During World War II, each service used its own method to designate its electronic radar/tracking systems. For example, Army radars were classified under the initials SCR, which stood for �Signal Corps Radio.� Different designations for similar systems confused manufacturers and complicated electronics procurement. In February 1943, a universal classification system was implemented for all services to follow, ending the confusion. To indicate that an electronic system designation followed the new universal classification, the letters �AN,� for Army-Navy, were placed ahead of a three-letter code. The first letter of the three-letter code denoted the type of platform hosting the electronic device, for example: A=Aircraft; C=Air transportable (letter no longer used starting in the 1950s); F=Fixed permanent land-based; G=General ground use; M=Ground mobile; S=Ship-mounted; T=Ground transportable. The second letter indicated the type of device, for example: P=Radar (pulsed); Q=Sonar; R=Radio. The third letter indicated the function of the radar system device, for example: G=Fire control; R=Receiving (passive detection); S=Search; T=Transmitting. Thus an AN/FPS-20 represented the twentieth design of an Army-Navy �Fixed, Radar, Search� electronic device.

Originally, "AN" did stand for "Army-Navy"; later, though, after the Air Force came along, it became just a 'designator' of military equipment.