The Irish Volunteers had been infiltrated by the Irish Republican Brotherhood, which planned on using the organisation to stage an armed rebellion, with the goal of separating Ireland from the United Kingdom and establishing an Irish Republic. The entry of the UK into the First World War was, in their view, a perfect opportunity to do that. With the co-operation of James Connolly and the Irish Citizen Army, a secret council of IRB officials planned a general rising at Easter 1916. On the Wednesday before Easter, they presented MacNeill with a letter, allegedly stolen from high-ranking British staff in Dublin Castle, indicating that the British were going to arrest him and all the other nationalist leaders. Unbeknownst to MacNeill, the letter—called the Castle Document—was a forgery.