Alan Turing

The bombe helped the Allies win World War II. Nope, that’s not a typo. The bombe was a machine designed by Alan Turing to decipher encrypted German messages. With the bombe, the Allies knew exactly what the Germans’ plans were, allowing them to move troops out of danger and invade at opportune moments. Because of this — and other remarkable achievements — Alan Turing is considered to be a war hero who helped win the war.

The Bombe

In addition to the soldiers fighting at the front lines, Britain had another army at Bletchley Park where thousands of crossword enthusiasts, chess players, codebreakers, and mathematicians were all working toward one goal: decrypting Enigma messages. Originally a machine for commercial use, the Enigma was adopted and improved upon by the German military to send coded messages. The Enigma was definitely a complex machine; it was so complex that the Germans thought they had come up with a way to create unbreakable code.

The Enigma looked like a typewriter, except that above the keyboard was another set of 26 letters that would light up on each keypress. Pressing a key on the keyboard would result in a completely different letter lighting up. To convert a regular message into a coded message, the typist would press the key for a letter in the regular message and write down the letter that lit up. The result would be a random string of letters. For example, pressing ‘H’ might lead to ‘Q’ lighting up, and pressing ‘I’ might lead to ‘K’ lighting up. So the message “HI” would be encoded as “QK”. This method of encoding is called a substitution cipher.

Part of what made it complex — and seemingly unbreakable — was that ‘H’ wasn’t always replaced with ‘Q’. In fact, pressing the same key repeatedly resulted in different letters lighting up each time. This prevented codebreakers from analyzing letter frequency and matching patterns. The letter that would light up was determined by three components: a plugboard consisting of 10 plugs, a set of three rotating wheels called rotors, and a reflector. Each component mapped each letter to a different letter. In a sample scenario, pressing the ‘B’ key on the keyboard would send an electrical current to the plugboard, where ‘B’ might be mapped to ‘S’. Then the current would go through each of the three rotors, where ‘S’ might become ‘W’, ‘W’ might become ‘A’, and ‘A’ might become ‘U’. After that, the current would go through the reflector, where ‘U’ might become ‘T’, and then go back through the rotors and the plugboard again (and thus have the letter go through four more changes) to get the final letter that would light up. What made it possible for the same letter to map to a different letter each time was the fact that the rotors would spin on every keypress, changing the path of the electrical current, and therefore the letter that would light up.

The other part of Enigma that made it so complex was the fact that there was almost 159 quintillion ways (158,962,555,217,826,360,000 to be exact) the components of Enigma could be arranged to produce a coded message. However, to complicate matters further, the Germans would change the Enigma settings everyday, all of which were listed in a codebook that only the Germans had so they knew how to set their Enigma machines. Everyday, the codebreakers at Bletchley Park had 24 hours to figure out the one configuration that was used for that day. When the next day came, all their previous work would be useless.

The Enigma

Photo Credit - Annalisa Pogliana, Milano, Italy - Museo scienza e tecnologia Milano

It was an extremely difficult task, but the codebreakers did have some help. They knew about how Enigma worked because Polish codebreakers had been working on breaking Enigma since 1931. With secretly obtained documents containing the instructions and settings for the Enigma, the Polish codebreakers had managed to actually break the Enigma with their machine called the bomba — that is, until the Germans modified their machines in 1939. Before Poland was invaded, they transferred all of their work and knowledge to Bletchley Park, where Alan Turing improved upon their bomba to design his bombe.

Alan Turing was a mathematician and codebreaker. Regarded as a genius by those around him, he is considered to be the father of computer science and artificial intelligence. Before the war, he came up with the idea of a universal computing machine, later known as Turing machines, which is a theoretical model of a simple, abstract computer. Turing machines help us understand which problems are solvable by computers.

Enigma Key List

Alan Turing was fascinated with the idea of automating tasks. Fortunately for the codebreaking team, he had the genius to recognize that he could automate the codebreaking process. A well-known flaw in the Enigma machine was that a letter was never replaced by itself. Exploiting this, the codebreakers would take stock phrases, like “weather report” for example, and compare it to an encoded message to find a pattern where the coded letters did not match the letters of the stock phrase. Alan Turing realized that this part of the codebreaking process could be automated, making it much faster. With this in mind, he designed the bombe, a large device with a bunch of rotating drums that simulated the spinning rotors on the Enigma. Instead of finding the one correct setting, the bombe exploited the flaw in the Enigma machine to rule out all the impossible Enigma settings, leaving the codebreakers only a few settings they had to manually check. Once they found the correct setting, they knew exactly what the Germans were communicating to each other. Crucial information that was believed to be hidden was now wide open, eventually leading to an Allied victory.

Historians estimate that Alan Turing’s contributions may have helped shorten the war by two to four years and saved about 14 to 21 million lives. In fact, Winston Churchill was reported to have told King George VI that it was because of decryption that they won the war. World War II was more than a war of guns and bombs. It was a war of information. It was a war where the bombe and Enigma were pitted against each other to see which machine had ultimate control over communication. This constant battle over the transmission of information sparked the Age of Information; in fact, the first modern computers were constructed right after the war using technology developed during the war.

The Age of Information began with one computer scientist who built a computer that helped us win the war. Today, one computer scientist can build a piece of software that impacts millions of lives. Today, one computer scientist can revolutionize every field of human achievement — whether it be science, technology, engineering, math, art, or even basic human communication. And this is possible because of Alan Turing’s contributions to the development of modern computing. Alan Turing, the father of computer science, gave us computer science as we know it.

For further reading, check out our sources below:

• 158,962,555,217,826,360,000 (Enigma Machine) - https://www.youtube.com/watch?v=G2_Q9FoD-oQ

• Flaw in the Enigma Code - https://www.youtube.com/watch?v=V4V2bpZlqx8

• Turing’s Enigma Problem (Part 1) - https://www.youtube.com/watch?v=d2NWPG2gB_A

• Tackling Enigma (Turing’s Enigma Problem Part 2) - https://www.youtube.com/watch?v=kj_7Jc1mS9k

• How does the Enigma work? - http://russells.freeshell.org/enigma/how.html

• Alan Turing: The codebreaker who saved ‘millions of lives’ - https://www.bbc.com/news/technology–18419691

• Decoding Nazi Secrets - https://www.pbs.org/wgbh/nova/transcripts/2615decoding.html

• Enigma machine - https://en.wikipedia.org/wiki/Enigma_machine

• Alan Turing - https://en.wikipedia.org/wiki/Alan_Turing

• Bombe - https://en.wikipedia.org/wiki/Bombe