Published between 1918 and 1933, An t-Óglách is an incredibly important resource providing insight into the Irish Republican Army (IRA) and National Army’s understanding of Irish masculinity. Printed as a military journal by the IRA during the War of Independence, and the National Army during the Civil War, An t-Óglách contains a wealth of information beyond its surface function as a tool of strategic and tactical instruction, and as a source of propaganda. This thesis explores the intricacies of An t-Óglách’s wartime editions, examining the journal’s construction of masculinity. The historiography of the War of Independence and Civil War offers limited analysis regarding masculinity and the IRA and National Army’s conception of masculinity. Using An t-Óglách to discern the IRA and National Army’s understanding of masculinity, this thesis argues that An t-Óglách’s construction of ‘true’ collective Irish manhood was a continuation of nineteenth century understandings of masculinity and an appropriation of British notions of manhood. Looking at militarism, linguistics, and athletics, this thesis contends that An t-Óglách viewed the IRA and National Army’s engagement in physical force and cultural nationalism as acts of performative masculinity, which revealed the IRA and National Army’s conception of masculinity to be a complex dialectic of anti-colonialist rhetoric and British appropriation.