The rotation places four fighters on patrol, four on alert, and the rest in preparation or maintenance. If the airborne patrol intercepts a threat, the alert group launches and another group must be brought up immediately. This pattern explains the long-standing rule of thumb that a proper four-aircraft patrol needs about eighteen fighters. Navies were developing these cycles by the late 1920s and early 1930s, before radar became available. Lookouts, scouts, and anti-submarine aircraft then helped direct the fighters toward an incoming strike.
Notable Point · 20:45-22:39
Understand why a four-fighter patrol needs eighteen aircraft
A continuous four-fighter combat air patrol requires alert aircraft, relief cycles, and maintenance reserves far beyond the number currently airborne.