The idea for this thesis originated from the author’s position as the leader of the team that was involved with the restoration of a “Quick Firing” 18-pounder field gun Mark II, serial number 9168 in the Irish Defence Forces’ Ordnance Base Workshops. Research carried out for this study confirms that this was one of the guns that were handed over to the fledgling Free State Army in June 1922. The opening shots of the Civil War were fired by an 18-pounder and the gun had an important role during the subsequent fighting. In a broader context the mass-produced 18-pounder was one of the great field guns of the early decades of the twentieth century. Its initial development and subsequent variations were an amalgamation of the great advancements in artillery design and its impact on a small nation like Ireland was therefore significant. This thesis will examine the 18-pounder field gun during its service in the Irish Defence Forces between 1922 and the Second World War.