Simulations and wargames offer powerful representations to model the mechanics and psychology of military operations that are inherently complex. They offer mechanisms to predict and assess the effectiveness of the mission plans and operations in achieving the military objectives. In this paper, we present a new approach to design the games rules of wargames using fuzzy rule bases, for quantitatively evaluating the effectiveness of air tasking missions. We determine the comparative damage relative to intended damage for a target, taking into account the effects of operational characteristics to compute possibilistic damage to the target as opposed to the probability of damage to the target. The cookie-cutter method to compute the damage is modeled as a fuzzy variable. Effectiveness of the mission is obtained by comparing the damage to targets with the cost and significance of the target in meeting the mission objectives. Damage assessment computation to targets using fuzzy rule bases gave more realistic results when used in field training and deployment of the system.