We present a tool box for functional testing of complex distributed IT systems specially tailored for the tactical environment. In order to construct suitable test beds for such systems we capture their 'ambient' infrastructure by means of virtualization and real-time simulation. As an example, we describe how our approach can be used for testing a complex distributed system consisting of (multiple instances of) a tactical command and control information system, a communications server system and a radio communications system. The combined system is part of the standard equipment of various German Army mobile platforms. Aside testing, our tool box also has many potential applications in the domain of training support.