The US and Canada are surrounded by an Air Defense Identification Zone (ADIZ) in North America. Under the auspices of the North American Aerospace Defense Command or NORAD, it is jointly administered by the civilian air traffic control authorities and the militaries of both nations. The Canadian ADIZ when discussed separately is known as the CADIZ. On any day given, there are about 2,500 aircraft that fly into the Air Defense Identification Zone of both Canada and the United States. That ADIZ is located about 200 miles from the shore and is intended to give plenty of time to detect the aircraft and determine its identity.
North Korea launched an invasion of South Korea on June 25, 1950, drawing the United States into a war that would last for three years. The Joint Chiefs of Staff ordered Air Force air defense forces to a special alert status believing that the North Korean attack could represent the first phase of a Soviet-inspired general war. The Air Force uncovered major weaknesses in the coordination of defensive units to defend the nation’s airspace in the process of placing forces on heightened alert. As a result, Air Defense Identification Zones (ADIZ) were staked out along the nation’s frontiers and an air defense command and control structure began to develop. Unidentified aircraft approaching North American airspace would be interrogated by radio with the establishment of ADIZ. the Air Force launched interceptor aircraft to identify the intruder visually if the radio interrogation failed to identify the aircraft. In addition, the Air Force received Army cooperation. As part of a coordinated defense in the event of attack, the commander of the Army’s Antiaircraft Artillery Command allowed the Air Force to take operational control of the gun batteries.
Which is almost exclusively over water, the joint US/Canadian ADIZ, serves as a national defense boundary for aerial incursions. Any aircraft that wishes to fly in or through the boundary must file either an Instrument Flight Rules (IFR) flight plan or Defense Visual Flight Rules (DVFR) flight plan before crossing the ADIZ (14 CFR 99.11). Aircraft must have an operational radar transponder and maintain two-way radio contact (see 14 CFR 99.9 & 99.13) while approaching and crossing the North American ADIZ. In the US, the FAA handles the requests of international aircraft and Transport Canada handles Canadian requests.