Photo courtesy of Flickr: Ken Douglas
After signing the Treaty of Versailles in 1919, Germany's defense establishment was anxious to improve its compromised communications efforts and recognized the potential of a signaling machine that had been made for use in the business market.
The Enigma machine, developed by Dr. Arthur Scherbius, could transcribe coded information and was created with an eye to commercial businesses dealing in secure communications. In 1923 he established his Cipher Machines Corporation (Chiffriermaschinen Aktiengesellschaft) to manufacture his Enigma. Within three years the German navy began producing its own version with the army following suit in 1928 and the air force in 1933.
To operate Enigma, the user typed in a message and then scrambled it with three to five rotors that displayed different letters of the alphabet. The person who received the message had to know the exact settings of these notches so as to reconstitute the coded message. Over time, the basic machine became more advanced as German code experts added electronic circuits and plugs.
In 1931, German spy Hans Thilo Schmidt allowed French spies to take pictures of stolen Enigma manuals, however neither French nor British cryptoanalysts were able to break the cipher. After giving details of the code over to the Polish Cipher Bureau, progress was finally made. The Poles were able to reconstruct an Enigma machine to read the Wehrmacht's messages from 1933 and 1938.
Decoding Ultra Intelligence
With German invasion on the horizon in 1939, the Poles shared their secrets with the British. Britain's Government Code and Cipher School (GC&CS) at Bletchley Park became the epicenter for the Allies efforts to keep up with Germany's Enigma-coded war messages.
A troop of top mathematicians and problem-solvers were recruited and a bank of computers were brought in to work out the different possible permutations Enigma was capable of producing. The Germans were positive that their Enigma-coded messages could not be broken, so they communicated in that fashion for a number of purposes including: battlefield, at sea, aerial and for secret service communications. The British called any intelligence gathered from Enigma as "ultra" and it was considered top secret. As such, only a handful of select commanders were fully aware of the significance of Ultra, and most intelligence was used sparingly so as not to alert the Germans that their ciphers had been broken.
Despite the gathering of Ultra, this information had little bearing on Allied war efforts until 1941. In the spring a message was decrypted that detailed a military build-up before the invasion of Greece, however the Allies limited military force in the area prevented them from acting on the discovery.
Breaking the German Navy's Codes
At the time the greatest threat to the Allies came from attacks on their convoys in the North Atlantic. Bletchley's code-cracking efforts were redirected on breaking the codes of German U-boats. If the Allies knew where the German U-boats were hunting, they could redirect their ships away from these dangerous waters.
Because of the danger German U-boats posed to Allied forces, to keep up with the ever-changing Enigma codes it was decided the best method was to capture Enigma machines and code books from German vessels. A breakthrough occurred in March of 1941 when Krebs, a German trawler, was captured off of the coast of Norway, containing two Enigma machines and the Enigma code settings for the previous month. Bletchley codebreakers were able to crack the German naval code the following month. At the suggestion of Bletchley codebreaker Harry Hinsley, German weather and supply ships, in addition to war ships were sought after for Enigma machines and code books.
In February 1942, Germany responded to Bletchley's efforts by adding a fourth wheel to their navy's Enigma machines. The resulting code was named "Triton" by the Germans and "Shark" by the British. It wasn't until December 1942 that Shark was broken but Allies had to wait until August of the following year to read Naval Enigma.
Ending the War
While Ultra was no longer as important by D-Day in 1944, the Allies still did not want Germany to know that they were reading Enigma. Harry Hinsley suggested that Ultra intelligence obtained from decrypting Enigma cyphers significantly shortened the length of the war. Being privy to the enemy's operations proved invaluable. Without Ultra knowledge, Overlord (as D-Day landing plans were called) may have been deferred until 1946.
By that time, however, Germany may have hit the Allies with V-weapons, or worse. While Enigma victories always required supplemental intelligence, the Allies clearly thought it was an asset, as they kept the secret of Enigma until 1974.
For further information on Enigma and code-cracking, explore the following resources: