Flak

NATO defines air defense as "all measures designed to nullify or reduce the effectiveness of hostile air action." They include ground and air based weapon systems, associated sensor systems, command and control arrangements and passive measures. It may be used to protect naval, ground and air forces wherever they are. However, for most countries the main effort has tended to be 'homeland defence'. NATO refers to airborne air defence as counter-air and naval air defence as anti-aircraft warfare. Missile defence is an extension of air defence as are initiatives to adapt air defence to the task of intercepting potentially any projectile in flight.