This paper compares the efficiency of using a standard direct-manipulation graphical user interface (GUI) with that of using the QuickSet pen/voice multimodal interface for supporting a military task. In this task, a user places military units and control measures (e.g., various types of lines, obstacles, objectives) on a map. Four military personnel designed and entered their own simulation scenarios via both interfaces. Analyses revealed that the multimodal interface led to an average 3.5-fold speed improvement in the average entity creation time, including all error handling. The mean time to repair errors also was 4.3 times faster when interacting multimodally. Finally, all subjects reported a strong preference for multimodal interaction. These results indicate a substantial efficiency advantage for multimodal over GUI-based interaction during map-based tasks.