A military direction-finding system is used to detect radio frequency emission in the battlefield by multiple directional detectors and locate the emitter. Since directional information from a detector has limited accuracy and includes some random angular error, the location of the emitter is estimated from the directional information of the three directional detectors by a well-known algorithm. The detection probability is affected by the relative angles and distances of the detectors, the distribution of the enemy troops that are potential emitters, and the geographical situation. We examine how the detectors should be located in order to maximize the detection probability. We propose a way of determining the optimal configuration of the detectors. In order to evaluate each configuration alternative, we propose the use of the size of the common area that is formed by the three detected directions. By a preliminary experiment, we identify that the size of such detection area is a good indicator for the detection probability. We formulate an optimization model for determining the optimal configuration by minimizing the weighted sum of the detection area sizes. By the simulated annealing method, we determine the optimal configurations for experimental cases. The optimal detector configurations that are determined by the proposed method show higher detection probabilities that the conventional configuration rule.