Book Review | The Enigma Story: The Truth Behind the ‘Unbreakable’ World War II Cipher
Reviewed by Charles Gundersen, museum volunteer
Comments of the author are his and do not represent the policy or position of the U.S. Navy.
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Can’t read this? Good, you are not supposed to unless you have an Enigma machine.
But, if you don’t have one, you could almost build your own Enigma machine from reading this book and operate it to encipher your messages to special people you don’t want others to know about. Then, turn around and decipher their replies. Finally, in the name of balance, this book explains the methods used to break into the encrypted message and read its secrets about the same time it was being read. The British did so well they could read German messages at approximately the same time as the enemy.
Knowledge of this capability would have been banned in this country during World War II. Because if the Germans found out we broke their code they would have surely changed their coding system, leaving us “blind.”
However, it was the British themselves that unleashed to the world an entity named Ultra in the 1970s. This broke the ice on divulging the coding secrets used by Germany during the war. From this time on, anyone could become a cryptanalyst and play with other people’s encrypted messages — except for the “elephant in the room” referred to as the Bombe. One used this very large machine, or a room full of them, to help break into the Enigma-generated communications.
This book is the story of a machine and is very well written. It would be of interest to anyone curious to know the workings of this secret-producing machine. Don’t worry, there aren’t any equations, just a bit of “crypto-speak.” The author does a good job in explaining the concepts of how the code was broken and how these two machines (Enigma and Bombe) interact. However, in a few places, there are some very large numbers.
During World War II, the Enigma machine was used most often on German U-boats to contact their bases in France and Norway. These radio frequency messages were intercepted by many of the radio antennas at Allied shore stations. Upon receipt of the enciphered messages, the stations relayed them to Bletchley Park in London or Dayton, Ohio, for deciphering into German. Then the message was translated into English. This work greatly helped in suppressing the threat of the U-Boats prowling the North Atlantic convoy routes. Not only was it used to vector Allied Anti-Submarine Warfare assets to the site of U-Boat wolf-packs, it was also used to route Allied convoys around the U-Boats.
The story, as told in this book, begins in the time of the Roman Empire and explains how messages were first encrypted. Basically, if you write a message and interchange every letter with another letter, you will have unreadable gibberish. But, if you use a chart that tells you which letter is to be interchanged with another letter, you have an encrypted message.
I’m glad the author (yes, he is related to Alan Turning the father of the British Bombe) described the big Bombe machine. Without divulging too much, I’ll just say it was used to locate possible settings the user needed in order to set up the Enigma machine before typing in an encrypted message to obtain the deciphered plain text. What proved to be interesting was the input into the Bombe consisted mainly of guesses — a few words that could be in the secret message (these guesses were called “cribs”). And the goal of the Bombe was to eliminate Enigma settings which would not work. When the Bombe cranked to a stop, its output was rushed to an Allied version of the Enigma to see if some readable German text was its output.
This all sounds easy enough until you remember there were an astronomically large number (a number almost as big as Avogadro’s number: 6.02 times 10 to the 23rd power) of settings that could be applied to the Enigma.
This book walks us through the process. The first thing the Enigma operator at Bletchley Park had to do was select three rotors out of the stack of five rotors (it should be noted the wiring within each rotor had to be painstakingly stolen from the Germans). Next the operator had to rotate a ring on each rotor and snap it into place. This was followed by the installation of the rotor into the Enigma, and rotating it to one of the settings discovered by the Bombe. And also, we cannot forget to wire up the Plugboard with a maximum of 10 wires according to another output from the Bombe run.
Just when you thought it couldn’t become any more complicated, the Germans introduced a 4th rotor — a rotatable turnaround rotor — including more tricks to keep the British and Americans guessing.
If you have the patience, it’s all here. The Enigma story, stem to stern.