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.
Countermeasures can refer to the following disciplinary spectrum:
Defense countermeasures are often subdivided into "active" and "passive" countermeasures.
In military applications, "active" countermeasures which 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 severely impeded, such as close-in weapon systems, are designated hard-kill measures. Both types are further described in active protection systems.
"Passive" countermeasures include: