This paper considers capabilities and benefits of aircraft-sized radio/radar frequency anechoic chambers for Test and Evaluation (T&E) of Electronic Warfare (EW), radar and other electromagnetics aspects of air and ground platforms. There are few such chambers worldwide. Initially developed to reduce costs, timescales and risks associated with open-air range flight testing of EW systems, their utility has expanded to most areas of platforms’ electromagnetics’ T&E. A key feature is the ability to conduct T&E of nationally sensitive equipment and systems, fully installed on platforms, in absolute privacy. Chambers’ capabilities and uses are described, with emphasis on key infrastructure and instrumentation. Non-EW uses are identified and selected topics elaborated. Operation and maintenance are discussed, based on experiential knowledge from international use and the authors’ 30 years’ involvement with BAE Systems’ EW Test Facility. A view is provided of trends and challenges whose resolution could further increase chamber utility. National affordability challenges also suggest utility expansion to support continuing moves, from expensive and difficult to repeat flight test and operational evaluation trials, towards an affordability-driven optimal balance between modelling and simulation, and real-world testing of platforms.