craft from friendly ones. Role in air warfare A very common area of ELINT is intercepting radars and learning their locations and operating procedures. Attacking forces may be able to avoid the coverage of certain radars, or, knowing their characteristics, electronic warfare units may jam radars or send them deceptive signals. Confusing a radar electronically is called a "soft kill", but military units will also send specialized missiles at radars, or bomb them, to get a "hard kill". Some modern air-to-air missiles also have radar homing guidance systems, particularly for use against large airborne radars. Knowing where each surface-to-air missile and anti-aircraft artillery system is and its type means that air raids can be plotted to avoid the most heavily defended areas and to fly on a flight profile which will give the aircraft the best chance of evading ground fire and fighter patrols. It also allows for the jamming or spoofing of the enemy's defense network (see electronic warfare). Good electronic intelligence can be very important to stealth operations; stealth aircraft are not totally undetectable and need to know which areas to avoid. Similarly, conventional aircraft need to know where fixed or semi-mobile air defense systems are so that they can shut them down or fly around them. ELINT and ESM Electronic support measures (ESM) or electronic surveillance measures are ELINT techniques using various electronic surveillance systems, but the term is used in the specific context of tactical warfare. ESM give the information needed for electronic attack (EA) such as jamming, or directional bearings (compass angle) to a target in signals intercept such as in the huff-duff radio direction finding (RDF) systems so critically important during the World War II Battle of the Atlantic. After WWII, the RDF, originally applied only in communications, was broadened into systems to also take in ELINT from radar bandwidths and lower frequency communications systems, giving birth to a family of NATO ESM systems, such as the shipboard US AN/WLR-1—AN/WLR-6 systems and comparable airborne units. EA is also called electronic counter-measures (ECM). ESM provides information needed for electronic counter-counter measures (ECCM), such as understanding a spoofing or jamming mode so one can change one's radar characteristics to avoid them. ELINT for meaconing Meaconing is the combined intelligence and electronic warfare of learning the characteristics of enemy navigation aids, such as radio beacons, and retransmitting them with incorrect information. Foreign instrumentation signals intelligence FISINT (Foreign