The advent of missile seekers with dual-mode millimeter wave and infrared common-aperture sensors has led to a requirement to develop the simulation tools necessary to test these systems. Traditionally, one of the most important techniques for supporting systems development has been a full seeker hardware-in-the-loop simulation. The development of simulation facilities capable of supporting the new generation of advanced dual-mode guided systems has been limited due to some major technological challenges which are yet to be solved. This paper provides an overview of the development of such a simulation facility at the U.S. Army Missile Command for supporting hardware-in-the-loop simulations of dual- mode systems. The major technological challenges which limit common-aperture dual-mode simulator development are presented with the current approaches which are being taken to overcome these challenges. A description of the dual-mode simulator capable of providing simultaneous imagery to both sensors of a common-aperture seeker is provided.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.