The coast is a domain characterized by great complexity based on its dynamic and challenging nature, which can create both opportunities and challenges for attackers and defenders. The purpose of this study is to investigate Geoffrey Till's theory of defence against amphibious operations and to increase an understanding of how military resources can be used to achieve success in defence in the event of a military attack from the sea. Research and theory development in this area have long been under-prioritized and Till has created a relatively unique theory, based on the prevailing research situation. These are arguments that strengthen the reason for examining the theory and field further. Through a theory-testing case study, the Battle of Wake Island and Operation Avalanche are analyzed to ascertain to what extent empirical evidence is given to the chosen theory. In this way, the explanatory capacity of the theory is determined and whether its credence is strengthened or weakened. The study discloses that Till's theory successfully explains the outcome of the first case however not the second. The analysis shows that a defence that acts on and adjacent to land contributes to success, which Till's theory does not emphasize. The study indicates that the theory is underspecified as it does not give any indication of how to prioritize between the different areas of the theory, which indicates that wone should be vigilant against the explanatory value of the theory.