Most armed forces maintain varying levels of readiness by the troops to engage in combat due to economic considerations which vary from minutes to months. In modern armed forces troops designated special forces are usually those kept at the highest state of readiness for combat, and are often alerted only a few hours before being committed to combat. Where time is of the essence in military action being initiated, the troops, such as pilots of interceptor aircraft, may be kept in constant state of combat readiness.
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