IFF MK III - IDENTIFICATION OF FRIEND OR FOE [Main Title]

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  • Title: IFF MK III - IDENTIFICATION OF FRIEND OR FOE [Main Title]
  • Film Number: AMY 171
  • Other titles:
  • Summary: A very technical training film that describes the major components that form the IFF mk 3 unit, and how it is necessary to combine it with the Chain Home radar system for effective operation. It is the modern equivalent of the challenge and secret password. Good use is made of schematic diagrams, together with clear photography linked together by a lucid commentary.
  • Description: Film opens with sentry/guard asking for the password of an intruder he has detected, the correct password in given and the intruder allowed forward. For the past one thousand years the password has been the only way of detecting friend from foe, and with the advent of mechanisation and in particular, aircraft, a system of challenge is necessary to supplement the Chain High (CH) and Chain Low (CL) radars network that can detect but not identify a target. Film cuts to WAAFS at a plotting table collating the information received from the CH and CL radar stations which is collated and passed via the control centre to fighter pilots, anti aircraft gun and searchlight crews. Because information is needed about the intruder before sight or sound contact is made a device employing radio waves must be used. Film cuts to an aircraft fitted with a transponder incorporating a radio receiver/transmitter that responds to a signal transmitted by the ground IFF station. Cut to IFF transmitting mast, and the operator inside the station. Hostile aircraft do not respond to the challenge or transmit the wrong signal. It became apparent that the IFF system must be closely integrated with the CL and CH radars, the single cathode ray monitor displaying both IFF and radar responses, without mutual interference, or impairing the radar performance and must not be easily jammed by the Germans. This was achieved by allocating the IFF a frequency band of its own. A suitable band was determined by technicians at the Royal Aircraft Establishment and after a series of trials, the 157 to 187 mHz band was selected. Additionally, to ensure compatibility with the ASV mk 2, (Air to surface vessel radar) operating at 176 MHz was required. The film cuts to show examples of the components of the IFF mk 3 system both on the ground and in the air. In use the IFF mk 3 transmitter radiates pulses continuously, when the aircraft is within the range of the interrogator and has therefore has received its challenge, the transponder automatically answers and shows the aircraft to be friendly. This equipment may also be fitted to tanks, aircraft and naval ships. Examples of each type of installation are shown. Reel two: Because the film has been produced as an aid to technical training for the IFF mk 3, it now proceeds in extreme detail, aided by static and animated diagrams with close up photography, to explain some of the additional features necessary to fully integrate the system with the CH radar. These include continuous sweeping over the IFF frequency band of 157 to 187 mHz; the ability to alter the character of the signal transmitted by the aircraft transponder; the IFF system to have the same geographical range as the CH radar; at the ground station a special interface to integrate the IFF and radar responses for display on a large circular calibrated screen. Cut to IFF mast and hut where a WAAF is seen operating type 7A console incorporating the circular screen with the ability to manually rotate the circular scale and/or the rotating the two part antenna (outside the hut) to enhance discrimination. This ‘Split’ technique is also a very effective way of direction finding a signal. Security is a problem. Explosive charges are built into the transponder should it fall to the enemy. The signal from the transponder may be coded by transmitting three different pulse widths, giving six selectable combinations for the transponder. The selected combination is displayed on the 7A console where the operator can compare it with the code of the day given in Orders. The third pulse, of the greatest width, is reserved as a distress signal for an aircraft simultaneously transmitting SOS by radio. The film concludes the IFF mk 3 is not perfect, and can be difficult to use during raids of high aircraft density, but may be regarded as the modern equivalent of the challenge and secret password.
  • Alternative Title:
  • Colour: B&W
  • Digitised:
  • Object_Number: AMY 171
  • Sound: Sound
  • Access Conditions:
  • Featured Period: 1939-1945
  • Production Date: 1943
  • Production Country: GB
  • Production Details: ROYAL AIR FORCE (Production sponsor) Science Films (Production company) ROYAL AIRCRAFT ESTABLISHMENT (Production company)
  • Personalities, Units and Organisations:
  • Keywords:
  • Physical Characteristics: Colour format: B&W Sound format: Sound
  • Technical Details: Format: 35mm Number of items/reels/tapes: 2 Length: 1990ft
  • HD Media:
  • Link to IWM Collections page:

    AMY 171

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