This study addresses energy security from the perspective of comprehensive nationaldefence, especially the interaction between military and civilian aspects of defence. Civilian infrastructure is seldom configured or developed with defence in focus. Therefore, with the aim offacilitating a system-level discussion, this study takes two steps. The first step is to develop indicatorsfor assessing energy security in a comprehensive national defence setting. The second step is toqualitatively assess the effect on energy security from three different energy development scenariosrelated to either the development of local solar, wind, and bio-power production and storage; anincreased resilience of the high voltage electric power transmission system; or an increase in largehydropower and nuclear power production. The study identifies that there are positive systemiceffects of increasing the diversity of the energy system, especially for solutions that do not needexternal supply and do not risk creating large-scale effects if attacked. However, these changes to theenergy system also lead to local changes that affect warfighting and defence. Such changes can bemet by updated tactics and technology that would also give the defending force an advantage.