The Bureau was originally set up in 1947 to compile 'the history of the movement for Independence from the formation of the Irish Volunteers on 25th November 1913, to the 11th July 1921'. It comprises of '1773 witness statements, 334 sets of contemporary documents, 42 individual photograph collections, 210 photographs of action sites during Easter Week taken subsequently by the Air Corps, 12 voice recordings, and a collection of press cuttings were assembled by the Bureau' put together over eleven years. All this information is now available online for free at the newly launched Bureau of Military History website.
Here you can search '36,000 pages of witness statements' , search the PDF index of witnesses, search the PDF of relevant press cuttings from the period and view their categorised image gallery and listen to audio files. The website states that ' the Bureau is among the most important primary sources of information on this period available anywhere in the world.'