This paper investigates a display manipulation designed to support movement tasks where the location of a threat is uncertain and dynamic. The problem is analogous to that of a naval transportation task, where a ship has to move from one port to another under threat from several enemies of which only the initial positions are known. The display manipulation visualizes a time-dependent constraint on the area where an enemy can be, given its initial position and maximum speed, and adjusts the shape to the environment. The region outside this area represents a field of safe travel where the transport ship can move safely. Forty participants without prior knowledge of the task completed sixteen trials in an experiment that contrasted with and without visualization, and controlled for learning effects. The results suggest that the visualization significantly improved performance in the movement task and that it had a large effect. The visualization also significantly reduced variance in performance, which suggests that it generated a more consistent behavior among participants. It was also easy for the participants to make effective use of the visualization, and once exposed to the visualization, the learning transferred to a condition without the visualization. This study have practical utility for designers of combat information systems as the results indirectly suggest that people have difficulties in inferring the locations of targets of which they only have fragmentary information. Including similar visualizations in the design may consequently increase overall system performance.