The aim of this thesis is to highlight the service of ex-British soldiers in the Irish Army and to examine some of their experiences during the period 1913-1924 with particular emphasis on the Irish Civil War. There was a constant utilisation of ex-British servicemen for their skills and also their intimidation by republicans throughout the period but their involvement may have been one of the factors that helped the IRA to bring the British government to negotiate. This is also true for the Free State Army and its defeat of the IRA during the Civil War. The Irish Volunteers and IRA was a guerrilla force combating a conventional army in many cases by using British military skills learned from ex-British soldiers. The Free State Army fought the IRA, which it had also evolved from, portraying a conventional military force using many more ex-British soldiers and lessons they had learned from the War of Independence against the British and those learned during the Great War. The ex-British soldiers helped to transform the army from a guerrilla force into a conventional army and it was probably their impact that had the greatest influence on the Irish Free State Army in defeating the republican forces and helped win the Irish Civil War. The fact that the Free State government and the new establishment were seen as pro- British, seen to be supported by the British with a constitution incorporating a pledge of allegiance to the crown was exasperating to republicans. They saw the National Army as crown apparatus and the recruitment of ex-British servicemen, their former enemies as further evidence of this. The attitudes of republicans towards exservicemen in Ireland and especially those in the army during the Irish Civil War and the impact of ex-British soldiers on the evolution of the Irish Volunteers and Free State Army has to a great extent been forgotten in Irish nationalist and military historiography.