Operating under at least five different names in the course of her career, Ursula Kuczynski was a singularly accomplished intelligence agent whose espionage activities spanned some fifteen years, from 1931 to 1946. Deployed by the Soviet military intelligence service GRU, she won recognition as one of the greatest female secret agents of the twentieth century, operating espionage rings in China, Poland, Switzerland, and Britain. At the height of her career in 1942–1943 she radioed to Moscow invaluable data for constructing an atomic bomb derived from the nuclear physicist Klaus Fuchs and others she controlled as an agent in England.

Kuczynski was evidently skilled at evading detection, escaping from close brushes with counterintelligence operatives. Not so Klaus Fuchs, who was caught and imprisoned in Britain for nine and a half years, or Richard Sorge, the master spy who had recruited her for the Soviet military intelligence apparatus and was also caught. Sorge, from whom Kuczynski acquired her code name, Sonja, in 1933, was executed in Japan after warning Moscow in May 1941 (in vain) of Hitler’s forthcoming invasion of the Soviet Union.

Ursula Maria Kuczynski was born on May 15, 1907, in Berlin, one of six children of Robert Rene (1876–1947) and Berta Kuczynski. Her father, a distinguished economist who specialized in demography and labor statistics, taught and worked in Germany, the United States, and Britain. (Ursula herself stayed in Philadelphia and New York for the year 1928-1929.) Though wealthy, the Kuczynskis were considered “progressive” and later five of the six children joined the Communist Party.

Ursula grew up in a large lakeside villa on Schlachtensee in the borough of Zehlendorf. Early on drawn to the Communist movement, she joined the party’s youth group in 1924, took part in Berlin’s street demonstrations, and became a full party member at the age of eighteen, upon which she was dismissed by her employer, the Ullstein Verlag publishing house.

Soon after this Kuczynski met and married Rolf Hamburger, an architect and a leftist. She founded a Marxist Workers Library and started writing for the party newspaper, Rote Fahne (Red Flag). In 1930 she and her husband moved to China, having been told by the Communist Party that she would be “connected” in Shanghai.

With Rolf Hamburger employed as an architect, the couple began a pleasant bourgeois life, but Kuczynski was waiting impatiently for a contact with communists. It took four months and a friendship with Agnes Smedley, an American leftist journalist, to make a connection. Smedley introduced Kuczynski to Richard Sorge, who like Smedley worked for the German press. He was thirty-five and for a year had already been the “rezident” agent in Shanghai of the Glavnoe Razvedivatlenoe Upravlenie—GRU—the Chief Intelligence Administration of the Red Army.

Sorge asked Kuczynski whether she was ready to face danger. She agreed to make space available for his clandestine meetings—altogether eighty in number—with Chinese communists, the chief interest of Moscow at that juncture. She joined his ring and, without her husband’s knowledge, stored their weapons, hid a Chinese comrade who was on the run, and learned some Chinese. In 1931, in the midst of this clandestine work, she bore a son, Michael. Her marriage to Rolf Hamburger fell apart, but she remained with him. He later became a communist. As Japan began infringing on Chinese territory, Kuczynski became one of Sorge’s most active informants. She also wrote long articles for Rote Fahne.

Two years later, Sorge telephoned Kuczynski and said he was leaving China, without seeing her, but wished her well. Later she learned he had gone to Moscow and recommended her to the GRU. His Shanghai deputies inquired whether she was willing to go to Moscow for training, but without her two-year-old son. “I agreed,” she wrote in her autobiography. She left her son with in-laws in Czechoslovakia.

At Red Army headquarters in Moscow’s Arbat district, Kuczynski met her new chiefs, who addressed her by her code name, Sonja. In the GRU school on the eastern outskirts of Moscow she was one of seven students learning how to build radio transmitters and receivers, Morse code, and Russian. She was allowed to write to her in-laws once a month. Much later she reflected that to be a communist was always to be in company and that it was “sometimes difficult never to be alone.”

Her training complete, Kuczynski was assigned in February 1934 to Mukden in the heart of turbulent Manchuria, which had been seized from China by the Japanese. Her superior was to be “Ernst,” a former German sailor, with whom she had been in radio school in Moscow for a fortnight. She told him she had a three-year-old son. He thought a minute and replied, “What should I have against a child? We need a new generation.” She proceeded to Prague to fetch her son, who was “alienated,” she wrote, having been away from her for seven months, then joined Ernst in Trieste and sailed for China, stopping in Shanghai to see Rolf Hamburger before taking the train to Mukden. As cover for her new liaison work with underground Chinese communists, Kuczynski opened the Manchoukuo Book Agency, Manchoukuo being the Japanese designation for Manchuria.

Chinese partisans were already sabotaging Japanese railways. “Our transmitter was the link between the partisans and the Soviet Union,” Kuczynski wrote. She transmitted twice a week, sometimes 500 groups of coded material. Each group had five numbers. She bought and transported large quantities of ammonium nitrate, sulfur, and other chemicals for explosives for the partisans. She also learned 600 Chinese characters and 1000 spoken words.

In April 1935 one of their main Chinese communist contacts was arrested and his group dispersed. Moscow ordered Sonja and Ernst to break off all contact with partisans and quit Mukden. Traveling to Beijing Kuczynski found she was pregnant, this time by Ernst. Just then a comrade who could implicate them was arrested by Chinese intelligence agents. The couple fled.

Back in Moscow Kuczynski’s control officer offered and she accepted Poland, this time with Rolf Hamburger. She stopped off in London for a reunion with her parents and all her siblings, who had sought asylum there. In Warsaw, she built her transmitter in a phonograph box and was delighted when it instantly functioned. She transmitted mostly material on the Polish economy and politics. Learning Polish, she forgot her smattering of Chinese. Rolf again found work as an architect. Kuczynski's daughter Janina, by Ernst, was born in April 1936.

Soon after the Germans took over the free city of Danzig in September 1939, Kuczynski was dispatched to advise German communists stranded there. She had a close brush with a German official who heard her through a wall transmitting Morse. But in Danzig she also received a signal that “The People’s Commissariat for Defense has decided to award you the Order of the Red Banner.”

Back in Warsaw, Kuczynski's GRU superior, Colonel Tumanyan, whom she knew as "Andrei," stopped by and noted that she was not her old “frolicsome” self. She told him of her personal situation with Rolf and Ernst, saying that she missed Ernst but did not want to go back to him. Andrei recommended more training in newer radio transmitters in Moscow. She went there in June 1937, again leaving her two small children with her in-laws.

In Moscow Kuczynski learned how to make explosives and to build a newer transmitter model. She was also invited to the Kremlin to receive the Red Banner order from President Mikhail I. Kalinin. It was the time of Stalin’s great purges, which swept away some of her comrades. Still not disillusioned with Stalin, she wrote of that time: “I was convinced that they (the comrades) must have made mistakes.”

Kuczynski was sent to Switzerland in late 1938 to set up a new spy ring, again with Rolf, who soon left for the Far East. In February 1939 she met Len Beurton, an English communist who had fought bravely in Spain with the international brigades. For him it was “love at first sight; she had a very good figure.” It took longer for her.

From Switzerland, Ursula Kuczynski's team established contacts in Germany and informed the Soviet Army of German military and industrial developments. At one time Beurton and his associate Allan Foote staked out a restaurant that Hitler regularly frequented and planned an assassination attempt.

The GRU authorized a marriage to Len Beurton, through which Kuczynski became British. They were married on February 23, 1940, the Day of the Red Army. Ernst visited once and saw his daughter Janina for the first and only time. At the end of 1940 Moscow ordered Len and Ursula to England. It took months to get there by way of neutral Portugal and not until May 1941 was Kuczynski able to make a rendezvous in London with “Sergei,” her new Red Army control.

In England Kuczynski met Fuchs, like herself a German political exile, through a younger sister, Brigitte Kuczynski, in late 1941. She had already begun clandestine transmissions to Moscow from a set she had built in her rented house near Oxford. Fuchs was working at the secret British atomic research facility at nearby Harwell. They bicycled into the countryside for their meetings and he handed over written material in minuscule script, either copies of his own work or the work of others that he had memorized and, sometimes, questions for Moscow. She told an interviewer in 1990 that she looked at some of the material out of curiosity and found it was “like hieroglyphics for a layman that I couldn’t begin to comprehend.” They talked about war and politics, but as a precaution their meetings never lasted more than thirty minutes. “It was a great relief for him to have someone he could talk to openly.” She called Fuchs “a good, a decent man.” She continued to meet with him through 1943, when she was in the final months of pregnancy, and also just after her second son, Peter, was born in September.

In addition to Fuchs, Kuczynski was running other agents, including a Royal Air Force officer, a specialist in submarine radar, Germans working for the American Office of Strategic Services, and a senior secretary of chemists working on plutonium production. She sent analysis and information from her brother Jürgen, who was hired by the U.S. Army’s Bureau for American Bombing Strategy, and even her father. In 1943 she was told by “Sergei,” her Soviet contact in London, that the chief of GRU had said, “If we had five Sonyas in England the war would end sooner.”

Still observing the iron rules of conspiracy in her autobiography (completed in 1974 and published in East Berlin three years later under the title Sonjas Rapport), Kuczynski never mentioned Fuchs, who was still alive. But she did write about Sorge and many other clandestine operatives. Only years later did she discuss Fuchs openly with visitors, and in an expanded English autobiography published in 1991, Sonya's Report.

Moscow broke off contact with Kuczynski in the summer of 1946, with no explanation. “I wasn’t bitter,” she recalled. “I didn’t see the work as a means to learn a living, but as the activity of a communist.” Still, her cover was nearly broken, she suspected, by Allan Foote, who had been a clandestine agent with her in Switzerland and then confessed all to British intelligence shortly after the war. In 1947 two men knocked on her door and one said: “You were a Soviet agent for a long time. We know you were not active in England. We’re not here to arrest you but to ask your cooperation.” “How would you like a cup of tea?” she coolly responded. She turned aside further questions. They were satisfied and left.

In March 1950, still in England, Kuczynski found a coded message at a pre-arranged site under a tree saying she could go to East Berlin. She buried her radio, bought four U.S. Army duffel bags, and took Janina and Peter with her to West Berlin, proceeding by elevated train to the Soviet Sector. The few hotels were full, so she rented a room from an old couple and spent her first night in the city of her birth in a damp bed; the first night as a spy in from the cold was cold in unheated East Berlin. Soviet comrades found her proper housing and arranged for a job for her. Len and her son Michael joined them in 1951.

Twice awarded the order of the Red Banner, the highest Soviet military decoration, Kuczynski also held the rank of colonel in the Red Army. Her only connection with the GRU after settling in East Berlin was in 1969 when she was invited to a ceremony to receive her second Red Banner decoration.

Turning to writing, Kuczynski gained popularity as a writer including stories for children and young adults. She wrote a biography of Olga Benario, a German communist she had known who was gassed by the Nazis in 1942, and her autobiography. One of the stories in her collection “Der Gong des Porzellanhändlers,” “Die Acht — rückwärts,” tells how she was denied a driving license because of growing anti-Jewish sentiment.

Ursula Kuczynski died in Berlin on July 7, 2000, aged ninety-three, survived by her three children, five grandchildren, and four sisters.