Sir Oliver Franks served as British Ambassador to the US between 1948 and 1952. This was a seminal period in postwar history, which saw the implementation of the Marshall Plan, the emergence of the Cold War, the signing of the North Atlantic Treaty, the Korean War and the assimilation of the former enemy powers of Germany (or the western part at least) and Japan into the international system. During these years, Britain was regarded as the principal ally of the US in the east-west confrontation. This gave British policymakers an opportunity to influence both US policy and international developments. The British Embassy in Washington therefore had the potential to play an important role; so too did the Ambassador. This was not automatic, however, and it needed a talented ambassador to make the most of the political circumstances. Sir Oliver Franks was an extremely able individual, who was capable of making such an impact. Trusted by the senior figures on both sides of the Atlantic, he quickly established himself as an indispensable mediator between the two nations. This analysis reveals a great deal about the condition of relations between Britain and America, the mechanics of co-operation and the impact of a singular individual on international relations.