Or you’re just having a human day, with possibly too much blood in your caffeine stream. 
I suspect as much too.
The internet claims it was not a myth, even if it was not universall in all messages, it did appear often enough to be of help. That, and weather reports, that are quite standardised, and places that could be expected to be mentioned in some messages.
Be it as it may, it was hard work, but the Nazis were overconfident. The German they used was plain German, with no additional encrypting, and too often formulaic. Or, as the OP asked: coherent German.
I’m not saying it’s impossible, I’m just saying the internet likes an entertaining story. A brief scan just now didn’t find any primary sources.
I think I’ve heard of some known stations using things like their girlfriend’s name, too, though I don’t remember the context where it would be used. End-of-message padding to make all messages the same length, maybe?
The crib “Heil Hitler” was artistic license in a scene from The Imitation Game. Has a more dramatic effect than “weather report” (“wettervorhersage”). The key point of the scenewas the realization that there would be commonly repeated phrases that could be used as cribs.
Coincidentally, I just watched a documentary on this. One of the big breaks that allied codebreakers got was when EVERY German commander in the field (above a certain level) sent congratulations to Hitler on his birthday. That many messages with a common theme greatly eased the problem of breaking that days’ code key.
I’m surprised the Japanese even knew it was Navajo to begin with.
No, this part is some type of urban myth. I’m not even sure where it comes from.
It was literally the first three as part of the procedure to verify each day’s machine settings. At least until May of 1940. There’s a pretty good description of the Enigma workings at PBS. The weakness of this scheme is apparent - you know the 1st/4th, 2nd/5th, and 3rd/6th characters entered are the same but get encrypted differently.
- He turned his three wheels to a position chosen at random, the “indicator-setting” (e.g., JCM).
- He twice keyed his own randomly selected choice of text-setting, or “message-setting” (e.g., BGZBGZ).
- This came out as the “indicator” (e.g., TNUFDQ).
- He set his wheels at BGZ and keyed the clear text of the message, thus obtaining the enciphered text, letter by letter.
The Enigma design was originally for business (financial) communications. And in those, you want to be very accurate and reduce the risk of possible transmission errors – so the cost of increased length is acceptable. If you send “buy at five hundred twenty six”, loss or garbelled transmission of one or two characters is less likely to invalidate the message than ‘buy at 526”.
Even today, use of written-out numbers is used in financial documents. Like when you write the amount of a check both in numeric digits and written words, or in legal contracts, which commonly say things like “Rent shall $1200 (one thousand two hundred dollars) per month”.
Ah, I forgot that the predecessor of the Enigma was a civil business machine. Should have made it even more vulnerable to decoders, who must have had access to those machines that had been on the free market before the war, maybe even with documentation.
The Navajo code had a couple hundred ‘code words’ for military things (like the Navajo word for whale = battleship, Navajo for iron fish = submarine) – those made up most of the message. This spelled-out code was actually used only for special cases where they had no defined code word.
And they made it a bit more difficult: several Navajo words like those for apple, ant, axe, all equated to “A”; dog, devil, or deer equated to “D”, etc. And the talkers were encouraged to alternate between them.
That was what happened with the Coventry raid in November 1940. Bletchley Park had identified that the Germans were planning a raid, called Unternehmen Mondscheinsonate (Operation Moonlight Sonata), and that there were three possible targets:
The targets had the code names Einheitpreis, Regenschirm and Korn. The day before the Coventry raid, a prisoner mentioned Regenschirm (umbrella ), which was assumed to mean umbrella man (Neville Chamberlain) who was born in Birmingham, it would be bombed on 19/20 November. Einheitpreis (unit-price ) was identified later, which was tied to sixpence at Woolworths, meaning Wolverhampton. Korn was unidentified.
Korn was Coventry.
The Navajo code had a kind of secondary code because the U.S. military language used a lot of terms that the Navajos had no word for, so they came up with arbitrary Navajo words to represent them. That’s probably why it sounded like nonsense to him.
My understanding is that the enigma machines were designed with a series of wheels inside them which had electronic circuit lines running through them. So if you typed in the letter F, the signal from the F-key would run through the circuit lines and then a different letter, let’s say L, would light up. But in addition to sending this signal, every keypunch would cause the wheels to rotate to a new position. So if you typed in a second F, this time the W might light up.
So you couldn’t use normal letter or word frequencies to decipher a message because even if the same word appeared multiple times in a message, it would be ciphered differently each time.
Another advantage of the enigma machine was that it was pretty easy to decipher a message if you knew the settings. You just put the wheels into the machine at the same position they started in and typed in the ciphered message. The electronic circuits in the wheels would now run in reverse and light up the original letters. Of course, this only worked if you knew the original wheel setting. So the security of using an enigma machine was built around making sure the enemy didn’t get the scheduled list of settings. If you didn’t know the setting, there were literally millions of possibilities.
One problem with the enigma machines is that they never would double back and substitute a letter for itself. So you knew that the letters in the ciphered message would never appear in the same position in the original message.
Another weakness were Germans, like the one described above, who fell into patterns like starting all messages with HEILHITLER. If you knew the original message started with the letters HEILHITLER and you had the ciphered message that started with the letters JRVOFGGEPO it would, in theory, be possible to figure out what combination of settings would turn JRVOFGGEPO into HEILHITLER. Then once you knew the settings, you could use them to decipher the rest of the message. And any other messages that were working from the same settings list.
The problem was finding the settings in the real world. You would have to test millions of possibilities to find which one produced the expected result. Humans couldn’t work fast enough to test all of the possibilities. But computers, even early ones, could check the possibilities much faster.
The thing that struck me when I visited Bletchley was that, even when the complexities of the machines were overcome, and even when the German has been translated into militarily comprehensive text, it still needed to be put into context and connections made with other relevant data. The sheer size of effort, the numbers of people and volumes of paper/card indexes to put together useful information - and at speed - and managing relationships with the ultimate military recipients: it’s mind-boggling.
And that they kept the entire operation a complete secret and kept that secret for decades. There are stories of spouses who worked on different aspects of the operation, met after the war and didn’t know each other were there until decades later when it was declassified.
During the war the Abwehr became aware that the Soviets had a High-level intelligence source which was codenamed WERTHER. They concluded that WERTHER must be an officer on the OKW, such was the quality and breadth of the information he was supplying, a staff officer at lower level would have had access to such a wide range. A long and diligent search failed any candidate .
In retrospect WERTHER was probably a means of disguising the ULTRA information the Western Allies were supplying to the Soviets.
Why? There were enough Japanese in the USA, and they were not treated so well that they were sure to remain loyal to you and not to the Tennō.
That bit of information could be easy to find. Using it, on the other hand, was a different thing.
Not that the Navajo were treated all too well either. And still, none defected to the enemy, it seems. Lucky you.
Firstly why would that be easy? I would have thought the use of Navajo would be a pretty well kept secret.
Secondly your can’t assume you know where Dopers are from.