Bureau of Military History (1913-1921)The Bureau of Military History Collection, 1913-1921 (BMH) is a collection of 1,773 witness statements; 334 sets of contemporary documents; 42 sets of photographs and 13 voice recordings that were collected by the State between 1947 and 1957, in order to gather primary source material for the revolutionary period in Ireland from 1913 to 1921.