Ultra and Enigma

In the early 1920s a German manufacturer advertised an enciphering machine that it declared unbreakable. The machine, called the Enigma, used a series of rotors and electrical plugs to encipher a message before transmission. The operator would type what was to be transmitted into the machine after moving its rotors to certain settings, and the machine would then encipher the message before transmission. The receiving station, which would know the settings for that particular time or day, would feed the enciphered transmission into the machine in reverse order to obtain the original plain text message.

Confronted with the task of defending Germany's frontiers with an army limited to 100,000 by the Treaty of Versailles against the vastly superior forces of France and her Eastern European allies, Poland and Czechoslovakia, the German Army immediately bought the machine and began adapting it to military purposes. Given the increasing sophistication of radio as well as the need to control military forces over large distances, the Enigma machine offered potential for protecting message traffic between combat units and their controlling headquarters.

Unbeknownst to the Germans, the Poles had discovered that their neighbors were using a complex enciphering machine. Both by espionage and “borrowing” from the Warsaw post office over a weekend an Enigma machine that was being sent to the German Embassy in Warsaw under diplomatic immunity, the Poles soon had a working copy of Enigma. To decipher German transmissions, the Poles put their best theoretical mathematicians to work. For much of the 1930s they succeeded in reading the vast majority of the German Army's radio traffic. But with the approach of war, the Germans added a number of refinements to Enigma, and in early 1939 the Poles were no longer able to break into German message traffic. In one of the most important meetings of 1939, the Poles turned over the results of their work and several copies of Enigma to the British and French in late August.

Hitherto the British had underfunded their codebreaking organization, the Government Code and Cypher School (GCCS), located at Bletchley Park. Thus, GCCS had had no success in unscrambling the vast numbers of German encoded radio transmissions, which the three German services and other government organizations were using. The Polish contribution was, therefore, monumental because it significantly advanced what British cryptologists knew about the method the Germans were using to protect their radio transmissions. Nevertheless, throughout the rest of 1939 and the first half of 1940, the British had little success in breaking into the German message traffic. In fact, the Enigma system should have remained largely unbreakable throughout the war. But the Germans transmitted so many messages from so many different stations and possessed such a belief in the superiority of their technology that a number of users compromised the codes by sloppy procedures, such as consistent message formats, transmitting messages at the same time every day, and by transmitting huge numbers of unimportant messages.

By spring 1940, Bletchley Park began to have some minor success. But the intelligence gained was spotty at best. The initial decrypts did little to save the Allies from defeat in Scandinavia and northwest Europe in spring 1940. However, they did provide some help during the battle of Britain. In one important case they provided R. V. Jones, the young head of British scientific intelligence, with a crucial clue that allowed him to determine the frequency on [Page 854]which a German blind bombing device was operating, thus setting the initial conditions for the defensive measures that mitigated the impact of the German Blitz—the nighttime bombing offensive against Britain staged throughout the winter of 1940–41.

...