A concealable, body-worn direction finder used by German forces to find clandestine radios operating during World War II.
With resistance cells and secret agents deployed throughout Nazi-occupied Europe, anyone with a shortwave radio could tune in to hear coded message transmissions being sent back and forth across the continent. Both the German Abwehr and Gestapo worked hard to locate these radio operators as soon as they went on the air. Because of the lack of automobiles on the roads through most of Europe, resistance lookouts could quickly spot a signals intelligence vehicle entering the area, meaning the Germans had to find a way to get direction-finding equipment into a neighborhood or city block without alerting anyone. This device, called a Gürtelpeiler was developed in 1942, and manufactured by the Kapsch company in Austria. (Photos via cryptomuseum.com). It was designed to fit the natural curve of the body, and the large loop around the neck functioned as an antenna. Previous direction finders had fit inside of a suitcase, but the Gürtelpeiler was the most concealable model yet. The maximum range was 3 kilometers, but it functioned best within one kilometer of the radio. This incredibly forward-thinking, body-worn design was adapted into several other models used throughout the Cold War. Larger fixed direction finders were always searching for secret transmissions, and directed mobile teams towards the radio, where they would begin sweeping a particular region. Once the operators had narrowed the search to a single city block or row of houses for example, German troops would move in and conduct house-to-house searches to find the radio operators. The only real defense against a direction finder was limiting transmissions to the shortest times possible. But sending encoded messages via Morse code was time-intensive no matter what. Secret radio operations in occupied Europe was incredibly dangerous work, and operators generally had a one-month lifespan once they deployed.