The aim of this report is to find a methodology to formalize the combat effectiveness for ground combat and ground-based air-defence (GBAD). Combat effectiveness can be defined as a measure of how well a combat task has been performed. There are direct and indirect effect. The direct effect is caused by an action, i.e. by interception of the threats. The indirect effect is on the other hand not preceded by an action. The existence of the unit and its potential to act is sufficient to affect the adversary's capability to achieve his goals. For the case of ground combat, the combat effectiveness of a weapon system has been formalized in terms of four parameter dimensions containing attributes of the system, opponent, surroundings and the combat task. An analysis of the combat tasks given to a platoon has narrowed down the relevant tasks for weapon systems assessment. A conceptual methodology is proposed for assessment of combat effectiveness of a weapon system used in ground combat at a platoon level. For the case of GBAD, formalization of combat effectiveness has been based on a GBAD unit's combat tasks. The analysis has been performed as a sensitivity study with OPaL, a simulation tool for analysing GBAD scenarios on a tactical level. A reference scenario which describes the combat task Protect has been set up in OPaL. The GBAD unit consists of fire units and sensors, and the combat task is to protect the asset from being hit by cruise missiles. In the sensitivity study, a variation of antenna height has been made, in order to analyse how this parameter affects the hit count on the protected asset, and accordingly how it affects the combat effectiveness. To assess the underlying causes to the results, different parameters such as detection time, reaction time, interception time and distance to the protected asset have been analysed. In order to identify patterns and correlations between parameters, the results have been visualized with different tools outside OPaL. In order to conduct a more complete analysis of combat effectiveness, new functionalities would need to be added in OPaL. Further work could include exploring methods for experiment design and methods for assessment of uncertainties in OPaL. Beyond simulations, there are other aspects of combat effectiveness that need to be considered and analysed in future work: the value and serviceability of the protected asset, performance and cost of the GBAD system, human factors and uncertainties regarding the adversary's actions. The combat effectiveness has been analysed in OPaL on a tactical level. However, it can be analysed on an operational level including coordination of other combat arenas. Therefore, formalization of combat effectiveness needs to be carried out from several aspects and at different levels.