This dissertation analyzes the submarine problem in Sweden as an object of security politicization. It investigates how politicians and military officers dealt with the submarine incidents of the 1980s and 1990s, and how their actions were portrayed in the media. A popular assumption in modern literature on media and politics is that the media arena helps define the political arena—which players are important, what issues are placed on the political agenda, and which options are available for competitive political elites in democratic systems of government. By quantitatively analyzing the media image of the submarine “threat”, and comparing those results with indicators of public opinion and policy change, the dissertation investigates the influence of the media image on security policy over time. The results of the quantitative analysis inform a number of qualitative case studies, highlighting the important events and developments of the submarine threat and the causal mechanisms by which media and public opinion may have influenced Swedish security policy. The dynamics by which the political and military levels interact in creating a public image of the submarine threat are a particular focus in the strategically selected cases over the period—including both events that can be seen as escalating threat perceptions and those that have de-escalated such public anxieties. In the end, it is found that several problems relating to organizational coherence, institutional legitimacy and political controversy led the uncontrolled fashion in which the submarine issue became a publicly perceived threat.