Defending against an amphibious operation is one of the most complex operations in warfare, especially for a small coastal state. Despite this, there is only a limited amount written about how a small coastal state should defend itself against an amphibious operation. This study explains how a smaller coastal state manages to delay an amphibious landing despite being disadvantaged. The purpose of this paper is to explain how the Norwegian coastal defense managed to delay the German invasion of Oslo on April 9, 1940. The research was conducted using the qualitative text analysis method, to obtain a good overall picture of the invasion with several independent sources. Jacob Børresen's theoretical framework, which deals with how smaller coastal states should defend themselves against overwhelming resistance, was used to analyze the empirical material. His theory is broken down into four analytical dimensions: Coast artillery, Robust command structure, Combined defense and Intelligence. The results show that the main success factor for the Norwegian coastal defense was their coastal artillery, that sank the German cruiser Blücher. The conclusions drawn from the study are that good leadership and timely intelligence are vital for the coastal artillery to be effective.