The Kriegsmarine was the German navy of WWII. The main signal intelligence agency of the Kriegsmarine was the so called B-Dienst (observation service), which was responsible for attacking Allied naval cryptographical systems. The B-Dienst started their work already during the interwar years, with their primary target being the British Royal Navy. The Royal Navy used the following systems at the start of the war:Naval Cypher No1, a 4-figure book used since 1934.