What was it that made the British Bombe computer better than the Polish Bomba computer?

Amazingly enough, the most effective enhancements made to the British Bombe as it was converted from the Polish Bomba were made by taking advantage of German human errors, bad habits, and carelessness!

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The French and British cryptanalysts started working on cracking the German Enigma in 1932. They worked on this for six years and made very little progress. They started believing that the Enigma is just simply impossible to crack.

Their biggest breakthrough came on July 24 and 25 of 1939, when they met with Marian Rejewski in Poland, and he gave them the complete specifications for a machine that he built called the Bomba. With the Bomba, Rejewski was able to decript about 70% of the German messages.

World War II started on September 1, 1939, when Germany invaded Poland. Britain and France declared war on Germany on September 3, 1939.

It became very urgent to have a good ability to decript German Enigma messages, and to have it very quickly. This time, Britain decided to recruit their best mathematicians, chess players, bridge players, and solvers of crossword puzzles to work on cracking the Enigma.

Among the mathematicians that were hired were two outstanding ones: Gordon Welchman and Alan Turing. Of the two, Welchman was older and was the dean of a college at Cambridge University, while Turing just returned from Princeton University with a brand new Ph.D. However, since Turing amazed the whole world with the invention of his Turing Machine in a paper that he wrote just two years earlier, he was probably respected as the more talented mathematician.

Welchman was assigned to be the leader of the team in Hut 6 where the deciphering of the German Army and Air Force messages were done; these came from Enigma machines with only 3 rotors. Turing was given the more challenging task of leading the team in Hut 8, to decript the messages from the German Navy Enigma, having 4 or 5 rotors.

It was Turing who very strongly advocated using the Polish Bomba machine. Starting with the specifications from Marian Rejewski, he added some improvements of his own, and since it now was no longer identical to what Rejewski had, he also decided to slightly change the name from Bomba to Bombe.

Gordon Welchman's approach was different. He was yet unable to decript the messages, but he did know where each message originated and who the intended recipient was. By collecting and compiling this information, he started something called Traffic Analysis, which proved to be extremely valuable in determining the locations and estimated strengths of German Army and Air Force units.

Meanwhile, Welchman also assisted Turing in designing and building the Bombe. The Diagonal Board, placed on the back of the Bombe, was Welchman's idea. It made the Bombe much more efficient, and Turing himself thought this was a brilliant enhancement.

It took nine months for Turing and his team to build the first Bombe, and then it was placed in Hut 6 for use by Gordon Welchman and his team because cracking the German Army and Air Force Enigmas was a much higher priority than the Naval Enigmas. However, work was now underway to make more copies of the Bombe (and even some with more improvements) so that Alan Turing soon had his own Bombe for use in Hut 8.

NOW, HERE COMES THE GOOD PART !!!

Well, before we get to the good part, we first need to explain something about how the Enigma was used.

At the beginning of each month, every Enigma operator was given a secret Key Sheet. The Key Sheet would instruct the operator on how to reset the Enigma machine at midnight, and it would then have that setting for the rest of the day. It explained how to rewire the plugboard, which rotors should be selected, and in which order should the selected rotors be placed into the Enigma machine. It also gave a different code for each day. (It was a 3-letter code for 3-rotor Enigma machines, a 4-letter code for 4-rotor Enigma machines, etc.) The operators then aligned the rotors with that code before each message was encripted.

When the operators underwent their training, they were told to come up with a code of their own. (It was supposed to be 3-letter code for a machine with 3 rotors, a 4-letter code for a machine with 4 rotors, etc.) During the training, it was stressed that the letters they pick must be randomly chosen. Then, at the start of the message, they should set the machine to the letters on the Key Sheet, enter the random letters they selected twice, then reset the rotors to the letters they just encripted, and finally encript the rest of the message.

Furthermore, the operators were trained to select a different code of their own for every single message they send. When you think about it, this idea is simply genius! This is almost just like having a different Key Sheet for every single message! Who could possibly crack the Enigma now??!!

OK! OK! THE GOOD PART COMES NOW!!

What actually happened was that, when some of the German Enigma operators selected random letters, they would usually select something like AAA, or ABC, or QWE (because they happen to be adjacent keys on the keyboard). When Alan Turing noticed that this was happening, he instructed the Bombe Programmers to set up the Bombes to check for these "randomly-selected" letters first. This really cut down on the time necessary to break the Enigma messages every day.

There were thousands of people working at Bletchley Park. Many of them worked as Bombe Programmers, and they were all women. They programmed the Bombes by rewiring plugboards, flipping switches, and turning dials to different positions, all based on written instructions given to them by Alan Turing.

There were also those whose only job was to listen to all German radio messages sent in Morse Code and record them on paper. They worked at Bletchley Park, and also in many listening posts around the country. In time, just by listening to the clicking of the Morse Code messages, they were able to tell which messages were transmitted by the same German operator. This information also turned out to be very valuable.

NOW, THE STORY GETS EVEN BETTER!!

One day, Alan Turing found out from one of the workers at Bletchley Park, that there was a German sailor who always, without fail, would pick the random letters to be his girlfriend's name. (He was most definitely trained to select different random letters before every message encrypted with the Enigma, but maybe he thought that this was just some silly unnecessary requirement?) This moment is wonderfully dramatized in the following movie clip. (If we can believe the movie clip, then we know he was a sailor, because his girlfriend's name had five letters, and it was the German Navy that had Enigmas with five rotors.) This was probably Alan Turing's geatest breakthrough in deciphering the German Naval Enigma messages. Not only was he now able to easily decode all messages sent by this sailor, but it also gave the Bombes a head start on determining the settings in the Key Sheets for all Enigma machines for that day.

In time, other German Enigma operators were found making the same blunder. For example, there was one German soldier who always set his random setting to TOM before sending every message. (It was found out later that he did this because his hero was the American western cowboy star Tom Mix.)

Another good breakthrough for Turing came when he noticed that certain German words would always appear in the same place in the secret messages. The first message every day sent out by German U-Boats started with a weather report. Thus, it was a good idea to look for the German words meaning weather, rain, wind, etc., at the beginning of each of those messages. Also, some Enigma operators would begin their messages with Heil Hitler while some other operators would end with Heil Hitler. (This discovery was also nicely dramatized in the following movie clip.) Knowing which operator was sending the message, this would be another clue that could be programmed into the Bombes.

As time went on, the Germans started catching on, that perhaps having the Enigma operators select their own random settings before each message was not a good idea. When that happened, Admiral Doenitz issued an order, that all operators of German Navy Enigmas skip the step of selecting their own random settings for the Enigma machines, and just use the settings that were in the Key Sheets. (So, perhaps this brilliant idea that the Germans had of making the Enigmas completely uncrackable was not so genius after all!!)

Of course, by this time, there were hundreds of Bombes (and also other computers similar to Bombes--like the Colossus) running non-stop, on both sides of the Atlantic. The Bombe Programmers in Washington, D.C. were all women--more specifically, they were all WAACs and Waves.