Intelligence in the Irish War of Independence

By: Olivia Jackson 

In the Early 20th century Ireland sought independence from Great Britain, as they were

unsatisfied with British rule. Ireland did not feel adequately represented by Great Britain and had

been denied independence several times before, including the failed Easter Rising of 1916. The

typically Catholic Irish wanted greater separation from the Protestant British, and the partial

independence of Home Rule was falling short. These tensions lead to the formation of the Irish

Republican Army (IRA) and the War of Independence, also known as the Anglo-Irish War,

which lasted from 1919 to 1921. A truce was agreed to on July 11, 1921 and a treaty was

finalized and ratified on December 5 of the same year. The southern 26 counties became the Irish

Free State - later to become the Republic of Ireland, with the remaining six northern counties

staying a part of the United Kingdom as Northern Ireland. This agreement did not fully end the

tensions within Ireland, which soon erupted into a civil war. The Irish Civil War was relatively

short, only spanning from 1922-1923, but involved fighting between the Provisional

Government, those who supported the treaty and the IRA, those opposed to the treaty. Only

enemies a year prior, the Provisional Government began sharing intelligence with Britain to

maintain control during the Irish Civil War. Despite this newfound cooperation, relations

remained tense for some time.


During the War of Independence, there were clear directives that either side fought to

achieve. From the Irish perspective, every decision made by the IRA leadership came down to

the end goal of gaining independence from the British and forming their own republic free of the

empire. The British sought to quell the violence and stop the uprising to hold onto their territory.

As the nature of the war kept evolving, each side had to assess how best to use the intelligence

they had gathered to effectively cripple the other side.


The Anglo-Irish War had four phases and the military intelligence capabilities of each

side seemed to dictate who had the upper hand. The first phase shows the destruction of the

Dublin Castle intelligence system and the IRA taking the advantage. In the second phase, the tide

shifts and the British begin to play a leading role. However, the third phase shows the British

excelling at overt intelligence collection, but a wave of ruthless executions of informants by the

IRA. In the fourth phase, the IRA dominated covert intelligence collection and won overall.


While the number of troops and quality of military strategy was important, “the War of

Independence was largely an intelligence war.” (26) An IRA leader, Micheal Collins, was able to

gain access to the British intelligence G Division’s document room and examine their files. The

IRA used this information “collected from these sources to go on the offensive” (28) and

successfully launched attacks against the Dublin Metropolitan Police (DMP) and the Royal Irish

Constabulary’s (RIC) Crime Special Branch. The IRA’s continued achievements in covert

operations lead to great successes and eventual winning of the war overall. The British also were

able to use their intelligence to make better strategic moves, although ultimately with less

success. One of the most useful sources of intelligence for the British came from captured Irish

documents. Raids on IRA houses “gave the crown a good picture of the organization and

personnel of their opponents.” (46) Weak IRA operational security gave British intelligence

officers accurate information on who to target and led to many fruitful operations due to the high

volume of valuable information gathered. IRA members often failed to destroy sensitive

materials that the British could easily gain access to, and members would regularly take sensitive

and covert materials home, where the British would gather them during raids. British intelligence

officers were also able to use outside alliances as sources of information; “America was

sometimes the best source of information on republican plots back in Ireland.” (111) Using these

foreign ties, the British were able to make better informed military decisions during the war,

such as who to target, where to attack, and accounting for when the IRA was planning their own

attacks. Both the IRA and the British used intelligence gained through covert or overt means to

more effectively plan and strategize attacks to further their goals.


High quality intelligence often leads to effective decision-making. However, good

intelligence was not always abundant and failures within the intelligence cycle led to greater

mistakes in the decision-making process. Failures during the collection process mainly occurred

from the British side, which ultimately led to their defeat and loss of the territory. The British

intelligence system was then in its nascent stages and dealt with a lot of weakness. Issues

stemmed from the planning stage of the intelligence cycle as the system was afflicted with

“inexperienced officers, amateur techniques, poor security, lack of co-ordination.” (49) Britain’s

policies also influenced their intelligence cycle and decision-making. Since their “constitutional

and security policy towards Ireland was always one step behind the developing political

situation,” the intelligence system suffered the same way (50). Decision-makers struggled mainly

during the processing and analysis steps of the intelligence cycles because they allowed their

political views and biases to color the information collected. Too often “signals [were] missed,

good intelligence [was] not distinguished from bad information, policy-makers [saw] what they

[wanted] to see.” (51) Biased analysis or collecting only the information that suited their

preconceived notions instead of all information available can lead to mission failures. One such

example was when British intelligence officers ordered an attack on IRA headquarters “on the basis of a single secret intelligence report.” (78) This was truly a failure in planning, collection,

processing, and analysis. The report was unable to be confirmed and the army refused to obey

the order.


The IRA ran such an effective counterintelligence campaign that the British forces had

little actionable covert intelligence, and the British were largely incapable of recruiting agents or

placing their own within IRA ranks. By the end of 1919 “the IRA had been successful in

‘putting out the eyes of the British’” due to their aggressive covert operations (29). This was

essential in their decision-making process as it allowed the Irish to control the narrative of what

the British did and did not know. The IRA information allowed their agents to respond

immediately and effectively when the British attempted to improve their intelligence.

The IRA and the British possessed different strengths and weaknesses in intelligence

capabilities. In general, the IRA excelled at covert operations while the British led in overt

intelligence collections. Throughout the entire period of the war, “the IRA had the upper hand in

the covert struggle” (26) and was able to use this supremacy to thwart British operations

consistently. Through the vast successes in covert operations, the IRA essentially destroyed the

intelligence capacity of the Irish police and Dublin Castle. In general, “Irish revolutionaries paid

more attention to security and waged a more effective counter-intelligence campaign.” (47) They

held this advantage during the entire war, while the British only began to develop their

intelligence services part of the way through.


Where the British struggled in covert collections, they made up for these losses in their

overt collection capabilities. These gains were somewhat diminished by poor handling of said

intelligence. Record-keeping during this time was severely lacking, so when a member of the

DMP “was killed or quit the force, he often took with him all the intelligence that had been built up.” (28) Such lapses in security set back their capabilities, as well as staffing issues since much

of the military intelligence system relied on junior officers. Yet, from the second phase of the

war and on, the British began to bolster their efforts and gain traction through overt means. The

brunt of the overt intelligence came from documents captured in raids, or information from

prisoners and defectors. By April of 1921, it was estimated that “80 per cent of all British

intelligence was a by-product of overt security measures.” (46) Unfortunately for the British,

their reliance on unobtrusive and unaggressive collection methods resulted in failures to

penetrate IRA circles. After the truce was agreed to, “the flow of intelligence largely dried up.”

(57) While overt intelligence collection is useful for information, it is not necessarily harmful to

the mission of the opposition. With the intense use of covert intelligence from the IRA, they

were able to collect information against the British and effectively blind them to their own

operations in the beginning of the war.


The British made several critical intelligence mistakes that led to their ultimate failure to

hold Ireland within the United Kingdom. From the start of the conflict, the British intelligence

system struggled with information sharing between the different organizations, and a general

lack of understanding and awareness of their adversaries. Initially, the quality of their

intelligence was “stymied by the inability or unwillingness of British intelligence chiefs to use it

properly” and their general reluctance to share intelligence with Dublin Castle (20). This slow

start to the intelligence battle continued to cripple their efforts throughout the crisis. Perhaps the

biggest intelligence failure throughout the entire conflict was the previously mentioned

attempted attack on IRA headquarters. The British army outright refused to follow the order, and

“cast doubt on the value of the intelligence supplied.” (79) Losing the confidence and loyalty of

troops is a clear mission failure and difficult to recover from. Completely failing to understand

the Irish culture, undercover British officers “automatically aroused suspicion, especially in rural

areas.” (47) Along these same lines, the British were wholly unable to recruit or neutralize Irish

radicals. A greater understanding of the culture would have informed the passion with which the

IRA fought and enabled the British to update their strategies accordingly. The British

intelligence services failed in the basic tenet of war: know thy enemy.


Along with the lack of cultural understanding, another source of British defeat stems

from a strong bias against the Irish. Initially before the war started, British leadership could not

recognize the growing dissent as a popular and indigenous movement, which was part of an

“overall failure to understand the political situation in Ireland and the likely implications of

British policies.” (24) The British did not see the Irish as a threat to take seriously, and filled in

gaps in knowledge with “worst-case, often politically motivated, interpretation” and sometimes

even gossip (58). There was a persistent belief that revolutionary violence “was not due to

political opposition to British Rule but was instead caused by a genetic disposition to ‘blood

lust.’” (172) By blaming Irish actions on prejudiced beliefs instead of as a genuine response to

unfair British rule, they failed to take their adversary as seriously as they should have and

ultimately lost the war against them. Had the British been more honest and aware about who they

were fighting, they may have had more success in developing intelligence strategies and may

have been able to retain more than just the north 6 Irish counties. The British were also

unprepared for different outcomes in the brief period between the truce and the treaty.

Immediately after the truce was agreed to, the British experienced a “dramatic reduction in

[their] intelligence capabilities” while the IRA used the peacetime to bolster their army in case

the treaty did not pass, and the fighting resumed. Ultimately, the British lost because they did not

take the threat of the Irish seriously due to biases and cultural misunderstandings, they only successfully employed overt operations rather than covert, and could not penetrate the Irish