Simulation Applications and C4ISR Systems There is a strong necessity to solve the interoperability issue between information systems used for Command, Control, Computing, Communications, Intelligence, Surveillance, and Intelligence (C4ISR) and combat simulation systems. Interoperability is an operationally driven requirement in several application domains of combat simulation systems and it is stated in milestone documents such as the US DoD Modeling and Simulation Master Plan 1 and the NATO Modeling and Simulation Master Plan. 2 Within the simulation application domain of training and exercises appropriate simulation systems are used to create a synthetic environment for the trainees that is supplied to the C4ISR systems used by the soldiers in the field to "train them as they fight." Hence, the simulation systems used for computer-assisted exercises (CAX) have to be able to provide the necessary input to the C4ISR systems used by the trainees. Additionally, the orders given by the trainees to the simulated units have to be brought into the simulation systems as efficiently as possible, which implies that, as a minimum, the orders have to be transferable from the C4ISR application to the embedded simulated environment. Modeling and simulation (M&S) have also been applied successfully in simulation-based acquisition (SBA) for several years. Simulation systems are used to build a synthetic environment that dynamically generates test data for the C4ISR systems in the acquisition process. Furthermore, M&S is used to simulate new components to be introduced into the C4ISR systems. This application also leads to the requirement for interoperability between the