01	Telemetry	Data transmission techniques and equipment including transmitters, receivers, and antennas. Includes acoustic, optical, wired and radio telemetry. For biotelemetry, See 23/01, Biomedical Instrumentation and Bioengineering.
02	Radio Communications	Communication by radio waves; Microwave communications; Television communications. Includes radio transmitting and receiving equipment, radio broadcasting, radio relay stations, radio scanning. For radiotelemetry, See 25/01, Telemetry. For radiofrequency propagation, See 20/14, Radiofrequency Wave Propagation. For radio countermeasures, See 17/04/01, Radio Countermeasures.
03	Non-Radio Communications	Communications by means other than radio waves. For communication by radio waves, See 25/02, Radio Communications. For wired telemetry, See 25/01, Telemetry.
04	Voice Communications	Research and development in vocal communication; Speech intelligibility; Speech recognition; Speech analysis and synthesis. See also 12/09, Cybernetics.
05	Command, Control and Communications Systems	Includes command and control systems.