The Marine Corps MOS 5939 is for Aviation Communication Systems Technicians. These technicians maintain and supervise the maintenance of radios and communications systems for the Marine Air Control Group. They work with electronic equipment in the Marine Air Command and Control Systems network. This equipment supports air defense, weaponry, surveillance, radio communication, data monitoring, and air traffic control.
Other MOSs in the 59 field include:
5948 Aviation RADAR Technician
5951 Aviation Meteorological Equipment Technician
5952 Air Traffic Control Navigational Aids Technician
5953 Air Traffic Control RADAR Technician