The purpose of this paper is to further deepen the knowledge about defence against amphibious assaults. Few theorists have embarked on the task to describe what it takes to defend against an amphibious assault. Due to the few cases with a successful outcome in favor of the defender, a severe lack of empirical proof for the theories exists. The paper has through a method of theory development created three different hypotheses from a study of the existing theoretical framework. These hypotheses then went through a theory test to try and falsify their impact corresponding to two cases with a successful outcome from the defenders perspective. The results of this study shows that the factors Deny sea – and air control and Clear command contribute to the successful defence against an amphibious assault. The factor Target priority was through the test falsified in its original description and changed in order to advance the theory further.