In the last episode we looked at the development of the world's navies during the interwar period. To compliment that I thought we'd do something similar with aerial warfare. It is easy to forget in 1939 aviation was still very much in its infancy, and especially aerial warfare.

Theorist such as Giulio Douhethad highlighted the importance of controlling airspace, Douhet also advocated that idea that a nation could bomb its way to victory. Other countries such as Germany envisaged the plane in tactical roles, supporting the army. So at the outbreak of WWII each air force was prepared to a fight a war, just not necessarily the war their enemy was expecting to fight.

Joining me today is Frank Ledwidge.

Frank is a senior fellow in Air Power and International Security, at the Royal Air Force College - Cranwell. Not only does he teach this stuff, he's written a book on the subject 'Aerial Warfare: The Battle for the Skies'.