Defense Modeling & Simulation (M&S) techniques are used for developing the efficiency and economics of national defense at operational level so that it maintains interoperability and reusability in sustainability for the following process of the war simulation. However, the lack of conceptual models was one cause of limiting the interoperability and reusability in defense M&S areas. In this paper, the Conceptual Model of the Mission Space (CMMS) is studied as preliminary process for the defense M&S. The conceptual modeling framework called CMMS-K (Conceptual Model of the Mission Space-Korea) is suggested using a case example in consideration of the Korean Army specification and characteristics. The practicality of CMMS-K is evaluated through the ontology development for military scenarios. It is expected that the gap between the theoretical approach and the practical perspective of defense M&S can be diminished through the use of these approaches.