The ionosphere is a critical element in the design and operation of many military RF systems. While judicious engineering choices, such as transmission frequency, can mitigate many ionospheric effects, the research scientist and engineer are being asked to meet ever more demanding operational requirements. These, in turn, require ever more sophisticated situational awareness, mitigation, and exploitation techniques, which are being variously realized against a backdrop of evolving ground- and space-based instrumentation. The latter, in combination with improved modeling and assimilative techniques, promises a new generation of more capable real-time ionospheric models. Through examples this paper describes the benefits and problems associated with the ionospheric medium. HF communications and space radar systems are discussed as exemplars, and an emphasis is placed on the need to understand the engineering details of those systems if ionospheric research and development is to provide its full benefit.