Cryptography in World War I: The History of the Efforts to Make and Break Secret Codes during the Great War

World War I stood apart in many ways from earlier wars, not least in the way that it reached to nearly every corner of the planet and involved a noticeable segment of humanity's collective resources. Battles erupted not only on land and the sea's surface as they had for centuries, but also in the ocean depths and the windswept heights of the sky. Nearly every conceivable terrain saw use as a battlefield: the neat farmland and small towns of Western Europe; the streets of major cities; thick forests; open steppes stretching for hundreds of miles; deserts in Africa; rugged mountain ranges; and many other regions of the globe. But one of the war's most crucial struggles happened in the realm of the unseen, inside the human mind and amid the invisible flow of radio waves. Every war is a battle of wits as intelligence-gathering, tactics, and strategies clash, from the level of individual action up to the grand, overarching schemes of generals and statesmen. Intelligence took on a freshly urgent aspect in the Great War, however, as the fates of offensives, armies, and nations came to hang on the struggle to decrypt vital enemy radio traffic and military communications.

World War I was also the first major conflict in which new electronic means of transmitting and receiving messages became a major factor in political and military operations. The electric telegraph was developed in the first half of the 19th century, and by 1850, there were several telegraph companies around the world providing a service that allowed virtually instantaneous communication over long distances. This was a major breakthrough, but the telegraph depended on the availability of wires to transmit messages between stations, meaning that if these wires were broken or damaged, communications were cut off.

Late in the 19th century, there was another new development, the telephone, though this too relied on wires to transmit and receive information. At the same time, there was a new invention that provided instant voice and Morse code communication over long distances that did not require wires. Initially called wireless, radio was quickly adopted by armies around the world as a way of providing rapid communication between military units. By the time World War I began in 1914, all the major nations involved had provided their forces with some form of radio equipment.

Of course, this came with a fundamental problem: radio, telephone, and telegraph messages could be intercepted by the enemy, potentially giving them notice of impending operations. To protect these electronic messages from being read by the enemy, armies began to use codes and ciphers to disguise the meaning of messages. Teams were created to devise effective codes and ciphers, and these were quickly followed by other teams whose role was to attempt to break the codes and ciphers used by the other side. As a result, a secret war began, almost completely hidden from public view, as the belligerents devised complex ways of hiding the real meaning of their own messages while simultaneously attempting to understand those of the enemy.