On 10 February 1964 during naval night exercises off the south coast of Australia, the destroyer HMAS Voyager was lost after colliding with the aircraft carrier HMAS Melbourne. 82 men were killed. Following the collision, there were two Royal Commissions that sustained a political controversy that lasted for over four years. This thesis examines the loss of Voyager as a watershed in the operational and administrative history of the RAN and as a major event in Australian national history. This study has four broad objectives: to describe the loss of Voyager and the long running controversy that accompanied the disaster; to offer a convincing explanation of the causes of the collision and why two royal commissions concluded that the causes for the disaster were inexplicable; to assess the effect on the RAN, in terms of specific reforms and its influence on Service culture and professional ethos, of the disaster and the inquiries that followed; and finally, to analyse the loss of Voyager as a media and political cause celebre in Australian history. As so little has been written about Voyager using primary sources, this thesis was committed to detailed description of events as well as analysis of themes. This thesis draws upon an extensive body of primary source material in the form of official naval and Royal Commission records to which complete access was given; several large collections of private papers; over one hundred interviews with principal participants; and comprehensive files of press cuttings. The discussion seeks to demonstrate that a series of naval accidents preceding the loss of Voyager contributed in a substantial way to shaping the public reaction to, and political handling of, the disaster; that the method of inquiry played a major role in generating public and political disquiet; that the collision was both a catalyst and stimulus to change in naval operations and reform in naval administration; that the inability of two Royal Commissions to ascertain the causes of the collision and then to public suspicion of a cover-up; and, that the collision was most probably caused by the incorrect relaying of a tactical signal on the bridge of Voyager. The loss of HMAS Voyager appears to be a key event in the development of the RAN, not as a direct result of the collision or its causes, but as a consequence of its long and controversial aftermath.