Active protection system An active protection system is a system ( usually for a military application ) designed to prevent anti - armor line - of - sight weapons from acquiring and / or destroying a target . Electronic countermeasures that alter the electromagnetic , acoustic or other signature ( s ) of a target thereby altering the tracking and sensing behavior of an incoming threat ( e . g . , guided missile ) are designated softkill measures . Measures that physically counterattack an incoming threat thereby destroying / altering its payload / warhead in such a way that the intended effect on the target is severely impeded are designated hardkill measures . Softkill measures . Softkill measures are applied when it is expected that a sensor - based weapon system can be successfully interfered with . The threat sensor can be either an artificial one , e . g . , a solid - state infrared detector , or the human sensory system ( eye and / or ear ) . Softkill measures generally interfere with the signature of the target to be protected . In the following the term " signature " refers to the electromagnetic signature of an object in either the ultraviolet ( wavelength : 0 . 3 - 0 . 4 µm ) , visual ( 0 . 4 - 0 . 8 µm ) , or infrared ( 0 . 8 - 14 µm ) spectral range as well as cm - radar range ( frequency : 2 – 18 GHz ) , mmw - radar ( 35 , 94 , 144 GHz ) and finally sonar range ( either 50 Hz - 3 kHz and / or 3 – 15 kHz ) . One or more of the following actions may be taken to provide softkill : Softkill countermeasures can be divided into on - board and expendable countermeasures . Whereas on - board measures are fixed on the platform to be protected , expendable measures are ejected from the platform . " Preemptive action " of countermeasures is directed to generally prevent lock - on of a threat sensor to a certain target . It is based on altering the signature of the target by either concealing the platform signature or enhancing the signature of the background , thus minimizing the contrast between the two . " Reactive action " of countermeasures is directed toward break - lock of a threat already homing in on a certain target . It is based on the tactics of signature imitation , augmentation , or reduction . Aerial countermeasures . Generally one has to distinguish between infrared and radar countermeasures . The wavelength range between 0 . 8 and 5 µm is considered as Infrared ( IR ) , the frequency range between 2 and 18 GHz is considered as Radar . In the wake of shoulder - launched missile attacks against civilian passenger and cargo airliners in the early 2000s , various agencies investigated the feasibility of equipping countermeasures such as chaff and flare s . Many commercial carriers found the estimated price of countermeasures to be too costly . However , the Israeli airline El - Al , having been the target of the failed 2002 airliner attack , in which shoulder - launched surface - to - air missiles were fired at an airliner while taking off , began equipping its fleet with radar - based , automated flare release countermeasures from June 2004 . This caused concerns in some European countries , regarding the possible fire hazard at civilian airports , resulting in banning such aircraft from landing at their airports . In 2007 , Saab announced a new infrared countermeasure system called CAMPS that does not use pyrotechnic flares , thereby directly addressing these concerns . IR - decoy flares . IR - decoy flares serve to counter infrared - guided surface - to - air missile s ( SAM ) or air - to - air missile s ( AAM ) and can be expelled from a craft according to an anticipated threat in defined sequences . Radar decoys . To counter radar - guided missiles , chaff is used . These are copper nickel - coated glass fibers or silver - coated nylon fibers having lengths equal to half of the anticipated radar wavelength . Naval decoys . Land and sea - based forces can also use such countermeasures , as well as smoke - screen s that can disrupt laser ranging , infrared detection , laser weapons , and visual observation . Hardkill measures . Except for countering intercontinental ballistic missile s , hardkill measures generally refer to measures taken in the so - called " end - game " shortly before a warhead / missile hits its target . The hardkill measure in general physically affects the incoming warhead / missile by means of either blast and / or fragment action . The action may lead to : Reactive armor . An example of a hardkill countermeasure is the reactive armor found on many modern armored vehicles . Antiaircraft weapons . Another example of hardkill countermeasures is the use of short - range missiles or rapid - fire guns to protect warships and fixed installations from cruise missile , bomb and artillery attacks . Anti - ballistic missiles . Countermeasure s are a complicating factor in the development of anti - ballistic missile defense systems targeting ICBM s . Like aircraft , ICBMs theoretically could evade such systems by deploying decoy s and chaff in the midcourse phase of flight . Novel proposed chaff mechanisms describe the creation of a " threat cloud " by deploying large aluminized PET film balloons which could conceal a warhead among a large number of inert objects having similar radar profiles . Potential performance problems . Clutter . Mountains and neighbouring vehicles reflect radio waves , thus creating radar clutter , which adversely affects radar - detection and radar - lock performance . Top attack munitions . Top attack ATGMs like FGM - 148 Javelin ( USA ) , Trigat ( Germany ) and Spike ( Israel ) attack the tank turret ' s top , requiring the active protection system to attack nearly vertically , for which turret might have not been designed . The same is true for an RPG being fired in a steep downward angle from an elevated location at the road below . References . DIRCM and AVePS