Document created: 4 September 03
Air & Space Power Journal - Fall 2003

Swedish Signal Intelligence, 1900–1945 by C. G. McKay and Bengt Beckman. Frank Cass Publishers (http://www.frankcass.com), 5824 NE Hassalo Street, Portland, Oregon 97213-3644, 2002, 310 pages, $49.50 (hardcover).

Signals intelligence (SIGINT) is seldom covered in historical texts, which makes McKay and Beckman’s first authoritative account of Sweden’s SIGINT both valuable and unique. It is published in English and charts the path of a neutral Sweden as it sought to keep a fine balance between the Russians and Germans in World War I and the Allies and Germans in World War II. The authors are to be commended for their detailed, up-front explanation of SIGINT: how radio and telegraph coding was used between various countries and their diplomatic missions, what kinds of transmissions third parties could intercept, and the numerous tasks involved in decoding that data.

As an integral part of the book, the authors documented Sweden’s ties to Finnish independence groups in 1917 and its associations with the independent Baltic states of Estonia, Latvia, and Lithuania prior to their conquest by the Soviet Union in 1939. Those conquests and the 1939 Winter War in Finland brought home to the Swedes the threat they faced from an expanding Soviet Union. The Swedes reorganized their military repeatedly during the interwar years in response to potential adversaries and developed a SIGINT organization that would serve it well during World War II.

The outbreak of World War II and the German occupation of Denmark and Norway made the Swedish position of neutrality more precarious. Soviet codes were difficult at first but were eventually mastered; the German Enigma keys were even harder to break. German landline communications ran through Swedish territory and could be monitored and exploited. That opportunity allowed the Swedes to eventually break the encryption codes used by the German Geheimschreiber teleprinter. That successful work on its simultaneous machine encryption required both an understanding of codes and electro-mechanics. With a staff of fewer than 400 people, the Swedes achieved impressive results: Soviet, German, and American codes were broken, and Swedish code security was monitored and corrected when necessary. Interestingly, while the Germans realized that the integrity of their communications crossing Sweden had been compromised, their own bureaucratic bungling prevented any improvement in their signal security.

After demonstrating its value, SIGINT was removed from the Swedish general staff’s signal section in 1942 and established as an independent authority. It not only broke codes but also monitored illegal radio transmissions inside Sweden, leading to the apprehension of spies. This became an early vision of a unified SIGINT establishment.

In 1944 when the Finns were required to remove German forces to comply with Soviet armistice demands, the Swedes proposed that a network of agents stay behind to keep Sweden informed of Soviet operations inside Finland. While this network was never emplaced, Finnish SIGINT equipment, codes, and intelligence documents were brought to Sweden that year. That material was exploited and retained until it was destroyed in the 1980s to maintain the secrecy of those activities.

The neutral capital of Stockholm offered numerous SIGINT interception opportunities as exemplified by the Oslo-Berlin communications. Those interceptions provided the Swedes with insight into German operations and diplomatic traffic. Other interesting tidbits in the book cover the possible compromise of Operation Overlord, British counterintelligence operations inside the Swedish Embassy in London, and the role played by the Hagelin Crypto Machine Company. Among the smaller neutral nations of World War II, Sweden was the most ready to tackle SIGINT challenges at the beginning of the Cold War, and may have come closest to matching the British successes of Bletchley Park.

While a more complete book could have included the Cold War history of Swedish SIGINT (which would be interesting and possibly answer many Baltic mysteries), SIGINT books are rare, and this one is a must-read for intelligence professionals. The detailed explanation of cryptology, coding, and the way SIGINT is produced puts this book ahead of other, more technical, texts. Historians interested in World War II may even have to reconsider some events of that war after reading this book.

Capt Gilles Van Nederveen, USAF, Retired
Alexandria, Virginia

Disclaimer

The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.