Five days before the Rising the Evening Mail carried a story that would have a bearing on the course of events and create a controversy which still burns. Addressing a meeting of Dublin Corporation, Thomas Kelly of Sinn Féin read into the record the text of a secret document he had been given. 

Known as the Castle Document, it contained details of contingency plans for Martial Law, and the arrest and detention of the leaders of Sinn Féin, the National and Irish Volunteers, and the Gaelic League. It also included a list of buildings to be secured by the military. 

Questions remain about its provenance: Did such a plan exist at all? Was a military plan invented to propel momentum toward an uprising? And by who? Was an existing plan altered or doctored to enhance the possibility of a rising, which the Volunteers had deemed necessary before the First World War ended? 

Eoin MacNeill, the Volunteers’ chief of staff, said that the “document served the purpose of creating great excitement and apprehension of the Volunteers being suppressed – an event which we were all bound to resist”. 

He wrote: “There was intense tension during these meetings [of the leadership]. At the exec[utive] there was some proposal for a general order which I opposed as being dangerous, and ultimately at the end of the meeting a different general order was drafted by me and accepted by Pearse as satisfactory. It ordered the Volunteers to prepare themselves against suppression”. 

MacNeill then changed his mind about the authenticity of the Castle Document: “…a fact came to my knowledge showing me that I had been deceived”. 

The identity of the official who leaked the document was revealed in 1971 through a letter in the Irish Press. The writer, Patrick J Little, whose papers are in the UCD archives, revealed that it was “the late Eugene Smyth, a telegraphist”, who “had the opportunity of obtaining full and direct information of the substance of the plans contained in the document”. 

The letter contained a solemn statement from Smyth which included: “I can definitely confirm the truth of the contents of the document”. In 1951 Smyth gave a witness statement to the Bureau of Military History: “The contents of the document were practically identical with that read out by Alderman Tom Kelly at the meeting of the Corporation…”