In agreeing to accept US nuclear weapons in 1959, and to conditions which paved the way for its participation in US missile defence programmes in 1981, Canada reversed two of its firmly held defence policy positions. Both of these reversals were intimately linked to the dynamics of the North American Air, later Aerospace, Defence Agreement (NORAD) signed by Canada and the United States in 1958 to institutionalize the joint air defence of the continent. Traditional analyses of Canadian defence policy decision-making suggest that the policy reversals were the inevitable capitulations of a middle power to its alliance commitments and the exigencies of the international security environment. Reflecting a social construction understanding of power relations, this article argues that the 'inevitability' of the capitulations resided instead in three specific dynamics; the nature of the political/military relationship in Canada, the phenomenon of Canadian military professionalism, and the transnational/transgovernmental nature of the Canadian/US cooperative military relationship. These three dynamics interacted to create a divergence of understandings between the Canadian political decision-makers and the military as to how best to pursue Canadian security interests, as well as the reasons and the means for the Canadian military to significantly shape Canadian defence policy. In essence, the three interacting dynamics were/are largely responsible for introducing an element of 'unanticipated militarism' to the Canadian political decision-making environment.