From Finishing School to Codebreaking Factory
In 1927, Arlington Hall opened as a junior college for young women, its colonial-style main building looking over a 100-acre campus of landscaped gardens and lawns. This quiet academic setting was completely transformed by World War II. In April 1942, officers from the U.S. Army's Signal Intelligence Service (SIS), the nation's codebreaking division, happened upon the school while searching for a new headquarters. They had outgrown their cramped offices in Washington D.C. and needed a location that was both accessible and secure.
On June 10, 1942, the U.S. Army acquired the college under the War Powers Act. A double chain-link fence was erected, and the school for "genteel young ladies" became a top-secret intelligence facility known as Arlington Hall Station. The campus rapidly expanded with the construction of barracks, new operations buildings, and support facilities to accommodate a massive influx of personnel. By the end of the war, the workforce had swelled to nearly 8,000 military and civilian staff, the majority of whom were women recruited from colleges and teaching professions for their aptitude in mathematics and languages.
Cracking the PURPLE Cipher
The most important scientific achievement associated with Arlington Hall is the breaking of Japan's highest-level diplomatic cipher, codenamed PURPLE. The cipher was generated by a machine that used telephone-style stepping switches to encrypt messages, a system far more complex than the rotor-based Enigma used by the Germans. The task of breaking it fell to a team of cryptanalysts led by the brilliant William F. Friedman.
The breakthrough occurred on September 20, 1940, over a year before the attack on Pearl Harbor. After 18 months of intensive analysis, a team led by Friedman and Frank Rowlett reverse-engineered the logic of the PURPLE machine without ever having seen one. Mathematician Genevieve Grotjan made the initial discovery by identifying cyclical patterns in the encrypted text, which allowed the team to deduce the machine's wiring. The SIS then constructed its own analog machine, which allowed them to read Japan's diplomatic communications almost as fast as the intended recipients. This stream of intelligence, codenamed "Magic," gave the Allies invaluable insight into Axis strategy and intentions throughout the war.