An Irish-born explorer and British Army officer, he is best known for his influential books on military theory. His works include Imperial Policing (1934) and The Frontiers of Abyssinia: a retrospect (1937).
He attended both St. Columba's College, Dublin and the Royal Military Academy, Woolwich. As a soldier in the British Army, he fought against West African insurrectionists.
His 1934 book, Imperial Policing, is considered a must-read for political and military leaders involved in minor wars and low-intensity conflicts.
He was born in County Down, Ireland. His grandfather was Irish nationalist William Smith O'Brien.
He and Niccolo Machiavelli both wrote classic books on war and politics.