Huff-Duff

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High Frequency Direction Finder is usually known by its acronym HF/DF, pronounced Huff-Duff. This has become the common name for this type of equipment, and was coined during World War II.

Huff Duff is part of the armoury of the analysis of radio transmissions, known as ELINT. It is the sister discipline to the analysis of messages COMINT.

Battle of the Atlantic

Along with ASDIC (sonar), Ultra code breaking (SIGINT) and radar, "Huff-Duff" was a valuable part of the Allies armoury in detecting German U-boats and commerce raiders during the Battle of the Atlantic.

The idea of using two or more radio receivers to find the bearings of a radio transmitter and with the use of simple triangulation find the approximate position of the transmitter had been known and used for years. The Royal Navy was the first to design an apparatus that could take bearings on the high frequency radio transmitters employed by the German Kriegsmarine in World War II.

Many shore based installations were constructed around the North Atlantic and when ever a U-boat transmitted a message "Huff-Duff" could get bearings on the approximate position of the boat. Because it worked on the electronic emission and not the content of the message it did not matter that the content was encrypted using an Enigma machine.

In 1942 the allies began to install Huff-Duff on convoy escort ships, enabling them to get much more accurate triangulation fixes on U-boats transmitting from over the horizon, beyond the range of radar. This allowed hunter-killer ships and aircraft to be dispatched at high speed in the direction of the U-boat, which could be illuminated by radar if still on the surface and ASDIC if it had dived.

Battle of Britain

In the Battle of Britain, "Huff-Duff" was the mechanism used by the RAF to track the location of their fighter squadrons in the air. RAF fighters had a HF channel of their radios set to broadcast a signal for fourteen seconds of every minute. A clockwork mechanism regulated this broadcast, which was codenamed "Pipsqueak".

Each Fighter Command sector had HF/DF receiving stations that would monitor the Pipsqueak broadcasts and telephone the bearings back to the sector control rooms where they could be triangulated and the squadron's location plotted.

References

"Secret Weapon: U.S. High-Frequency Direction Finding in the Battle of the Atlantic" by Kathleen Broome Williams, Naval Inst Pr (October 1, 1996), ISBN 1557509352

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