Remaining ahead of the enemy in all circumstances is crucial to any military power. Geographic information systems (GIS) can provide the military commander with geospatial information about the theatre of war to assist with the planning and execution of a mission. Unfortunately, technology usually comes at a price. GIS is no exception. The cost of acquiring and maintaining GIS software licenses, as well as training staff in the use of the software, needs to be considered. The question arises whether open source software, which can be used without any software license expenses, is a feasible alternative in military operations. The problem is that the perception exists that open source GIS software is neither user-friendly nor mature enough to be used in military operations. This study evaluates the functionality of an open source desktop GIS product in a military operations use case. A list of specific GIS functionalities was compiled based on the literature study and by developing a use case. The functionalities were executed in QGIS. Results were compared against results of the same functionalities in ArcGIS, which is widely used in military operations. Results show that all GIS functions tested by this study could be performed by both software products. These results are interesting because it means that FOSSGIS can be successfully deployed by units or directorates that has limited funds available to expand the existing GIS capabilities for military operations.