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Identification friend or foe
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<p>Identification, friend or foe (IFF) is a <a href="/facts/Combat_identification/ANQjz9NM">combat identification</a> system designed for <a href="/facts/Command_and_control/t1huKNbX">command and control</a>. It uses a <a href="/facts/Transponder/cmqcWPwE">transponder</a> that listens for an <i>interrogation</i> signal and then sends a <i>response</i> that identifies the broadcaster. IFF systems usually use <a href="/facts/Radar/jk9BTbFA">radar</a> frequencies, but other electromagnetic frequencies, radio or infrared, may be used. It enables military and civilian <a href="/facts/Air_traffic_control/G2cQebVb">air traffic control</a> 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. IFF is used by both military and civilian aircraft. IFF was first developed during <a href="/facts/World_War_II/2efV5L1U">World War II</a>, with the arrival of radar, and several <a href="/facts/Friendly_fire/huKuPn8V">friendly fire</a> incidents. </p><p>IFF can only positively identify friendly aircraft or other forces. If an IFF interrogation receives no reply or an invalid reply, the object is not positively identified as foe; friendly forces may not properly reply to IFF for various reasons such as equipment malfunction, and parties in the area not involved in the combat, such as civilian light <a href="/facts/General_aviation/gA0ozoWt">general aviation</a> aircraft may not carry a transponder. </p><p>IFF is a tool within the broader military action of combat identification (CID), the characterization of objects detected in the field of combat sufficiently accurately to support operational decisions. The broadest characterization is that of friend, enemy, neutral, or unknown. CID not only can reduce friendly fire incidents, but also contributes to overall tactical decision-making. </p><p>With the successful deployment of radar systems for <a href="/facts/Anti-aircraft_warfare/fHtGQpLy">air defence</a> during <a href="/facts/World_War_II/2efV5L1U">World War II</a>, 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 <a href="/facts/Battle_of_Barking_Creek/XLqY6zju">Battle of Barking Creek</a>, over Britain, and the <a href="/facts/Air_attack_on_the_fortress_of_Koepenick/vvtkyYYL">air attack on the fortress of Koepenick</a> over Germany. </p>