The Scandinavian realms underwent considerable changes to their political institutions, social structures and economic exploitation models during the twelfth and thirteenth centuries, and the military institutions are no exception. The relatively decentralized military model of the Viking Age, which relied on peasant levies for large expeditions, was gradually replaced by smaller aristocratic fleets that in turn used the increasingly larger income of the aristocratic strata in order to build much larger warships. These considerable changes in military organization and shipbuilding, therefore, changed naval warfare in Scandinavia to a substantial degree.

The transformation of naval warfare during the twelfth century has never been considered from a holistic point of view. For example, in order to understand the changes in tactics, both the changes in the military institutions and the emergence of new types of warships should be taken into account. These three aspects of warfare – military organization, shipbuilding innovations and tactical approaches – can be discerned from a number of written and material sources. While the legal codes of the twelfth and thirteenth centuries have often been used when researching the changes in the military institutions, primary material that describes both shipbuilding and tactics has rarely been taken into account.