9 January – the Lillebonne, the largest vessel ever constructed in Dublin, is successfully launched in the North Wall Yard.
16 February – at the Royal Navy's Haulbowline base, explosions on board the newly-commissioned submarine HMS A5 due to petrol fumes after refuelling kill six of the eleven crew.
6 March – the obligation of the Post Office in regard to letters addressed in Irish is raised in the British House of Commons. The debate arises because the GPO in Dublin returned parcels addressed in Irish by the Gaelic League.
29 May – statistics for Ireland in 1904 show that nearly 37,000 people emigrated. Since 1851 almost 4 million people have left the island.