Only holders of a cipher "key" could divine the underlying text, but possessing the codebooks made the whole process of solving the messages far simpler. To exploit these treasures the Admiralty established Room 40.
In "Dead Wake: The Last Crossing of the Lusitania," Erik Larson describes how secure communications during World War I relied heavily on cipher keys that only certain individuals could decode. The complexity of deciphering these messages was significantly reduced by the possession of codebooks, which served as valuable resources for those involved in intelligence work.
To take advantage of these codebooks and enhance their capabilities in breaking messages, the British Admiralty...
