David O’Callaghan was born in Western Australia on 17 June 1960. He enlisted in the Army on 31 January 1978 and was allocated to the Royal Australian Infantry. He underwent SAS selection in 1980 and was posted to SASR on 17 October 1980. David came from 6th Battalion Royal Australian Regiment with the rank of Private on posting to SASR.

April 16, 1982