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A CH-46 Sea Knight helicopter launches countermeasures (flares)

Fortification, a passive countermeasure

A countermeasure is a measure or action taken to counter or offset another one. As a general concept it implies precision, and is any technological or tactical solution or system (often for a military application) designed to prevent an undesirable outcome in the process. The first known use of the term is in 1923.[1]

Countermeasures can refer to the following disciplinary spectrum:

  • defense
  • medicine
  • materials engineering
  • electro-magnetic engineering
  • policing
  • Information technology
  • Law
  • Diplomatic security
  • Pollution prevention

Defense countermeasures are often subdivided into "active" and "passive" countermeasures.


"Active" countermeasures 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 soft-kill 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 majorly impeded are designated hard-kill measures. Both are further described in active protection systems.


"Passive" countermeasures include:

See also


  1. Meriam-Webster Dictionary "Countermeasure" defined

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