Thermal seeker

Infrared homing is a passive weapon guidance system which uses the infrared (IR) light emission from a target to track and follow it. Missiles which use infrared seeking are often referred to as "heat-seekers", since infrared is radiated strongly by hot bodies. Many objects such as people, vehicle engines and aircraft generate and emit heat, and as such, are especially visible in the infrared wavelengths of light compared to objects in the background.

Infrared seekers are passive devices, which, unlike radar, provide no indication that they are tracking a target. This makes them suitable for sneak attacks during visual encounters, or over longer ranges when used with a forward looking infrared system or similar cuing system. This makes heat-seekers extremely deadly; 90% of all United States air combat losses over the past 25 years have been due to infrared-homing missiles. They are, however, subject to a number of simple countermeasures, most notably dropping flares behind the target to provide false heat sources. This only works if the pilot is aware of the missile, and modern seekers have rendered these increasingly ineffective even in that case.

The first IR devices were experimented with in the pre-World War II era. During the war, German engineers were working on heat seeking missiles and proximity fuses, but did not have time to complete development before the war ended. Truly practical designs did not become possible until the introduction of conical scanning and miniaturized vacuum tubes during the war. Anti-aircraft IR systems began in earnest in the late 1940s, but both the electronics and entire field of rocketry was so new that it required considerable development before the first examples entered service in the mid-1950s. These early examples had significant limitations and achieved very low success rates in combat during the 1960s. A new generation developed in the 1970s and 80s made great strides and significantly improved their lethality. The latest examples from the 1990s and on have the ability to attack targets out of their field of view (FOV), behind them, and even pick out vehicles on the ground.

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