The general requirements, plan, and equipment for on-board voice communication in military aircraft are described. The characteristics and functions of essential components, including speech projectors, receptors, and intervening electronic equipment, are illustrated by conventional current and improved equipment. This equipment and its design problems are demonstrated in relation to requirements dictated by personnel protection, respiration, and altitude provisions. The electrical, mechanical, and acoustical characteristics of prospective transducers, conventional and unusual, including microphones, earphones, loudspeakers, and accelerometers, are reviewed as part of a morphological study of speech projection and reception techniques. Evaluation is based upon standard electrical and acoustical ratings and newly devised ratings appropriate to the problem, as well as engineering judgment regarding adaptability to flight systems, including wearability. The comparisons show great promise for the electrostatic transducer as an earphone or loudspeaker.