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Leontine Theresa "Lona" Cohen  (January 11, 1913 – December 23, 1992), also known while she was in London as Helen Kroger, was an American spy for the Soviet Union. She was the wife of another spy, Morris Cohen.
Leontine "Lona" Cohen was born in Adams, Massachusetts. An American citizen, she was a member of the Communist Party USA and had been recruited into Soviet espionage in 1939 by her husband, Morris. She worked for Soviet case officers, including Anatoli Yatskov, out of the New York Rezidentura during World War II.
After her husband was drafted in 1942, Cohen ran a network that included engineers and technicians at munitions and aviation plants in the New York area. One of her sources smuggled a working model of a new machine gun out of a munition plant. She worked at two defense plants, the Public Metal Company in New York City in 1941 and the Aircraft Screw Products plant on Long Island in 1943.
She was a courier who picked up reports from Theodore Hall, and a source cover named "FOGEL" and "PERS" from the American secret atomic weapons project at Los Alamos, New Mexico and carried them to the Soviet consulate in New York, where a KGB sub-residency under a young engineer, Leonid R. Kvasnikov, coordinated operations and dispatched intelligence to Moscow.
After the defections of Elizabeth Bentley and Igor Gouzenko, the Cohens ended contact with Soviet intelligence until 1949, at which time they began working with Col. Rudolph Abel, a U.S. based illegal resident. After Fuchs was arrested in Great Britain in 1950, Cohen and her husband fled to Moscow, where she received additional training as a radio operator and cipher clerk. In 1954, the pair resurfaced in London under the names Helen and Peter Kroger with New Zealand passports. They set up an antiquarian book business which was cover for their activities of running the London Illegal Rezidentura. Gordon Lonsdale worked with them as part of the Portland Spy Ring.
Whilst in London, the Cohens were friends with Frank and Nora Doel. Frank Doel is the bookseller whose correspondence with the author Helene Hanff became the bestseller, 84 Charing Cross Road. In her follow-up book, The Duchess of Bloomsbury Street, Hanff reported an anecdote told her by Nora Doel. One New Year's Eve, the Doels gave a party at which Lona Cohen (aka Helen Kroger)
arrived looking very exotic in a long black evening dress. 'Helen, you look like a Russian spy!' said Nora. And Helen laughed and Peter laughed and a few months later Nora picked up the morning paper and discovered that Helen and Peter Kruger were Russian spies
In the basement of their house, at 45 Cranley Drive, Ruislip, situated not far from the military airfield of Northolt, they set up a high speed radio transmitter and began sending Moscow “information of special importance”. In January 1961, they were arrested for espionage, and in March, she received a sentence of 20 years while her husband got 25 years, of which they served only eight.
Before being taken in custody, Mrs. Kroger asked permission to stoke up the boiler. Before she could do so, Detective Smith, a veteran “spy catcher” who was in charge of the arrest, insisted on checking her handbag first. It was found to contain microdots, the photographic reduction of documents, in order to make them small enough to be smuggled out of the country more easily. In 1969, the two were finally exchanged with the Soviet Union for a British subject called Gerald Brooke. Back in Moscow, they continued training colleagues for illegal intelligence operations.
Later life 
Fictional portrayals 
In 1983, British playwright Hugh Whitemore dramatized the case as Pack of Lies, which was performed in London’s West End theatre district starring Judi Dench and Michael Williams. It played on Broadway for 3½ months in 1985, for which Rosemary Harris won the best actress Tony award for her portrayal of the British neighbor of the Cohens ("Krogers").
It was made into a TV movie starring Ellen Burstyn, Alan Bates and Teri Garr (the last playing "Helen Schaefer", i.e., "Helen Kroger", i.e., Lona Cohen) which aired in the U.S. as a Hallmark Hall of Fame presentation in 1987 on CBS. The story centred on the seemingly pleasant and ordinary neighbours and friends, the Search family, whose home was eventually used as a base to spy on the Schaefers (i.e. "Krogers").
- The Independent article on Cohen
- Hanff, Helene (1976). The Duchess of Bloomsbury Street. Avon. p. 40. ISBN 0-380-00634-0. More than one of
- BBC report on the case. Includes a video news report on the Krogers/Cohens' return to the Soviet Union and an interview with former Foreign Secretary George Brown over the issues.
- Russian Foreign Intelligence Service (SVR) (in Russian)
- Interview with Dr. Svetlana Chervonnaya.
- FBI Morris and Lona Cohen file, 100–406659
- Rebecca West, The New Meaning of Treason, New York: Viking (1964), pp. 281–88
- Joseph Albright and Marcia Kunstel, Bombshell: The Secret Story of America's Unknown Atomic Spy Conspiracy, New York: Times Books (1997) pp. 244–53
- Russian Federal Foreign Intelligence Service, Veterany vneshnei razvedki Rosii (Veterans of Russian foreign intelligence service), Moscow: Russian Federal Foreign Intelligence Service, (1995).
- John Earl Haynes and Harvey Klehr, Venona: Decoding Soviet Espionage in America, New Haven: Yale University Press, 1999, pp. 316, 317–319, 320, 321, 334 (ISBN 0-300-08462-5)
- Richard C.S. Trahair and Robert Miller, Encyclopedia of Cold War Espionage, Spies, and Secret Operations, New York: Enigma Books (2009), ISBN 978-1-929631-75-9
- Ruislip Online page on the Krogers. Includes comments from friends and neighbours and a picture of the bungalow lived in by them. Very detailed local information.