Nobody But Us

The Rise and Fall of the Golden Age of Signals Intelligence

Abstract

The United States’ National Cryptologic Museum in Fort Meade, Maryland, displays versions of two important encryption machines. The first is the Enigma machine, the most famous cryptographic apparatus ever built. The second machine, less well known, is called SIGABA. These devices are similar in certain important respects. Each employs an electromechanical rotor-based design. Each was used during World War II; the Nazis deployed Enigma while US forces relied on SIGABA. It is no exaggeration to say that, during the conflict, these machines protected—or tried to protect—some of the most important messages in the world.

Both sides treated the machines as closely guarded secrets. The United States took enormous steps to protect SIGABA, requiring that it only be deployed to areas where American forces could guard it and instructing these forces to destroy the machines before they could be captured. American cryptologists feared what could happen if the enemy gained access to SIGABA and reverse engineered it. On the other hand, the Allies achieved an enormous success when they captured an Enigma machine. Acquiring the physical device was one of the many factors that enabled the Allies to eventually understand its workings and decrypt the messages it protected.