Brennan, Michael (1896–1986), revolutionary and army chief of staff, was born 2 February 1896 in Meelick, Co. Clare, third son of Patrick Brennan, farmer, and Mary Brennan (née Clancy). Educated at St Munchin's College, Limerick, aged 15 he joined Fianna Éireann and was sworn into the IRB, joining his brothers Paddy (b. 1892) and Austin (qv). In November 1913 he helped found a branch of the Irish Volunteers in Limerick and sat on its provisional committee. Early in 1914, after he moved to Dublin to study wireless telegraphy to become a ship's radio operator, he contacted Seán Mac Diarmada (qv), who introduced him to IRB leaders. In summer 1914 Mac Diarmada advised him to return home to work as an organising and training officer: he spent the next eighteen months cycling throughout Clare and Limerick, training Volunteer companies. Early in 1916 he was arrested after publicly urging Volunteers to shoot anyone who attempted to seize their arms. Sentenced to three months in Limerick jail, he was released on appeal and began to prepare for the Easter rising. Given vague orders to cut the roads from Clare to Limerick, he dutifully turned out with his small, poorly armed band but, demoralised after an uneventful rain-soaked weekend, they voted to disperse. Brennan later noted wryly that his men were rather more prepared to die for Ireland than to get wet for it. He then marched on Limerick with a few men but was arrested. Imprisoned in Richmond barracks, Wakefield, Frongoch, and Reading, he was released in December 1916.
Believing the IRB preferred conspiracy to combat, after 1916 he helped push its old guard aside and was elected North Munster member on the IRB supreme council. Rearrested for organising Volunteers in February 1917, he was detained at Arbour Hill and confined to private lodgings at Wetherby, Yorkshire, escaping in May 1917. He returned to Clare and was asked to stand as Sinn Féin candidate in the by-election of July 1917; he declined in favour of Éamon de Valera (qv) and acted as a member of his bodyguard during the campaign. Soon afterwards he was appointed brigade adjutant in Clare; his brother Paddy was appointed brigadier. Without consulting Dublin, the Brennans developed a strategy of provoking the authorities into arresting Volunteers, who would then refuse to recognise British courts and hunger-strike for political status. After the election the three Brennans were arrested for illegal drilling and put their plan into operation. Sentenced to two years hard labour (12 July 1917), they were imprisoned in Cork and then Mountjoy, where they went on hunger strike until political status was granted on 20 September 1917. Michael was moved to Dundalk in November and after a brief hunger strike was released under the ‘cat and mouse’ act. Rearrested 26 February 1918, he was held at Dundalk and Belfast, where he was elected prison commandant.
Released 24 December 1918, he assumed command of the East Clare brigade. The original Clare brigade had been wracked by in-fighting among the Brennan, Barrett, and O'Donnell families, and in late 1918 GHQ divided the county into three brigades, allocating one to each family. The Brennans were unhappy with this arrangement, having sought command of a division controlling all three brigades, and Paddy resigned; he later became clerk to the Limerick board of guardians and Sinn Féin TD for Co. Clare (1921–3). Although Michael Brennan's belligerence frequently brought him into conflict with headquarters, which was anxious to avoid precipitate open conflict, he continued to force the pace and his brigade's attacks on police huts in Clare (July–August 1919) effectively began the sustained guerrilla war. Frustrated at not being sent arms from GHQ, in December 1919 he ordered the seizure of old-age-pension money from Limerick post office for funds to buy arms. This led GHQ to replace him temporarily as commandant with his brother Austin. During 1920 all three Brennan brothers were on the run, and the family home in Meelick was burnt to the ground as a reprisal.
From mid 1920, in a spontaneous rather than planned development, Brennan banded together with on-the-run comrades to form a flying column. Under his aggressive leadership it became a highly effective thirty-strong unit. It guarded the captured Gen. Lucas in July 1920 and took part in major actions at Kilmallock, Co. Limerick (20 May 1920), and in Clare at O'Brien's Bridge (29 September 1920) (where Brennan was badly wounded in the arm), Glenwood (20 January 1921), and Kilrush (24 April 1921); Brennan also saw action in Dublin on his visits there. In May 1921 he was appointed commander of the 1st Western Division, which combined the Clare and south Galway brigades.
Elected chairman of the Sinn-Féin-dominated Clare county council in June 1920, he gave priority to military matters and continued to destroy communications. However, he managed to maintain a reasonable level of civic services, and won the respect of labour leaders and even some unionist opponents. Alive to the propaganda side of the conflict, he used ‘cattle drives’ to recruit Volunteers and insisted his men behave with civility to non-combatants and pay for any goods taken.
He was the only commander of a western or southern division to accept the treaty – though very much as a means to achieving a republic. Ordered in early July 1922 to take Limerick, the strategically crucial pivot of anti-treaty units in the south and west, his poorly equipped division (most of his men lacked even rifles) had no prospect of dislodging the occupying anti-treatyites. He bought time by negotiating a truce with Liam Lynch (qv) (which caused some of Brennan's superiors to doubt his loyalty), until arms and reinforcements arrived from Dublin. On 11 July Brennan attacked and, in one of the war's decisive actions, took the city on 20 July after fierce fighting. He followed up by defeating anti-treaty forces in Clare, and was appointed GOC Limerick Command (23 January 1923).
He was appointed GOC Southern Command 29 February 1924, adjutant-general 15 October 1925, inspector-general October 1928, and army chief of staff 15 October 1931. When Fianna Fáil came to power in 1932 he firmly resisted suggestions from the garda commissioner, Eoin O'Duffy (qv), that the army should refuse to cooperate with the new government; he quietly transferred suspect officers from key positions and made it clear he would support any democratically elected government. His war record and republicanism made him an acceptable chief of staff to a Fianna Fáil government, and he served three three-year terms (most of his predecessors had resigned or been forced out after a term or less). His tenure as chief of staff was difficult: by the early 1930s the army had fallen to only 6,000 men, dispersed in small units and chronically under-equipped. As war in Europe loomed Brennan forcibly pointed out to the government the inadequacy of Ireland's defences, but his calls for extra resources fell on deaf ears. After the Magazine Fort in the Phoenix Park was raided by the IRA (23 December 1939) and most of the army's ammunition reserves stolen, he was replaced as chief of staff by Dan McKenna (qv) in January 1940. Many people connected the two events, but the decision to replace him had been taken weeks before the raid and he won £500 in a libel action in May 1940 against the Daily Telegraph for suggesting otherwise. He was offered but refused a subordinate command, and retired from the army as lieutenant-general to become a chief superintendent in the OPW until 1961.
He married Bridget Conheady; they had one son and two daughters, and resided at South Hill, Killiney, Co. Dublin. He died 24 October 1986 in Dublin, and was buried at Deansgrange cemetery.