Encompassed within the scope of naval diplomacy, discussed in detail in Chapter 9, exists a grey area where force is used, or threatened, somewhere on an ambiguous margin between peace and war. Such operations are usually confronted by complex operational difficulties and moral dilemmas. They are therefore highly problematic to undertake. Nowhere was this more apparent, or more bitterly divisive, than in Britain’s last ‘war’ with France, fought in Europe, Africa and Asia between 1940 and 1942. Further, the geo-strategic peculiarities of that conflict placed the Royal Navy in an unenviable position as Britain’s reluctant military tool of choice. Its actions at Mers-el-Kébir in July 1940 would have profound consequences for both the balance of military power in the Mediterranean and future Anglo-French relations. This chapter explores the difficulties of operating in such ambiguous circumstances by setting the Anglo-Vichy conflict in its strategic context, examining the fateful operations of 3 July 1940 and analysing their impact upon subsequent events.