But it is more likely that the content of the‘Castle Document was a composite of material secreted out from inside the British administration, and of the creative writing, probably, of James Plunkett.

The document suggested military raids were planned, at an imminent unknown date, in which arrests would be made of the officers of the Irish Volunteers, National Volunteers, and Gaelic League.

From a military perspective, the naming of certain addresses to be taken over meant the Volunteers and James Connolly’s Irish Citizen Army were effectively being suppressed after months of police surveillance of their leaders’ every move. Those premises included Citizen Army and ITGWU headquarters at Liberty Hall, Irish Volunteers HQ at Dawson St, and other premises regularly named in daily ‘movement of extremists’ reports from Dublin police detectives.

Furthermore, communication was to be restricted in and out of the homes of Plunkett, Irish Volunteers chief of staff Eoin MacNeill, Constance Markievicz, and Padraig Pearse’s St Enda’s College, among other locations.

The document was distributed to newspapers over the weekend of Saturday and Sunday, 15 and 16, Palm Sunday, 1916 — but there was little take-up by editors, probably under fear of wartime censorship.

It was not until a copy found its way into the hands of Dublin Corporation member Tom Kelly, and he read it to the council on Wednesday, April 19, that it eventually became public.

The reaction was mixed: Many people, on reading reports of the document, believed Dublin Castle’s claims that it was bogus (a focus on Dublin City only instead of the whole country, and highlighting printing anomalies helped bolster the argument).

But the senior IRB men managed to convince MacNeill of the need to place regional and local commanders around the country on notice to defend their arms with force if necessary.

He had been unaware of the secret plans to launch a rebellion on Easter Sunday. But it was his willingness to back the Rising in light of this information — and on finally learning of the planned Rising on Good Friday, April 21, 1916 — that led to the confused orders emanating from Irish Volunteers headquarters in the lead up to Easter weekend.

In Cork, for example, Brigade commandant Tomás MacCurtain received no fewer than nine messages from Dublin — some from Seán MacDiarmada and Padraig Pearse of the IRB military council — up to Easter Monday.

The news that reached Dublin on Saturday — of the Aud and its cargo of guns from Germany being arrested and sunk off the south-west coast — had eventually convinced him to issue the infamous countermanding orders. By despatches around the country and a notice placed in the Easter Sunday edition of the Sunday Independent, he effectively ensured a far lower turnout than might otherwise have been expected of Irish Volunteers for the rebellion that was to have kicked off that evening.

The Rising did, however, eventually begin— almost 24 hours later than planned — on Easter Monday, April 24, 1916.

Bill McCormack’s forensic analysis of whether — or to what extent — the Castle Document was a forgery is in Making 1916 — Material and Visual Culture of the Easter Rising, edited by Lisa Godson & Joanna Bruck (Liverpool University Press, 2015).