This thesis examines, by reference to the political, institutional, organisational, personnel, operational, methodological and technical aspects of naval intelligence work, the developmental aspects of its history from 1880 to 1945. By analysing specific naval operations and discussing the strategic and tactical ramifications of intelligence it seeks to throw light on the impact of intelligence on naval warfare in this period. In so doing it reveals the place of intelligence in the general naval history of the period. It is not a definitive history, but rather a discursive analysis of those aspects considered the most important. In the pre-1914 era the N.I.D. was the heart of the emergent Naval Staff, involved in strategic planning at the highest level. World War I brought the need for an operational intelligence organisation, with the priority of locating, identifying, and deducing the intentions of major German units. Experience in war revealed the necessity for a clear definition of the relationship between the Operations Division and the N.I.D. The use of radio intelligence and cryptanalysis gave N.I.D. great operational successes and Admiral Hall the opportunity to involve N.I.D. in political issues.The latter led to the review of N.I.D.'s role post 1918 and, in part, its run-down. The inter-war period witnessed N.I.D.'s decline as the most dynamic and influential Naval Staff department. Until the foundation of O.I.C. and the coming of war N.I.D. was a backwater. World War It witnessed a re-vitalisation, a more structured and tightly controlled N.I.D., and the D.N.I.. as an important echelon of the C.O.S. and J.LC. organisations. N.I.D. regained its previous supremacy and was instrumental in the process towards intelligence integration at the end of World War U. It scored great operational successes. The function of intelligence is demonstrated as being paramount in the naval organisation and critical to the interests of the State. Its maintenance was contingent upon variables which, throughout this period, were neither constant nor always recognised.