It was vital to MI5 to make the communications sent by double agents to Germany as convincing as possible. At first Treasure sent messages to Kliemann in secret ink or encoded letters, but later she used a radio transmitter set. She passed to him false information concocted by MI5 as part of an elaborate and successful deception plan to keep D-Day secret. Treasure led Kliemann to believe that there were very few troops in South West England and that she had a boyfriend in the 14th Army (a non-existent unit invented by the Allies). This information fitted in with messages from other double agents and supported the Germans’ false belief that the Allies would land at Calais rather than in Normandy. In this letter the deputy head of the Government Code and Cypher School thanks Sergueiew and her colleagues for helping to break codes and deceive the enemy.