From: A rare 1944 edition of the Kurzsignalheft, or "Enigma Code Book" German, circa 1944

During the Second World War the German U-boats used Kurzsignale or Short Signals to send their messages. The Kurzsignale were an important part of the complex Kriegsmarine communications system. In general, the Kurzsignale were four letter groups representing all kinds of sentences regarding tactical information such as course, enemy reports, position grids or weather reports.

An important reason for the Kriegsmarine to apply these Kurzsignale was the Allied use of High Frequency Direction Finding, also called HFDF or Huff Duff. This system enabled Allied Forces to accurately determine the position of German transmissions. This was an important tactical advantage in the Atlantic, revealing the positions of German ships and U-boats. The use of Kurzsignale decreased the length of the Morse messages enormously, often reducing broadcasting time to less then one minute. This way, the German Navy made it harder to fix positions with Huff Duff.