through the Bureau of Military History. Leddin, therefore, draws from a much deeper well of first-hand testimony, and one more proximate to the people and events of the revolutionary period providing new information and insights in greater detail.

Leddin's is the first of the recent wave of I.C.A. histories to trace the etymology of the Citizen Army's name and the concept of ‘citizen armies’ per se to the seventh congress of the Second International in 1907. In so doing, he contextualises the Citizen Army's involvement in the 1916 Rising as a phenomenon which arose not just as a nationalist movement, but as a development rooted firmly in previously established international socialist ideology and policies.

Early chapters examine how the pre-constitutional Citizen Army was forged in the fires of the 1913 Dublin lockout and subsequently transformed through the adoption of two constitutions in 1914, initially, under the tutelage of Jim Larkin, Sean O'Casey and Captain Jack White, and, latterly, and more significantly, under James Connolly. This metamorphosis saw it evolve from a strikers’ defence corps for its parent trade union the I.T.G.W.U., weakened and adrift following the conclusion of the lockout, into a stronger body numerically and militarily. The I.C.A. was now imbued with a clearly defined set of social and political ideals such as equality, separatism and socialist republicanism, framed within the pre-eminent goal of national and economic liberation, to be achieved by martial means. In this, Leddin identifies a natural delineation in the Citizen Army's development which was marked, thereafter, by adding the prefix ‘Irish’ to its name.

As the book's title suggests, Leddin is interested in the I.C.A.'s relationship with the broader republican movement and the Irish Volunteers, in particular, given the I.C.A.'s increasing emphasis on republican goals. Leddin posits that O'Casey's resignation and the subsequent split in the volunteer movement over Irish Parliamentary Party leader, John Redmond's support of the British war effort in September 1914 allowed for an alignment of the I.C.A. and those Irish Volunteers who broke with Redmond. The Irish Republican Brotherhood (I.R.B.) recognised this by seeking greater cooperation with the I.C.A. which now under Connolly's leadership, following Larkin's departure for America, was reciprocated through joint participation in a series of commemorations and funerals such as that of O'Donovan-Rossa on 1 August 1915. Relations were cemented by Connolly's co-option in January 1916 on to the I.R.B.'s military council, the body which planned the Rising, with Connolly declaring on its cusp that both militias had been subsumed within a single body, namely, the army of the Irish republic – the I.R.A. Meanwhile, a corresponding and gradual separation occurred between the I.C.A. and the I.T.G.W.U., the latter fearing British retribution.

In the remaining chapters Leddin focuses on the I.C.A.'s role in the Rising by reference to the three Dublin garrisons where it saw action. He also examines the re-establishment of the I.C.A. as a distinct and autonomous body after the Rising and assesses its supporting role during the War of Independence and the Civil War. Leddin, interestingly, explores the possible reasons for the I.C.A.'s secondary role to the Volunteers and its perceived military inertia during this period, measuring such claims against the evidence. Using I.C.A. members’ military service pensions Leddin records their view that the widespread arrests of anti-Treaty soldiers, by the Free State army, which followed an operation known as ‘the Night of the Bridges’ on 5 August 1922, effectively left the I.C.A. decimated and marked the end of its military capacity from that point onwards. Leddin concludes with an assessment of the I.C.A.'s legacy with regards to socialist republicanism spanning the Republican Congress of 1934 up to the Official I.R.A. in 1969 and, more recently, the I.N.L.A., both organisations (that is, the Official I.R.A. and the I.N.L.A.) having expropriated the I.C.A.'s political and ideological mantle. Based on new sources, Jeffrey Leddin's contribution to the topic is, arguably, the most extensive undertaken to date since R. M. Fox's seminal work The history of the Irish Citizen Army was published in 1943 and so will prove indispensable to casual reader and historian alike.