High Frequency Direction Finder is usually known by its acronym HF/DF pronounced Huff-Duff which 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 and is known as ELINT. It is the sister discipline to the analysis of messages SIGINT.

World War II

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 Enigma.

In 1942 the allies began to install Huff-Duff on convoy escort ships. This allowed them to get a much more accurate triangulation fix on over the horizon radio transmitting U-boats. As radar could not look over the horizon, 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.

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