As France fell before the German onslaught in the summer of 1940, the British would adopt a similar position in their diplomacy towards the criticality of American aid to their continuing resistance. In his correspondence with Roosevelt, Churchill would repeatedly raise the prospect of British defeat without American aid. At one stage, this approach was characterised by a Foreign Office official as ‘… rather like blackmail, and not very good blackmail at that’. These assertions of critical dependency informed aircraft supply which remained at the forefront of the Anglo-American supply relationship through Roosevelt's ‘all aid short of war’ support for Britain throughout the crisis of 1940 and the evolution of Lend-Lease which followed. It can be assumed that this approach was a product of the exceptional circumstances of 1940 but, as Herodotus indicates, it had a long pedigree in diplomacy. The key point is to determine how far British supply diplomacy in 1940 reflected genuinely critical military needs, and how far it served broader diplomatic goals.