The Zimmermann Telegram

World War I began in 1914 as a fight among several European nations, while the United States pursued a policy of non-intervention. In fact, Woodrow Wilson was reelected President largely because “He kept us out of war”. But as the war unfolded in Europe, an intercepted telegram sent by the German Foreign Secretary, Arthur Zimmermann, to the Mexican government inflamed the U.S. public opinion and was one of the main reasons for the entry of the U.S. into WWI. This is the story of the encrypted telegram that changed the last century.


Area Mexico ceded to the United States in 1848, by [Kballen] via Wikimedia Commons
Germany was actively seeking to promote a war between Mexico and the U.S., in the hope to create a military distraction and avoid the entry of the U.S. into the war. After several unsuccessful attempts to spark a conflict, the Germans decided to offer Venustiano Carranza, the new Mexican president, the recovery of the lost territories of Texas, New Mexico and Arizona in case of a German victory. (California was not included, maybe because the Germans thought it would be an irresistible offer for the Japanese, in case they also wanted to declare war on the U.S.)

But how could the Germans convey this offer to the Mexicans? Three options were considered.  The first was to communicate the proposal to the Mexican ambassador in Berlin. The second, send the message via the Deutschland submarine that would land somewhere in the U.S. and then deliver it to the German embassy, to be forwarded on to the Mexicans. The third option was to send the proposal in a coded telegram using the best cryptographic techniques available.

The Mexican ambassador in Berlin was not trusted by Germany, so this option was considered too insecure. The second option offered the most secure method, but it was also the slowest. Therefore, the Germans went for the third option and on January 19, 1917, the German ambassador to Mexico, Heinrich von Eckardt, received the coded telegram from Zimmermann. The decoded text is as follows:

We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor in spite of this to keep the United States of America neutral. In the event of this not succeeding, we make Mexico a proposal of alliance on the following basis: make war together, make peace together, generous financial support and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona. The settlement in detail is left to you. You will inform the President of the above most secretly as soon as the outbreak of war with the United States of America is certain and add the suggestion that he should, on his own initiative, invite Japan to immediate adherence and at the same time mediate between Japan and ourselves. Please call the President’s attention to the fact that the ruthless employment of our submarines now offers the prospect of compelling England in a few months to make peace. Signed, ZIMMERMANN


A military commission was created by Mexican president Venustiano Carranza to study the German proposal. The commission recommended to refuse it, based on several reasons. First there was little chance that Mexico could win a war with the U.S. Second, a war against the U.S. would endanger Mexican relations with other nations. And third, there were serious doubts that Germany will keep the promise of “generous financial support”.

British intelligence intercepted and decoded the telegram, and released it to the U.S. on Feburary 24. That same day, President Wilson read the message, and went public with it on March 1st. The reaction of the American public proved to be just what was needed to change the non-intervention policy. The threat of a possible combination of Mexico, Japan, and Germany represented a nightmare. On March 20, President Wilson met with his cabinet, and found it in favor of entering the war. The American congress approved the declaration of war on Germany and its allies on April 6, with just one vote against.


ztel2Decoding the Zimmermann telegram is perhaps the most significant intelligence triumph for Britain during World War I. The telegram was intercepted and analyzed in the ultra-secret Room 40, a section of the British Admiralty for cryptanalysis efforts during WWI.

The Zimmerman telegram was coded using cypher 0075, a two-part code of 10,000 words and phrases numbered 0000 to 9999. In order to avoid frequency analysis, the numbers were randomly chosen, and additionally, each letter was individually coded using simple substitution. Of course, the cypher is secure as long as the code book remains secret. An older code, named 13040, was already been cracked by the British, but the newer code 0075 was considered secure. Code 13040 had about  25,000 plaintext elements and 75,000 code numbers. For instance, here are some examples from the codebook:
Februar 13605
fest 13732
finanzielle 13850
folgender 13918
Frieden 17142
Friedenschluss 17149
führung 17166
Ganz geheim 17214
Gebeit 17388
geheim 4377
Gemeinsame 4458

However, the Germans underestimated the British codebreakers. The telegram was first sent from Berlin to Washington on January 16 (using the U.S. diplomatic lines), intercepted by the British, and was partially decrypted by the people in Room 40. Even with an incomplete message, the intentions of Germany were evident. The British wanted to pass this information to the U.S., but to do so would reveal the eavesdropping on U.S. cables. At the same time, the Germans would realize that their new 0075 code had been broken.

In order to prove the telegram’s authenticity to the U.S. without German suspicion of code breaking, and without disclosing the fact that the British intelligence were spying on the U.S. cables, the British would tell the U.S. that the telegram was obtained by bribing a telegraph company employee in Mexico (the telegram was sent from the Germany embassy in Washington to Mexico). Moreover, the telegram sent to Mexico was coded using the older 13040 cipher, so, at worst, the Germans would think that the 13040 code was cracked.

In the end, Germany sealed its own fate, providing Britain with a way to push the U.S. into the war. President Wilson had said that it would be a “crime against civilisation” to lead his nation to war, but a single breakthrough by the codebreakers in Room 40 forced him to change his mind. It was a great triumph of cryptography that drew the United States into the war, and changed the course of history.

71 thoughts on “The Zimmermann Telegram

          1. A fair point. The Nazi Party’s precursor, the Pan-German nationalist and anti-Semitic German Workers’ Party, was founded on 5 January 1919. By the early 1920s, Adolf Hitler assumed control of the organization and renamed it the National Socialist German Workers’ Party (Nationalsozialistische Deutsche Arbeiterpartei, NSDAP) to broaden its appeal.

      1. They cracked it the old fashioned way. They could do that because it was an old fashioned cryptosystem. Enigma and the other advances made later changed all that, and required the British to leapfrog the state of the art in cryptanalysis, which they did thanks to the folks at Bletchley Park, including Alan Turing. But that’s a whole ‘mother story (and motion picture).

        1. One correction – Bletchley park cracked Enigma because Poland GAVE them all of their research on it, including a working machine itself when it was evident that they would not be able to defend against the German invasion…they even went to great lengths, including several people resisting german interrogation and torture to keep it all secret, so the Germans never even suspected that there was such large effort to break the code.
          Without that, the Brits would have had nothing and would have to have started from scratch, which would take a lot more time (the Poles had done their research in peace time) and significantly increased the chance of being discovered, which would have undoubtedly lead to changing the system, putting them back to square one.

      2. Basically they had built up a vocabulary over time via several means, including theft and subterfuge, aided by the general laziness of German cypher clerks who overused codes for common words. This was coupled with a familiarity of the formal structure of German diplomatic communications, and a deep understanding of the language itself. Armed with this, and good general idea of the topic of the intercept inroads could be made and the more this was done, the better they got at it as more of the encoding was exposed. The process was more akin to solving a word puzzle than decipherment per se.

          1. Wikipedia’s entry:

            “In Room 40, Nigel de Grey had partially deciphered the telegram by the next day. Room 40 had previously obtained German cipher documents, including the diplomatic cipher 13040 (captured in the Mesopotamian campaign), and naval cipher 0075, retrieved from the wrecked cruiser SMS Magdeburg by the Russians, who passed it to the British.

          2. I think the message was sent to their embassy (or German Legation) in Mexico City. The spies they sent there could have the code-book sent over in the diplomatic pouch by courier. Nobody gets to look in the DP. Only the intended people. Same applies today. I imagine it had a big swastika on it. Even you wouldn’t tamper with that as the courier is handcuffed and armed (and has diplomatic immunity). Then the spies would deliver the message to El Presidente. And this was his response. But he called it “badges” for some strange reason:

          3. Oops! I should have said MALTESE CROSS not SWASTIKA. Different timeline. Also the courier with the code-book may have actually been one of the German spies who received the Zimmerman Telegram, deciphered it, and delivered it to El Presendente. I still think the spy received it via the Telefunken wireless set aboard a secret U-Boat stationed in the Gulf of Mexico between Tampico and Veracruz. That would just be about 1.5 to 2 hour car drive to Mexico City (153 mile – 247 km). I would think the USA spies were watching this area for POTUS Wilson already as he had his eyes on the oil fields at Tampico and had already invaded Veracruz in 1914. So just like in an old black & white movie, the U-Boat was flashing semaphore to the German agent with a torch (aka flashlight) on the beach at night:

    1. How so? It doesn’t reflect Mexico in any negative fashion that I could tell. Honestly it shines a poor light on the US considering how poorly we’re handling our relations with Mexico at the moment.

  1. I really hate agreeing with [rutigrem], but come-on!

    …was partially decrypted by the people in Room 40.

    How?!? There is a serous omission in this article! At the least, an explanation of how they might have decrypted would have been nice.
    Did they use a RasPi? Maybe an Arduino? Of course not, they had rudimentary number crunchers where a ‘bug’ actually meant an insect stuck in the computing parts. And the amount of work that must have been done by hand, actual paper and writing utensil, must have been staggering.

    1. It was undoubtedly a group of unsung women at Bletchley Park. Yes that place dated back to WW1. It seems women have a propensity for numbers as can be seen by this new movie about NASA women. We dudes seem to be too dumb to even balance our checkbooks. Women have this Professor John Nash “Beautiful Minds” ability. They can see patterns in numbers. Must of us just see a bunch of frickin’ numbers and go – pffft… I don’t have a clue what that means! Hey Chuck can you dig that fly out of the computer’s gears? And oil it when your done… :-)

        1. @Lufo – I don’t know exactly what your asking is a joke. Do all women have this ability – NO. It just appears that statistically speaking you find more females have this mental ability than do males. Some males have this ability too like the late Dr. John Nash. The Brits used women for code-breaking in WW1 and WW2 at Bletchley Park. I imagine there were some men there too. Maybe I was joking about men being dumb. That was tongue-in-cheek humor. We’re not so dumb after all.

      1. Yeap …
        Like the Naval Enigma Machine “captured” from a meteorological Nazi vessel …

        The code was well and truly broken but they were unable to decode fast enough to be of any military use … hence getting the Naval Enigma little box from an enemy’s vessel.

        Too simple, really. They call that military intelligence. The real one, that is.

  2. Another bit of background. As soon as the war began in August 1914, the British severed all telegraph cables from the continent that Germany could use without going through the UK. It then allowed messages from Europe, including Germany, to pass through the UK’s cables. That gave them the encrypted texts, which they then needed to break.

    A reminder to Trump haters and their opposites. This website is about hacking not politics. Let’s keep in that way.

  3. So we’re just assuming the telegram was authentic and not fabricated by the British in the first place?

    How hard would it be for the Brits, who were pushing hard for the USA to finally enter the war, to initiate this?

      1. Why do people today always under estimate trade-craft from 100 years ago? Those boys and girls were just as full of stealth and guile as we are today. Yes we have more ingenious gadgets than they did but they had some pretty cool gadgets too. Mainly weapons. You’d be astonished how sophisticated the trade-craft was even way back to George Washington’s spies. The codes and ciphers were equally cool. The Jefferson Cipher Wheel “might” blow your mind if you were normal (just kidding Whatnot!) :-D

        The Mexicans ain’t sayin’ nuttin’ these days like Simpson’s Johnny Tight Lips. Can you blame them?

    1. This was my first thought as well, but I imagine that both the German Government and Zimmerman himself confirming the authenticity of the telegram (which they did), were enough to put to rest any doubts.

    2. So, lets go with them injected a fabricated telegram message. They can’t do it on the US to Mexico leg. The German ambassador in Washington is the one who retransmitted it, and would know it was a fake. So they have to do it on the trip from Germany to Washington. The problem is, it was actually originally transmitted from the American Embassy (because we had allowed the Germans to use our telegraphs for diplomatic messages). So if they compared the telegraph logs on the different sides, they’d have realized it was a fake.

      Regardless, Zimmerman acknowledged it was authentic, and since he was the German Foreign Secretary, it’s all over.

    1. With the Panama Canal at the time being under POTUS Roosevelt’s command & control, I doubt if Germany (The Kaiser) could have moved enough of it’s sea assets into place secretly to launch an offensive on California. They would have gone different longer very dangerous routes so as not to be discovered by USA setting up off our west coast. That would have over-taxed fuel and other resources. Imagine a German flotilla rounding the Horn. You think our Patagonian allies wouldn’t notice and warned US? Also Japan was on Britain’s side and had impressive sea assets all the way to Malta and South Africa blocking any German flotilla getting to the Western Pacific undetected. And a German land assault is purely outlandish. Also an air attack from a Mexican-German airbase wasn’t happening either. So there was no way for them to capture California even in their wildest dreams. Now Japan would have loved Hawaii or Alaska but they were not US states at the time. But the Kaiser wasn’t offering something he couldn’t have. He did have territories in Western Pacific like in China and elsewhere. Japan was not Germany’s friend at the time. They wanted all of Germany’s Pacific territories instead. They declared war on Germany 23 August 1914.

    1. It was NOT the main reason for WW1, that was little Gavrilo Princip “popping a cap” in the Arch Duke and his wife from a street corner as the limo was backing up. Kinda’ like a Chicago (USA) street thug today huh? The sinking of the Lusitania by U-39 with Tesla’s new water turbine engine and Tesla’s new wireless radio is what caused US to enter the war. They were informed By Sayville NY wireless radio of it’s departure from NYC en-route to Ireland. The U-39’s code word was “Get Lucy”. Also the message for Mexico to invade USA was a big driver for US too.

        1. A very messy and pointless war. Some call it the GREAT WAR. I have a sinking feeling that we aren’t done yet with such foolishness. With the latest events in USA I believe we are pretty much guaranteed some sort of ugliness soon. I have this creepy feeling it will start somewhere in the Levant and maybe even simultaneously Western Pacific as well. I wonder what the big US think-tanks are projecting…

          можемо тврдити, али и даље пријатељи. ок? :-)

          1. US has no business intervening past their own borders. They have much more important internal issues to deal with. Like large internal and external debt, money with no gold backing (since 1970.) being printed as toilet paper, death of American manufacturing, etc. Твој српски није нарочито добар, зато што Гугл транслејт често избацује глупости. Therefore stick with English.

          2. @Miroslav – Unfortunately I have to agree with you as to your assessment of my country. I’m not a goldbug but we stopped backing our dollars with gold in 1971. Not for the lack of knowing where gold deposits still exist in USA today. As there are many undocumented locations that are kept secret. I don’t think we are printing toilet paper as we have other valuable resources to back it up with.

            I agree with you that our American manufacturing is mainly overseas or Mexico today. We don’t even have any TV’s made in America. RCA in NJ was the last I think. China and Taiwan is really kicking our butts on that. However, our rich fat-cats are profiting from offshore outsourcing and don’t have any REAL plans to return stuff back to USA even despite our new Liar-in-Chief promises. He’s the biggest offender!

            I think the only way to get our economy back on the road again is for him to start a pointless war and our Military Industrial Complex will give him a standing ovation like he got a couple of days ago in Mclean Virginia. His sweetheart deal with Martin-Marrieta to build his idiotic wall to keep Mexico out will be sweetened by another war as MM (et al) will profit that too with US defense products.

            OK I know my Serbian sucks! But you got what I was trying to telegraph you right? Also I think it pretty much confirms to me that you are not Russian… ;->

  4. Well maybe there was a FOURTH option. Not sure how the Zimmerman Telegram was actually transmitted, either by transatlantic cable or the really brand new wireless station at West Sayville NY built just for the WW1 German spies. The Mexico attack message was sent from there. Also the U-Boat attack message on the Lusitania was sent from there too. And guess who built the damn thing for them? Our favorite HaD pariah TESLA!!! Why do so many HaD’ers like him now???

    Even though Bletchley Park and Room 40 was British, we (USA) had it’s own code breakers in WW1. We had a clever op in NYC that was a “non official cover” operation for making codes for businesses but was actually the forerunner to the NSA. It was nicknamed “Black Chamber” or “The Cipher Bureau” or “MI-8”, It was run by Herbert Yardley. USA knew what Tesla was doing WHILE he was doing it. The young J. Edgar Hoover while at BOI (forerunner to FBI) was watching every move he made and documented it for POTUS Wilson. Still available at the FBI website. They also were watching this same German spies he was working for at West Sayville NY (Telefunken Station). USA did not want to be dragged into this war. But that didn’t hurt getting us involved.

    Too bad we didn’t have a big concrete wall built by Martin-Marrieta for our POTUS to stop them Mexicans! (Oops, I think I was supposed to just think that and not actually say it…) =P

    1. OK, we figured by now that you just hate Tesla. Get off of it, or you’ll soon start with a bogus proof that he was a German agent. Speaking German and other languages does not make you into a spy. Or you want to claim that A. Einstein was a spy too?

      “HaD pariah TESLA” – only in your mind.

      1. I don’t hate TESLA I just have pity on him as he was a strange duck with the wrong direction from his Hindu mystic peers. I never said he was a German agent. He was an “unwitting agent” just like someone here in USA is presently with the Russians. And no it’s not bogus. It’s on our FBI dot GOV website. How is that bogus? It wasn’t his language acumen that damned him. It was his vengeful feelings toward our USG for rejecting his crazy before-its-time gadgets. Come on we rejected Mr. Holland’s submarine in 1890’s because our War Dept were idiots back then. But now our present day nuclear submarines are based on them.

        We rejected the first wireless transceiver device by Dr. Loomis in 1864. We rejected Tesla’s mini-remote control war boat but now have the Israeli Raphael which is just a remake of Tesla’s boat. We rejected his death-ray device as it was too way out there. Now Russia and USA (et al) have DEW weapons like particle beam generators.

        Tesla well knew what the Kaiser was going to do with those water turbine engines as he took money (a reoccurring royalty). The Kaiser put them into his U-Boats (i.e. U-39) and used them on the Lusitania first. Then they used the engines on their German NAVY craft and sunk a lot of British and American vessels. When he built the West Sayville NY Telefunken station for the Kaiser, he knew what they were using it for as he probably was there in the booth when they were sending test messages to the U-Boats stationed off of LI Sound. He was also building his strange otherworldly gadget at Wardeclyffe in Shoreham NY and POTUS Wilson had it destroyed by USN sappers.

        No Albert Einstein proved to be a good agent for US not Germany. He warned us about Heisenberg and just how close Hitler was to at least a deuterium dirty bomb or even a full-on uranium nuke. Albert literally save our lives by writing that letter to FDR about Hitler and his scientist’s research.

        “HaD pariah TESLA” – only in your mind. No there are plenty of HaD folks who are NOT Tesla-fan-boys. They get disgruntled every time we mention Lil’ Nikky. (I can feel them gritting their collective teeth right now) :-)

        You should pay closer attention to every corner of HaD so you can see what others think about stuff like this. I use the EMAIL notifier and I see a lot of Tesla-dissent. Anyway I had to pegged as a Russian… Miroslav… My bad.. I didn’t know “you had a dog in this fight”? (American euphemism for patriotic leanings to something).

        1. Mr. Henry Ford is the one you are looking for, if you are asking for help with the German war effort. Re WW1, do you think that US government did not know about the German spies milling about? They arrested all of them when war broke out. Tesla was buried with full honors, as American citizen. Why? Because he deserved it. You are barking up the wrong tree.

          1. Oh I agree with you Miroslav… we had PLENTY of American traitors in very high places back then and during WW2 as well (and apparently even today too). And yes many of the German spies in this particular conspiracy were rounded up. Some got clemency as they had friends in high places.

            Yes there is plenty to thanks to Tesla, as we wouldn’t have AC in our houses and other cool stuff. But you can’t just over look J. Edgar Hoover’s dossier on Tesla. It was an indictment on him based on his angst-ridden revenge against US for rejecting his earlier strange ideas to the US WAR DEPT (Ostensibly by Russell Alexander Alger 40th US Secretary of War and POTUS McKinley both short-sighted US Civil War men). He even admitted that was the reason he did that stuff. He tried to dress it up like an “education to the evil world” crap. Like a black-hat hacker breaking into a system just to prove a point that your security sucks. That’s not a valid reason to betray your new found country.

            Everyone is not privy to what Tesla did in the shadows. It was classified. But not any more. Also there is new light on Tesla’s NY hotel room so-called “natural death”. There was a death bed confession from a WW2 NAZI operative in USA in 1999 as to what really happened that fateful day and who actually got to Tesla’s safe. His name was Lt-Col Otto Skorzeny and Reinhard Gehlen. Both of their Wikipedia date of deaths were fictional.

            If you want to read the FBI’s dossier on Tesla you can find it here, it’s quite large. However, they don’t mention the murder in the hotel in 1943. Or maybe they did in their own way. They don’t mention those two NAZIS I mentioned.


  5. Mexico was in no position to try to accept that offer. The telegram was sent in 1917, seven years into the Mexican Revolution. Mexico would not end the Revolution until 1920.

    1. It probably wasn’t because they didn’t want to. It’s just that Germany had those goons in Mexico City and the Mexican president Venustiano Carranza knew they were the wrong horse to back in this war. They weren’t stupid like the other Central Power nations that knuckled under to the Kaiser. They wanted to remain neutral and they did. They were in the midst of their own civil war. And POTUS Wilson invaded Vera Cruz in 1914. They also knew Wilson had his eyes on their oil fields at Tehuantepec Isthmus and Tampico oil fields which produced 55 million barrels of crude by 1917. So Presidente Carranza decided to set the fields on fire instead of getting another invasion by Wilson and his General Pershing. Wilson was just looking for any excuse. So they remained neutral. That also pissed off Wilson.

      I agree with the poster who said the telegram was probably bogus. The Brits cut the Atlantic cable from Germany and re-routed it to UK (probably Bletchley Park?). Then the Germans sabotaged the UK cable. Probably PM David George concocted it and knew the MI-8 boys in USA would decode it too and really piss Wilson off again hoping it would cause him to jump in the fight. The Tesla transmitter at West Sayville NY for the Kaiser is what did it for him I think. The temerity of Tesla to do what he did and was also the fellow countryman of Gavrilo Princip who arguably started the whole WW1 thing… well the rest is history as they say…

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