Assistant Lecturer in History (1947), Lecturer (1950–1953), dosent (engelsk: Reader) i War Studies og etterhvert professor, War Studies (1953–1963), King's College London. Chichele Professor of History of War (fra 1977) og Fellow, All Souls College (fra 1968 to 1980). Regius Professor of Modern History og Fellow of Oriel College, Oxford [Honorary Fellow, 1990] (from 1980 to 1989). Robert A. Lovett Professor of Military and Naval History, Yale University (fra 1989 to 1993). Quondam Fellow, All Souls College (fra 1980 to 2014). Honorary Fellow, All Souls College (fra 2014).