One of the greatest advantages that the United States and Great Britain had in their struggle against Nazi Germany and Imperial Japan during the Second World War was their ability to decode or decipher the secret military and diplomatic messages of the Axis powers. Although this ability was limited in many ways, it provided important intelligence about Axis military operations, Axis appreciation of the Allied strategy, and international relations during the war.

The Allied exploitation of Germany's Enigma cipher machine, referred to popularly as “Ultra,” was finally revealed with the publication of F. W. Winterbotham's The Ultra Secret in 1974. This book provided information about an aspect of the war that had only been hinted at over the thirty years since the war ended, though there had been a partial revelation years before about America's prewar exploitation of Japan's diplomatic cipher machine, code named “Purple.” Many memoirs and histories followed that revealed more of the Allied code-breaking success.

Not long after these revelations, scholars began to ask what Allied code-breaking efforts revealed about the Nazi plans to eliminate Jews and others considered inferior by the Third Reich. In the early 1980s, the first histories were published that contained information about the Holocaust obtained from code-breaking. These few histories were quite limited and cited no archival records, which remained classified and unavailable to the public. It was not until 1996 that the National Security Agency (NSA) released to the U.S.