IFF secondary radar standards
Surface Radars Ground Based Defence Radars - Naval Defence Radars

Primary radar had its heyday during the Second World War, both on land and at sea. It soon became necessary to distinguish between friendly and aggressive radar plots. The Allies therefore developed equipment that transmitted a signal to indicate that the aircraft was friendly. This system was exaggeratedly called IFF (Identification Friend or Foe) in the sense that it did not detect enemies directly.

As in the case of civil air cover, the need for standardization arose between the various countries cooperating within common armed forces.