The Bombe - reality or cover-up

: history, September 26 2025 ▶

Disclaimer: explaining the very details of mathematics involved is far beyond my capabilities. I'm still a human with a life. If you want to test/challenge the methods to their "nuts and bolts", please do it on your own accord. The goal of this article is to be understandable.

As a person, genuinely interested in the area of cryptography, I do some reading on the recent advances, gaps, hacks, etc. In our modern times, some cases become known, but most of them are either completely buried or inaccessible to the average person - sometimes due to the sheer complexity of the topic.
I've seen Enigma-s - that is the cryptographic machine, used by Germany during WW2. Developed in 1920s, it had several iterations, which I will try to position chronologically, focusing on the military models. And the allies broke it somehow. There are many movies, documentaries, articles about it, but I always felt something is missing. Something did not quite add-up, did not explain how this is possible. You see, when it comes to cracking a cypher, there are 2 scenarios. "Brute force" means you test every key against the encrypted text - plausible, but extremely time and resource consuming. "Exploiting cypher vulnerabilities" is the smarter, faster, but not guaranteed to produce any result. And throwing resources on something that vague, does not sound to me like something a military intelligence would do.
In my younger days I thought Alan Turing created an amazing computer, which could decipher messages directly. Later I got some knowledge on how the Enigma works, and thought "wait a minute, it will still take 1.6 quadrillion years, so how did they do it?". Then I had this idea it was a cover-up for some high-ranked spy, who provided all the keys in advance. I partially changed my mind only recently. Ultimately, the truth may never be known and is most likely in the grey zone.
Mr. Turing was not alone to tackle such impossible task. It stared with the Polish "bomba kryptologiczna".

"A bombe run" involved a cryptanalyst first obtaining a crib — a section of plaintext supposedly corresponding to the ciphertext. Germans tend to send same messages on a schedule, so once you know that in Cologne the weather is fine and the message is the regular daily report, you may try to find out with which sequence of rotors it was encrypted. If you are successful, then you can test the same key against other communication.
The Polish got their hands on one of the early Enigmas (M3 with 3 rotors) on 1927-28 and in December 1932, Marian Rejewski managed to break the code of the Army one - with plugboard (Steckerbrett) additional to the rotors - a much more complex version. Germans, sensing something is fishy, ordered a settings change - monthly in February 1936, then daily in October of that year. Nevertheless, by January 1938, polish were decrypting 75% of the messages.
With the war looming on the horizon, the Polish government decided (July 1939) to share their achievement with their colleagues in Britain and France.

In Bletchley Park, On 17 January 1940, the Poles made the first break into wartime Enigma traffic – that from 28 October 1939. The first bombe was named "Victory". It was installed in "Hut 1" at Bletchley Park on 18 March 1940.
By the end of 1941 Germans suspected that Enigma is broken. Admiral Doniz ordered a new, 4 rotor version to be used. You can imagine the level of complexity an additional rotor introduces. But the caveat here was that the 4rth rotor did not move during message creation. 1450 M4 Enigmas were delivered in 1942 with 10^20 settings. In February 1942 Allies were no longer read the messages.
Next story is simply a movie script on its own (briefly mentioned in "Enigma" from 2001 though). In October 1942 a damaged German submarine, U559, was captured with functioning 4-rotor Enigma. Her crew left the boat without scuttling it and 3 sailors from HMS Petard swam to it and retrieved the critical device. 2 of them went down with the sinking submarine (later all received George Cross medals - one of the highest awards possible). Using this, Bletchley Park succeeded in breaking the first M4 naval Enigma messages on 13 December 1942. With a good crib and a well-chosen menu it wasn't unusual for a decrypt to be completed within an hour or two, in very lucky cases - in minutes. As before, the Turing's machine did not provide a clear solution, but narrowed down to a humanly-manageable task the possible keys to check. I think the British intelligence also helped a lot by "finding" code books (leaflets with the daily setting) more often than mentioned.
Back to my (naive) cover-up theory. I checked, year by year, how many decipher machines were built - 12 in the beginning, reaching more than 300 in 1945. This is a massive endeavor, both in UK and US, demanding thousands of workers (from 2-4 private companies). I cannot imagine somebody put so much effort and resources, just to hide some secret agents. On the other hand, how did such thing remained secret for more than 20 years, if so many people were involved? How did they build hundreds of devices per year, that should work perfectly every time, if it took 13 years to build a replica machine (finished in 2007, all other Bombe and documentation was destroyed just after the war)? What organizational precision is needed to operate dozens of such machines effectively? Isn't it possible someone created this "conducted, but meaningless chaos" in order to hide his operatives?
Some (biased) historians say that breaking the Enigma was the turning point of WW2.
It was not.
It was the battle of Kursk (5 July 1943 – 23 August 1943), involving ~10000 tanks, including the the largest single-day tank engagement: ~1,200 Soviet vs. ~500 German tanks at Prokhorovka on 12 July.
Nevertheless I do believe that Bletchley Park operations reduced the length of the war significantly and is one of the key events to pay attention to.
No such publicity received another set of machines - the most important which was the Colossus (equivalent clock of 5.8 MHz). Ten were in use by the war's end, the first becoming operational in December 1943. Designed to break The Lorenz SZ40, SZ42a and SZ42b rotor stream cipher machines. 2 Colossi survived till 1960, but then dismantled. It is the world's first programmable computer. The British did not know that Lorenz encryptors exist, they have never obtained or seen one, but managed to theorize, build and break them by just comparing 2 messages, that a German officer sent by mistake. ...or was it another great spy story? Details about both Bombe and Colossus were declassified in the 1970s.