The daring capture of a British naval ship that enraged Downing Street and armed anti-Treaty IRA for Civil War

As the British naval ship Upnor steamed out of Cork harbour just after midday on March 29, 1922, little did its captain and crew know that it would play a prominent part in one of the most dramatic events of the Anglo-Irish conflict.

After clearing the headland beyond Roches Point, a south-easterly course was set toward Land’s End in England, followed by a short run up the English Channel to Devonport Naval Dockyard, where it was to deposit its cargo of arms, ammunition and navy stores.

Such voyages were routine in early 1922 as the British government evacuated its troops and equipment back to England following the ratification of the Anglo-Irish Treaty by Dáil Éireann on January 7 of that year.

As Ireland teetered on the brink of civil war, with the IRA divided into pro- and anti-Treaty factions, the early months of 1922 saw Crown forces vacating barracks and military installations across Ireland. In an increasingly unstable political environment, both IRA factions immediately competed with one another to occupy the vacated garrisons and assert their authority. Possessing sufficient arms and ammunition was vital in the quest for such control.

In Cork, faced with a dwindling arms supply, the anti-Treaty IRA leader Sean O’Hegarty was determined to arm his units and ensure that Cork and the greater Munster region would not fall into the hands of his pro-Treaty enemies. ​

O’Hegarty (41), a teetotaller and strict disciplinarian, was one of the most successful IRA leaders during the War of Independence. Alongside fellow IRA leader Tom Barry, his Cork Number 1 Brigade drove the British out of much of the Cork countryside and made Cork city virtually ungovernable.

In late March 1922, O’Hegarty received information from his IRA intelligence network within the Royal Navy’s dockyard at Haulbowline in Cobh. The dispatch confirmed that the Upnor would be transporting a large consignment of arms, ammunition and explosives to England on March 29.

A direct raid on the heavily fortified dockyard was immediately ruled out because of the strong British military presence in the area. However, an alternative audacious plan was conceived by O’Hegarty and his staff officers, among them his deputy Mick Leahy. Leahy, a 25-year-old marine engineer, was trained by the Royal Navy at Haulbowline. He had extensive contacts and knowledge of the workings of the naval base.

When word of the Upnor’s departure was confirmed to Leahy on the morning of March 29, O’Hegarty and his men quickly set their plan in motion to seize the arms shipment. Their first step involved kidnapping Jeremiah Collins – an IRA sympathiser and former ship’s captain – and taking him to the port of Cobh.

When O’Hegarty received the signal just after midnight that the ships had docked, he led the convoy of lorries down to the pier

The IRA had already seized a tugboat, the Warrior, owned by the London-based Elliott Steam Company. With Collins as captain, they sped off out of Cobh in pursuit of the arms ship.

Later that evening, they intercepted the Upnor 35 miles beyond Roches Point. Flying a stolen British admiralty flag on the Warrior, Collins pretended they were carrying an important message for the ship’s captain (the Upnor had no working wireless). The captain cut the ship’s engines, allowing the IRA to storm the Upnor and install their own crew. Both ships then set sail for the fishing port of Ballycotton.

Meanwhile, back on land, the IRA had hijacked over 80 lorries and cars across Cork city and drove them to Ballycotton. Trees were felled on all the main roads in the surrounding area of the village to prevent outside interference and the arrival of enemy forces.

When O’Hegarty received the signal just after midnight that the ships had docked, he led the convoy of lorries down to the pier. Working through the night and into the early morning, almost 1,000 men, IRA members and locals, unloaded the ship’s cargo of machine guns, rifles, revolvers, ammunition and explosives.

At 10.30am on March 30, two British destroyers, HMS Heather and HMS Strenuous, were sighted outside Ballycotton Bay before the unloading had been completed. O’Hegarty made the decision to immediately withdraw, abandoning the small amount of arms remaining on the ship. On leaving Ballycotton, the convoy proceeded to a range of destinations through a series of pre-planned routes where the 120-tonne haul was dispersed to secret arms dumps throughout Cork and across Munster.

Tom Mahon, author of The Ballycotton Job, stated that the incident caused an "almighty uproar in London and Dublin". General Nevil Macready, the outgoing commander of British forces in Ireland, declared that the British government reacted with a greater degree of "wild excitement" than had occurred after the outbreak of World War I in 1914.

Mahon claimed that "the capture of the Upnor had significant political and military consequences as it forced the British to start arming Collins’ National Army

As a furious Michael Collins accused the British of colluding to arm his opponents in the anti-Treaty IRA, Winston Churchill admitted that "the Irish have a genius for conspiracy".

Never in the history of the British empire had one of her ships been captured in such a well-conceived operation. The Irish Independent called it "an amazing exploit" and the London Times referred to it as a "clever and daring coup". Across the Atlantic, the New York Times remarked that it was a "sensational affair... carried out with great audacity".

Mahon claimed that "the capture of the Upnor had significant political and military consequences as it forced the British to start arming Collins’ National Army in the face of an increasingly well-armed anti-Treaty side", both of which led further down the road to an inevitable civil war.

O’Hegarty never took part in that war, resigning as commander of the anti-Treaty IRA in Cork in June 1922, on the eve of the outbreak of hostilities.

Playing a leading role in the ultimately futile negotiations to find peace between both sides, he met Collins in Cork on August 21, 1922, the day before Collins was shot dead in an ambush at Béal na Bláth.

Considering that the vast majority of the Cork anti-Treaty IRA’s arms and ammunition came from the Upnor, there is a strong possibility that the bullet that killed Collins came from the daring operation that O’Hegarty masterminded.

Dr Patrick McGarty is Senior Lecturer in Public Policy at Munster Technological University