The AN/APR-39 threat warning system is a radar warning receiver, operating in the C through K frequency bands, which also can be a electronics countermeasures suite controller. In various versions, it is deployed on transports, special operations, electronic warfare aircraft, including helicopter, fixed-wing, and tilt-rotor types. Developed for the U.S. Army, it is used by a number of countries; the latest version is the AN/APR-39A(V)2.
The system was manufactured by Northrop Grumman and now by Litton, using a spiral evolution model in which the original APR-39 has become a fully digital system in the (V)2 model. More and more requirements are being found, such as defending civil aviation from terrorist threats. 
Early models lacked an integrating role, requiring direct aircrew interpretation since this system has no Emitter Identification Data (EID) software, now referred to as Mission Data Sets (MDS). In its system control role, the modern unit is considered the heart of the manufacturer's Suite of Integrated Sensors & Countermeasures (SISCM)  The device alerts the crew both with visual indications on a multifunction display as well as audio warnings of critical threats.
It provides coverage for C/D and E through J band continuous wave (CW) radar. The system has the capability of detecting most pulse radars normally associated with hostile surface-to-air missiles, airborne intercepts, or anti-aircraft artillery.
It can interface with the AN/AVR-2 and AN/AAR-47 laser warning receivers, AN/ALQ-136 pulse radar jammer ,and AN/ALQ-162 continuous wave radar jammer. It can use the AN/ALE-47 expendable dispenser and towed decoy controller, although the ALE-47 is the suite controller on a number of higher-performance aircraft. Cost-effectiveness and technical considerations generally lead at least some electronic warfare components to be optimized for different aircraft performance ranges, although commonality is always desirable.
- AH-1 : The first dedicated attack helicopter, introduced in the Vietnam War by the U.S. Army, but continuing to be produced in a redesigned version that meets the light attack needs of the United States Marine Corps
- AH-64 Apache : A United States Army attack helicopter capable of day/night missions in all weather.
- CH-47 Chinook : Medium transport helicopter developed by the U.S. Army and used by a wide range of countries ; MH-47 special operations variant
- UH-60A/L, UH-60Q (MEDEVAC) : A family of light transport helicopters used by the U.S. services, including the standard troop carrier UH-60 Blackhawk, naval rescue and surface/subsurface warfare, and the MH-60 special operations variant that is not really a Black Helicopter but instead very, very dark gray ; utility, MH-60K special operations, UH-60Q medical operations
- OH-58 Kiowa Warrior : A United States Army helicopter with extensive sensors for surveillance and guiding weapons fired by other air or ground weapons platforms, and also is a light attack helicopter on its own rights.
- V-22 Osprey : Military tilt-rotor aircraft capable of vertical takeoff as a rotary-wing helicopter, but faster horizontal flight using after converting its rotary-wing helicopter blades to propeller blades on a fixed-wing.
- KC-130 : A United States Marine Corps airborne tanker, which flies from land bases, and is frequently used to refuel Navy as well as Marine aircraft
- "AN/APR-39 Radar Warning Receiver (RWR)", Globalsecurity
- Hooton, E.R. (December 2005), "Fighting an invisible threat: air warfare involves both visible and invisible battlefields and the latter becomes more demanding every year—having extended from combat aircraft to support aircraft and now down to the helicopters and even civil aviation", Armada International
- Northrop Grumman, APR-39B(V)2 Suite of Integrated Sensors & Countermeasures (SISCM)