A rare and previously unknown IRA intelligence dossier from the War of Independence has emerged as part of a new permanent exhibition covering the Wars of Independence and the Civil War.
The book, which contains photos and details of British forces at Dublin Castle and elsewhere, was compiled to identify and target many of them.
It has been loaned to the National Museum at Collins Barracks in Dublin by Gerard Fitzpatrick, from Clones, Co Monaghan, whose father was an intelligence officer in the Irish Army.
He is uncertain, however, as to how his father came into possession of the book.
The book contains photos, which were often obtained from photographic studios in Dublin and from spies within Dublin Castle, and details names, ranks and other details, such as nicknames.
In some cases. men are described in detail. "Of a nervous disposition" is one observation and "torturer" is another.
It is known that some of the men in the photographs were later killed by the IRA.
Mr Fitzpatrick said he had only realised the importance of the ledger when he contacted the National Museum.
"I was amazed at what they were able to tell me about its importance," he said. He urged others with artifacts from the 1919 to 1923 period to contact the museum.
The curator of the exhibition, Brenda Malone, said the book is a unique asset of the history of the period.
She described it as an important glimpse into the intelligence-gathering capabilities of the IRA at the time of the War of Independence.