This is the first comprehensive account of how intelligence influenced and sustained British naval power from the mid nineteenth century, when the Admiralty first created a dedicated intelligence department, through to the end of the Cold War. It brings a critical new dimension to our understanding of British naval history in this period while setting naval intelligence in a wider context and emphasising the many parts of the British state that contributed to naval requirements. It is also a fascinating study of how naval needs and personalities shaped the British intelligence community that exists today and the concepts and values that underpin it. This compelling new history will have wide appeal to all readers interested in intelligence and its crucial impact on naval policy and operations.