The burning of the Custom House, 25 May 1921

Published in Features, Issue 3 (May/June 2021), Volume 29

While it was deemed a propaganda success, could a better plan have yielded an IRA military victory?

By Joseph E.A. Connell Jr

The attack on the Custom House on 25 May 1921 was a resounding propaganda success for the IRA, but from a military point of view there were flaws in the planning and it went against the tenets of guerrilla warfare. Guerrilla warfare is largely one of evasion, and the Irish War of Independence was characterised by the IRA waging a ceaseless and relentless offensive against the weak points of the British—in Dublin and in the countryside—and then withdrawing to attack somewhere else. T.E. Lawrence said that ‘most wars are wars of contact, our war [a guerrilla war] is one of detachment’. A fundamental principle of guerrilla warfare is that no battle or skirmish is to be fought unless it will be won. In his On War (1832), Carl von Clausewitz posited one of the most famous military principles: ‘War is the continuation of politics by other means … the political view is the object … war is the means’. Clausewitz’s and Lawrence’s cardinal rules had as their central tenets:

  • Military action without a clear political objective is useless—and vice versa.
  • A guerrilla war event must include propaganda and politics alongside military action.
  • All events must recognise a military purpose.

As the War of Independence progressed, especially in County Cork, the IRA perfected their guerrilla tactics. In their ambushes they showed a fine knowledge of site choice and deployment. The IRA quickly learned and adopted the classic ambush tactics:

  • Attack with surprise and fury.
  • Do the most damage possible.
  • Fighting only lasts a few minutes—followed by immediate withdrawal.

They became sophisticated enough to attack a barracks as a feint to draw out a relief force and to funnel it into an ambush, while others simultaneously attacked the empty barracks. Alternatively, the IRA would channel British relief forces into ambush sites chosen by the rebels. They became adept at blocking every road in an area except the one leading to their chosen ambush site. The IRA knew that just as important as the planning of the ambush and assault was the planning of the withdrawal.

Dev’s return provided the impetus

In her excellent book May 25: the burning of the Custom House, 1921, Liz Gillis provides the most detailed record of the operation and its participants. When he returned from the United States in December 1921, Eamon de Valera told members of the Dáil that the newspapers in the US were calling the IRA ‘murderers’ because of the way they were conducting the War of Independence:

‘… the odd shooting of a policeman here and there is having a very bad effect, from a propaganda point of view, on us in America. What we want is one good battle about once a month with almost 500 men on each side.’

While there had been plans to attack or burn the Custom House previously, it was de Valera’s return that provided the impetus to proceed. Gillis’s research indicates that there were far more men involved in the attack than had been known previously. The operation was carried out by some 280 Volunteers, five of whom were killed: Tommy Dorrins, Seán Doyle, Dan Head, Capt. Paddy O’Reilly and sixteen-year-old Lt. Stephen O’Reilly (brothers).


Early in 1921 a meeting was held to finalise plans for the taking of the Custom House. De Valera’s first choice was to capture Beggar’s Bush Barracks, but Oscar Traynor, O/C of the Dublin Brigade, deemed that impractical:

‘The meeting proceeded in a very normal way for some time, and then the President [de Valera] spoke, and he made it clear that something in the nature of a big action in Dublin was necessary in order to bring public opinion abroad to bear on the question of Ireland’s case. He felt that such an action in the capital city, which was as well known abroad as London or Paris, would be certain to succeed. He suggested that the capture of the headquarters of the Black and Tans, which was situated in Beggar’s Bush Barracks, would capture the imagination of those he had in mind, apart from the serious blow it would constitute to the enemy.’

BURNING OF THE CUSTOM HOUSE. According to Traynor’s report: ‘Everything went perfectly as per plan, except that just before all the floors had given the Officer Commanding the “OK”, someone blew two blasts on a whistle and all sections retired to the main hall. One officer reported that he had not completed his task of saturation. The Commandant sent him and his men back at once to finish the job. The few minutes’ loss here was the difference between the successful retirement of all the participants and the arrival of large numbers of enemy forces in lorries and armoured cars. These forces swept into Beresford Place at exactly 1.25pm, just five minutes after the time allotted in the plan for the completion of the operation. They were immediately engaged on entry to Beresford Place by the 1st Battalion units with volleys of revolver shots and the throwing of a number of hand-grenades … Everything within the four walls of the Customs House building was reduced to ashes. The fire was still burning ten days after the attack. The fire brigades were unable to go into action for a considerable time. This delay, as well as the use of paraffin oil, played a decisive part in the total destruction of the inside of the building.’ (W.D. Hogan/NLI)

Traynor and others conducted reconnaissance of the Custom House, but it is always vital for those who are to participate in an attack to practise their roles as much as possible. In this case, there was no practice for the participants, and that proved fatal. All military personnel are familiar with German Field Marshal Karl von Molke’s dictum, ‘No battle plan survives contact with the enemy’. In the plans for this operation, the possibility for error was not adequately reckoned and the military purpose seems to have been ignored. As a result, the affair turned into a débâcle for the Dublin IRA. Five of their number were killed and three wounded. Importantly, over 100 were captured—losses the IRA in the city could scarcely afford. The attack sacrificed many experienced Volunteers, and immediate future operations would be degraded by additional and/or prolonged duty for the remaining Volunteers in Dublin. Oscar Traynor noted:

‘Following the action at the Custom House and the capture of a large number of highly trained officers, NCOs and men, it was found necessary to carry out an almost complete re-organisation of the various units of the Dublin Battalion. This, of course, necessitated the appointment of a considerable number of new officers, and naturally while this re-organisation was taking place, actions as we had known them before almost ceased, with the exception of those carried out by the remaining members of the Active Service Unit. As time went on the Brigade units gradually assumed their old aggressiveness, and by the time the Truce was approaching a number of reasonably important operations were being planned.’

Degradation of subsequent operations

In combat, the consequences of degraded performance can be much greater than those in the civil arena. Military members not only have to cope with a hostile environment but also must apply lethal force against a dangerous enemy, maintaining vigilance and exercising good judgement, while ensuring that they protect those in their own unit. If a unit suffers casualties that reduce its numbers, its performance will be degraded. Prolonged or continuous deployments or missions cannot be sustained. While the members of the Dublin Brigade were able to continue harassing and attacking the British, they were fortunate that the Truce of 11 July ended military operations quickly after the raid.

In the meeting discussing the operation, de Valera countered objections, saying that ‘if 120 men were lost and the job accomplished, the sacrifice would be well justified’. In fact, over 100 Volunteers were arrested after the attack. To lose approximately 40% of the attacking force as casualties was a devastating blow to the Dublin IRA. One of Che Guevara’s tenets for any guerrilla action was that ‘the man must survive the plan’.

Alternative scenario

I believe, however, that the attack could have achieved Lawrence’s, Clausewitz’s and Guevara’s triple objectives in a way that was being used by the Volunteers in their attacks throughout Ireland. It is axiomatic to distract and then flank the enemy with multiple coordinated attacks. In the countryside, the IRA commonly used some event to draw the British out of their barracks and lead them into a planned ambush, resulting in the capture of weapons and neutralisation of the British forces. Those tactics, techniques and procedures should have been adapted to this Dublin event to maximise damage to the British and minimise losses to the IRA.

I believe that the Dublin command should have initiated an attack on Amiens Street railway station (now Connolly Station), only a few hundred metres from the Custom House, as a reconnaissance mission. Such a feint could have been done about three weeks before the planned Custom House attack, and the much smaller number of Volunteers involved would have faded into the north Dublin inner-city warren of streets to escape. No attempt to hamper communications or the Fire Brigade response should have been undertaken. The British would immediately have responded with troops, Black and Tans and Auxiliaries from several Dublin barracks. IRA spotters on the quays could have timed the response of troops from Royal Barracks (now Collins Barracks) and determined an interception point on the Quays. Likewise, British responders from Portobello Barracks (now Cathal Brugha Barracks) could have been spotted on Aungier Street, those from Beggar’s Bush Barracks spotted on Mount Street, and other units responding could have been observed and timed for the most advantageous interception points for interdiction.

On 25 May 1921, the Custom House attack would have proceeded as planned, but with only half of the Volunteers assigned to fire the building. Those in the Custom House would utilise the lessons they had learned in the firing of Amiens Street station just a few weeks before. The other half of the Volunteers would be split up into ambush parties and multiple ambushes planned at all the interception points of the military responders, coordinated to begin after the fires were set and at such time as to make the ambushes concurrent. Following the ambushes, the Volunteers would utilise the ‘hit and run’ tactics they had perfected in Dublin and throughout the country, and immediately withdraw to the safety of Dublin’s backstreets. Further, this time the Volunteers would take the same actions they employed to neutralise the response of the Dublin Fire Brigade, including taking over the Central Station on Tara Street.

Just as the simultaneous and coordinated attacks on Bloody Sunday threw the British intelligence forces into panic, so, too, such synchronised ambushes would have sent the word throughout the British military forces that whenever they responded in Dublin they could be heading into an ambush. Any guerrilla army must create fear in the enemy; the British always had to be aware that an attack could be imminent. As repeated so many times in the War of Independence, an attack’s purpose was not just to eliminate the British troops but also to make sure that a message was sent to the British. The Custom House fire was successful for its propaganda value, but it was a heavy blow in terms of the numbers lost, both killed and arrested. A better plan could have lessened, if not avoided, those losses, and provided the IRA with a military victory as well.

Joseph E.A. Connell Jr is the author of The shadow war: Michael Collins and the politics of violence (Eastwood Books).



L. Gillis, May 25: the burning of the Custom House, 1921 (Dublin, 2017).

O. Traynor, ‘The burning of the Custom House’, in Dublin’s fighting story (Tralee, 1939).


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