Having fought alongside each other with great success at the Battle of Messines, 7th June 1917, The 16th (Irish) and 36th (Ulster) Divisions again fought side by side at the Battle of Langemarck, 16th August 1917. On that occasion however, there was to be no success, and instead an unmitigated disaster ensued resulting in both Divisions being decimated.In this fascinating account, the causes of the failure to exploit the undoubted success of the Messines offensive are examined in the context of being contributary factors to the delay, and underachievements, which marked the beginning of the Third Ypres Offensive. These include a general lack of urgency, misunderstandings, and a lack of clarity over tactical objectives at Command level, the mismanagement of Artillery, Tank and Infantry resources, and the failure to understand the geography of the battlefield.The delay that ensued enabled the German defenders to accelerate the construction of reinforced concrete bunkers and pill boxes which were to have such an important role in the outcome of the battle. The development and methods of construction of these defenses is analyzed in the narrative, as it assists in showing the extent of the German defenses faced by the Irish.The opening of the Third Ypres Offensive is investigated, as the failure to make a breakthrough on 31 July 1917, led to the unplanned relief of the attacking Divisions of XIX Corps by both Irish Divisions, as the 55th (West Lancashire) and 9th (Scottish) Divisions were exhausted by their experience.This relief ensured that 16th and 36th Divisions held the front line for two weeks prior to their attack on 16th August, in horrendous weather conditions and under constant German shelling. This led to all the attacking battalions being weary, and the majority under half strength, when the advance began.The day of the battle is examined in detail from the perspective of each of the attacking battalions, utilizing official histories, war diaries, maps, and personal accounts so that a coherent picture of the events of that fateful day are revealed for the first time in print. The Regimental Histories of the German defenders have also been obtained to establish the German perspective of the battle. Analysis of the severe casualties suffered by the Irish Divisions is included to emphasize the devastating nature that the Battle of Langemarck had on both Divisions and on many homes across the island of Ireland.The post-battle controversial comments of the Commander Fifth Army, General Sir Hubert Gough, concerning the performance of the Irish Divisions are analyzed in detail to prove that these comments were ill-advised and a poor attempt to deflect blame from the shortcomings of Fifth Army command.This valuable account highlights the bravery and tenacity of the Irish soldier in a battle where they were badly let down by the deficiencies of those in command of the British Fifth Army.