Abstract
This paper argues that the remarkably widespread enthusiasm in Britain after 1918 for an international air force was due to a confluence of two factors: the long-standing liberal belief that international law could prevent war, and the emergence of a new theory of warfare which claimed that the bomber was a weapon which could not be defended against. The origins of the international air force concept in the 1920s, its apogee in the 1930s, and its decline (and revival) in the Second World War are examined, showing that its fortunes rose and fell with internationalism and the knock-out blow.