Direction findung systems were used in the Swiss Army for various purposes. On one hand in the signal intelligence (SIGINT), on the other hand for aircraft location and assistance during the landing approach by the Air Force.

In the first years, the direction finding equipment was given simple abbreviations, usually two letters, so LP stands for the Langwellen Peiler (Longwave DF). According to the new naming scheme, which was introduced in 1951, direction finding systems got designations P-7xx, followed by a two-digit number.

The information about the direction finding systems and the background of their military use are sparse. I am always thankful for additional information, technical documents and operating instructions,photographs of DF installations and would even have some space for one or another direction finding receiver in my collection

Direction finding systems were used for various purposes.

On the one hand, the Monitoring service used direction finding to detect suspicious foreign signals, in WWII especially those operating in Germany, or signals from within the country which could originate from spy radio stations. Near-field direction finding was carried out after a rough localisation of the transmission with direction finding vehicles, which could approach a suspicious transmitter site as inconspicuously as possible in the neighbourhood. Direction finding receivers carried inconspicuously by the defence signalmen could then be used to determine the location between or within individual buildings.

On the other hand, direction finding was used by the air force to localise aircraft, they were used in permanent installations and at military airfields, where direction finders were mounted in vehicles.

• Funkpeilung - Die Geräte und Anlagen der Schweizer Armee bis 1945, Eduard Willi, HB9YQ