Trying to Make the MAGIC Last: American Diplomatic Codebreaking in the Early Cold War

Abstract

No reader of this journal needs to be reminded of the importance of communications intelligence (Comint) in the history of the Second World War.1 No account of the war can now be deemed complete without reference to the work of Allied and (to a lesser extent) Axis codebreakers. Indeed, as communications intelligence has moved out of the shadows of history, scholars, who in the past remained blissfully unaware of (or uninterested in) the role of communications intelligence, now must resist the temptation to exaggerate its contributions and to consider the decryption files an evidentiary Aladdin's Cave from which the diligent researcher can expect to extract riches illuminating every aspect of the war. One does not have to be the president of the “Ultra Won the War” Club to acknowledge the centrality of codebreaking in the American intelligence effort during World War II. After Pearl Harbor, the Army and the Navy divided the communications intelligence effort, with the former focusing on foreign army and diplomatic communications and the latter concentrating on foreign naval radio traffic. The briefest glimpse at the U.S. Army's Comint program suggests the scale of the achievement. In the summer of 1939, as the world edged closer to the precipice of war, the roster of the Signal Intelligence Service (the unit in the Signal Corps responsible for intercepting and decrypting the diplomatic communications of foreign governments) numbered scarcely two dozen individuals who, from a suite of cramped rooms in the Munitions Building in downtown Washington, DC, labored with mixed results against the codes and ciphers of four governments: Germany, Italy, Japan, and Mexico. In the summer of 1945, as the world edged closer to the precipice of peace, the same organization, now renamed the Signal Security Agency (SSA), occupied the entire campus of Arlington Hall, a former school for girls in the Virginia suburbs of the capital, from which headquarters it directed the activities of more than ten thousand managers, cryptanalysts, translators, intercept operators, and clerks. Eleven major intercept stations, some as close as the green Virginia countryside, others as distant as the dusty plains of the Horn of Africa, enveloped the globe in an electronic net that regularly monitored more than three hundred foreign radio transmitters and scooped from the ether as many as 380,000 radio messages a month. Wartime censorship authorities (with whom foreign embassies and consulates in the United States had to file copies of every communication they sent or received via commercial cable and radio facilities) contributed additional messages. At Arlington Hall, cryptanalysts (often collaborating closely with their British counterparts) cracked the diplomatic codes and ciphers of some sixty governments, while translators handled decrypts in twenty-five languages. The cracking of PURPLE, the machine cipher that carried the most secret communications of the Japanese foreign ministry, is well known. Less known, but no less important, is a string of successes against the high-grade diplomatic cryptosystems of other Axis powers (Germany and Italy), important neutrals (Spain, Switzerland, and Turkey), and even allies (Free France) that offered American policymakers a secret and privileged perspective on the diplomatic intentions and activities of countries around the world. Although the actual impact of these successes upon American diplomacy and military strategy was uneven, there can be no doubt that the organizational effort was impressive, the technical achievements awesome, and the production enormous.2