In the 1930s, neither the Army nor the Navy had a device that could adequately identify targets on the ground, sea, or in the air. Identifying friendly planes returning to carriers under poor visibility was an especially serious problem. To solve the problem, NRL sought solutions through the use of radio waves.

Radio recognition IFF system

The first radio recognition IFF system in the U.S., Model XAE (1937). The airborne equipment, developed at NRL, is shown at the top. The shipboard equipment is shown below. When in the vicinity of friendly ships, the aircraft equipment transmitted a series of coded signals. Aboard ship, the Yagi antenna gun shaped equipment was pointed at the aircraft, to flash.

  • In 1937, NRL developed the first U.S. radio recognition identification friend-or-foe (IFF) system, the Model XAE, which met an urgent operational requirement to allow discrimination of friendly units from enemy units.
  • The Mark X IFF was a later radar beacon system developed by NRL. It was essential to the military because it reduced fratricide when used with beyond-visual-range weapons.
  • By 1958, the FAA had established the Air Traffic Control Radar Beacon System (ATCRBS), which is essentially the civilian version of the Mark X. The International Civil Air Organization later adopted the ATCRBS, making the Mark X the basis of the world's air traffic control system.
  • In 1960, the Mark XII IFF system was developed. It was the first IFF system to use cryptographic techniques to prevent deception where an enemy appears as a friend by using a captured transponder.