Weapon target assignment is a weapon assignment problem with the objective of minimizing the expected survival value of targets. This problem must be quickly solved on the battlefield (i.e., in real-time). Considering the combined complexity and the strict time constraints, a fuzzy decision maker is proposed as an alternative to aid commanders in deciding on proper weapon assignments. The concept builds a fuzzy decision maker for a given data set by using extended grid partitioning based on a sensitivity analysis of input variables. The proposed decision maker is implemented and tested with several randomly sampled assignment instances on realistic scenarios. In addition, a larger-scale scenario is also considered to demonstrate the scalability of the approach. The results show that the proposed system exhibits satisfactory performance and is serviceable on the battlefield.