However, this policy was reversed after a meeting of the Ministry of Dáil Éireann in May 1921 where the President of the Republic, Éamon de Valera, called for a spectacular public show of force by the IRA, to reinforce the idea that it was an army representing an Irish government.

For this reason it was decided to attack and burn the Custom House, which, although an important government building, was not defended by the British military.

[6] Michael O'Kelly, Lieutenant E Company, 2nd Battalion, Dublin Brigade, recalled plans to "deliver a smashing blow to England".

Two large scale operations - to capture Beggars Bush Barracks, or to destroy the Customs House were initially considered.

[7] IRA member Vincent Byrne said that the operation was "one of many under review" and that another proposal had been to attack Beggars Bush Barracks.

[8] In the early afternoon of 25 May 1921, roughly 120 non-uniformed IRA Volunteers began to gather around the Custom House in groups of twos and threes.

[2][10] However, at about 1.10pm, a watching policeman notified British forces and 60 Auxiliaries in three lorries and an armored car quickly arrived on the scene.

[12] British military forces composed of units from the Wiltshire Regiment arrived and took over the operation from the Auxiliaries at this point.

The Custom House was the seat of an alien tyranny.From the republican point of view, the operation was successful for its propaganda value, but it was a heavy blow in terms of the numbers lost, both killed and arrested.

[15] The armed conflict was brought to an end on 11 July 1921 and negotiations were opened which would produce the Anglo-Irish Treaty in December of that year.

Irish local government records from the 1600s had been brought from rural parts of Ireland to the Custom House for safekeeping, and these were lost in the blaze.