Berlin where she married her first husband, Rudolf Hamburger, who was an architect and fellow member of the Communist Party. It was also at this time that she set up the Marxist Workers' Library (MAB) in Berlin. She headed up the MAB between August 1929 and June 1930. Espionage China With her husband she relocated, in July 1930, to Shanghai where a frenetic construction boom afforded ample opportunities for Hamburger's architectural work. She would remain based in China till 1935. It was here that the couple's son, the Shakespeare scholar Maik Hamburger, was born in February 1931. After they had been in Shanghai for a little more than four months she was introduced by the US journalist Agnes Smedley to another German expatriate, Richard Sorge, outwardly a journalist, who is better remembered as "Ramsai", an active agent of the Soviet Intelligence Directorate (GRU). Sources are vague as to whether the Hamburgers were already working for the GRU before they left Germany for China, but in any case it was after the meeting with Sorge that between 1930 and 1935 "Sonja" (the cover name by which Kuczynski was known in The Service) operated a Russian spy ring under Sorge's direction. In Autumn 1931 she had to send her son Maik to live with her husband's parents (now relocated from Germany to Czechoslovakia) when she was sent to Moscow where she undertook a seven-month training session before returning to China. There had been a concern that if baby Michael had accompanied her to Moscow he might inadvertently have blown her cover later by blurting out words in Russian. It was also during this period that she mastered various practical aspects of spy-craft. This included radio operator skills that were much prized in the world of espionage: she learned to build and operate a radio receiver, becoming an exceptionally capable and accurate user of Morse code. Between March and December 1934 she was based in Shenyang in Manchuria which had been under Japanese military occupation since 1931. Here she met the GRU's chief agent who was working under the name "Ernst". Sonja and Ernst had a romance which would result in the birth of her daughter Janina in April 1936. Her husband Rudolf Hamburger generously acknowledged "Nina" as though she were his own daughter. The GRU was nevertheless concerned that the affair with Ernst might lead to the unmasking of both agents, and