 Air policing is a purely defensive mission.Since the 1970s, NATO has established a comprehensive system of air surveillance and airspace management means, as well as Quick Reaction Alert (QRA) assets for intercepts (QRA(I)) provided by its member nations.By means of radar sites, remote data transmission, Control and Reporting Centres (CRCs) and Combined Air Operations Centres (CAOCs) the Alliance ensures constant surveillance and control of its assigned airspace 24 hours a day and 365 days a year.