The U.S. Army Aviation and Missile Command (AMCOM) Advanced Simulation Center (ASC) provides hardware-in-the-loop (HWIL) simulation support to Program Executive Officers (PEO) and Project Managers (PM) who are responsible for developing and fielding precision guided missiles and sub-munitions for the U.S. Army. The ASC is also engaged in cooperative HWIL simulation tasks supporting other Armed Service Agencies, NATO and other U.S. allies. HWIL simulation provides a means of exercising missile guidance and control hardware in simulated flight, wherein the missile sensors are stimulated with input signals which make the system behave as though it were in actual operation. Real-time computers are used to control the target and countermeasure signatures and battlefield scenarios. Missile flight dynamics, responding to the commands issued by the guidance and control system hardware/software, are simulated in real-time to determine the missile trajectory and to calculate target intercept conditions. The ASC consists of 10 HWIL simulation facilities developed over a period of 20 years. These facilities contain special purpose infrared and RF signal generation equipment, flight motion simulators, radiation chambers, optics, and computers. They provide in- band target signatures, countermeasures, and background scenarios in the microwave, millimeter wave, infrared and visible regions of the electromagnetic spectrum. The ASC HWIL simulation facilities are an important source of test and evaluation data and have a critical role in all phases of a missile system life cycle. The development of a new generation of missile systems that use multi-spectral seekers has imposed unique and difficult requirements on ASC HWIL simulation facilities. For the past three years, the U.S. Army Aviation and Missile Command (AMCOM) has been developing a HWIL simulation facility to test common aperture multi-spectral missile seekers. This paper discusses the problems encountered during the development of this facility, the solutions, and the resulting capability of this unique HWIL simulation facility.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.