Britain won the 1916 battle, but its crackdown eventually lost the war
Herbert Henry Asquith first heard that a rebellion had broken out in Dublin on the evening of Easter Monday.
According to one eye-witness in 10 Downing Street, the British Prime Minister did not seem particularly concerned.
He simply remarked, "Well, that's something" - and went off to bed.
Asquith's indifference was an early sign that the British had no real idea of how to handle the Easter Rising. Fatally distracted by the war in Europe, Asquith's government made a series of political blunders that swung Irish public opinion firmly behind the rebels.
As a result, their military victory soon turned into moral defeat - and Ireland's independence became only a matter of time.
For a start, Britain could very easily have strangled the Rising at birth. By April 1916 they had broken Germany's naval radio codes and were well aware of Roger Casement's mission to import arms.
Dublin Castle had spies in the Volunteers, who reported that the IRB's Thomas MacDonagh told his troops, "We are going out on Sunday, boys, and some of us may never come back."
Even then, however, Chief Secretary Augustine Birrell failed to act. He was a well-meaning but lazy man, more or less ignored by his political masters in London.
Ireland had been a huge issue in British politics immediately before 1914, but the outbreak of World War I changed all that. Birrell later complained that when he attended cabinet meetings, "A jackdaw or a magpie could do just as well by crying out 'Ireland, Ireland, Ireland!' at intervals in the proceedings."
After Roger Casement was arrested in Kerry on April 21, Birrell and his colleagues assumed that the danger was over. When the Rising started three days later, there were fewer than 400 British soldiers in Dublin because most had gone to the races at Fairyhouse.
Dublin Castle was almost empty and the rebels could probably have seized it if they had made a serious effort.
The eventual British military response was efficient, crushing the Rising within six days. The political response, however, was much less impressive.
Asquith imposed martial law and handed control of the situation over to Major-General Sir John Maxwell (inset), a dour Scottish Presbyterian with very little knowledge of Ireland.
As soon as he arrived in Dublin, Maxwell declared that he intended to show "no mercy". In practice, this meant executing the rebel leaders as soon as possible after secret court-martial trials in Richmond Barracks.
The accused were not allowed to have defence counsels and inevitably some travesties of justice took place. To take just one example, Patrick Pearse's younger brother Willie was a minor player in the Rising but seems to have been shot purely because of his surname.
Maxwell also ordered a crackdown on all known Sinn Fein supporters in the country. Unfortunately, Dublin Castle's files were out of date and around half of the 3,500 people arrested turned out to be completely harmless. They were released almost immediately - but the bitter legacy created by this heavy-handed treatment lingered on for much longer.
Other reports of British brutality gradually began to leak out. The GPO survivors had been taken to a garden in the Rotunda Hospital, where soldiers mocked the elderly Tom Clarke and stripped him naked in front of nurses watching from the windows.
Francis Sheehy-Skeffington, a well-known eccentric and pacifist, had been arrested and shot by a half-crazed army captain with no idea of who he was.
Within weeks of the Rising, there were reports of young girls praying to 'St Pearse'. According to one British journalist, Irish people read about the executions with the "helpless rage" of someone watching "a stream of blood dripping from under a closed door".
Even a middle-class Protestant such as WB Yeats's sister Lily was fuming, stating: "We [Ireland and England] can never understand each other."
Maxwell himself was bewildered by the public reaction. "Some of the Irish call me very nasty names, Bloody Butcher and such like, but my skin is thick," he wrote to his wife in July. Later he declared, "Oh! These Irish are a truly wonderful people. It is difficult to take them seriously; they are likened to spoiled children."
A 2006 RTE documentary about Maxwell was called The Man Who Lost Ireland. While there is some truth in this, the real blame lies with senior British politicians whose ignorance of Ireland meant that they failed to realise just how much damage he was doing.
Shortly before Patrick Pearse faced the firing squad he wrote to his mother: "People will say hard things of us now, but later on they will praise us."
He was right - not least because the British played such a crucial part in their own downfall.