This paper describes the research and development work performed in the last ten years at the University of Zagreb and some other institutions in Croatia on design and development of state-of-the-art combat and security-related educational and training simulators. This overview paper begins with a conceptual description of individual and crew training simulators for antitank guided missiles, low altitude air defense missiles and MIG-21BIS fighter aircraft. Design and development concept of hardware-in-the-loop simulators for real time testing of newly developed digital signal processing guidance and control system is also presented. Then the authors describe the design and development of high-resolution tactical simulations and operational aggregated combat simulations. Finally, the paper presents a theoretical approach to modeling and simulation of national power and national security.