During the First World War, the Regiment raised 11 battalions. The 2nd Battalion was virtually annihilated during the Second Battle of Ypres in a poison gas attack launched by the Germans on 24 May 1915. Of the battalion strength of 666 men, just 21 survived.
The 1st Battalion was part of the 86th Brigade of the 29th Division and participated in the landing at V Beach, Cape Helles, on 25 April 1915. The Battalion was among the first to disembark from the SS River Clyde and, together with the Royal Munster Fusiliers, bore the brunt of the Turkish assault: of its original strength of 1012 men, just 375 made it to the shore. Of these, a mere 11 were still alive in December when the decision to evacuate Gallipoli was made.
The 6th (Reserve) and 7th Battalions of the Royal Dublin Fusiliers formed part of the 10th (Irish) Division which landed at Suvla Bay on 6-7 August 1915 and which suffered heavy casualties as a consequence of administrative blunders, lack of maps and a shortage of water and ammunition.
The Regiment was disbanded in 1922 under the terms of the Anglo-Irish Treaty.