An air force depends on air bases to conduct air operations. Although threats against air bases are extensive, nuanced, and complex, the academic literature on air base ground defence is deficient. Prior research shows that systematic mapping over base defence history is missing and historical factors for success is unknown. In comparison, the literature about air power’s ability to coerce and air power targeting is extensive. A prerequisite to project air power is that the air crafts are not lost on the ground.  The aim of this research is to increase the understanding of air power by develop an initial theory about air base ground defence. By using a hypothesis-deductive methodology, important factors are identified based on prior research. The factors are transformed into hypotheses, operationalized, and tested on two different cases. The analysis verifies, falsifies, or in some cases are not able to state the explanatory value off the hypothesis. The results indicate that depth and early warning are prominent factors for a successful air base ground defence. The theory needs more testing before the explanatory value can be confirmed or falsified for every factor. The role the intelligence service plays in air base ground defence and the study´s delimitations is identified as need for further research to expand and make the initial theory comprehensive.