Identification friend or foe

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Identification, friend or foe (IFF) is a combat identification system designed for command and control. It uses a transponder that listens for an interrogation signal and then sends a response that identifies the broadcaster. IFF systems usually use radar frequencies, but other electromagnetic frequencies, radio or infrared, may be used. It enables military interrogation systems to identify aircraft, vehicles, or forces as friendly, as opposed to neutral or hostile, and to determine their bearing and range from the interrogator. With the successful deployment of radar systems for air defence during early World War II, combatants were immediately confronted with the difficulty of distinguishing friendly aircraft from hostile ones; by that time, aircraft were flown at high speed and altitude, making visual identification impossible, and the targets showed up as featureless blips on the radar screen. This led to incidents such as the Battle of Barking Creek, over Britain, and the air attack...

Read on Wikipedia · Image SRA Michele G. Misiano, USAF., Public domain