The History and Mathematics of Codes and Code Breaking

The Truth Behind the Zimmerman Telegram

In 1917, during the height of World War I, the British intercepted a German telegram (the Zimmermann Telegram) that was meant for the Mexican government.  The Germans called for unrestricted submarine warfare, which violated a previous agreement with the United States, and proposed that if Mexico invaded the United States, Mexico would receive United States territory at the end of the war.

In high school history classes, we are told that as soon the British caught word of this duplicitous German telegram, the United States' government was immediately notified.  However, as Singh explains in the third chapter of The Code Book, the British initially withheld the information, at the potential cost of American lives due to unrestricted submarine warfare, in order to protect the cryptographic advancements of the British.  At first, I thought that the actions of the British were wrong.  The lives of innocent people were on the line.  Yet, I realize that from a broader perspective, the move to protect British cryptographic intelligence was ethical and necessary, because in the end, it led to the demise of the Germans and to the end of the war.

If the British had immediately informed the American government of the Zimmermann Telegram, chances are the United States would have publicly condemned Germany for its actions.  The success of the British codebreakers would have become known, and the Germans would have realized that their ciphers would need improving.  Had the Germans known this, they could have created a better, more impenetrable cipher, and the Allies would have been back at square one.  Since the Germans were unaware that their cipher had been broken (they believed that the Mexican government had handed over the telegram to the United States), the Allies had an upper hand, because they now knew the German code.

Overall, the British decision was ethical, because in the grand scheme of the war, more lives were saved by defeating the Germans than lives that would have been lost from unrestricted submarine warfare.  By protecting British cryptographic intelligence, Germany was blindsided and fell behind in their cryptographic advancements.  Because of this, Germany lost yet another advantage in the war.


Ethical yet Reasonable?


Ethically Relying on the Unknown


  1. Andrew

    As a summary, it seems that you're saying that it was ethical for the British to withhold the secret to German cryptography from the Americans because it, in theory, saved more lives by ending the war. I definitely agree that it saved more British lives, because it allowed the British to know when Germany would be attacking.
    However, I must point out that a lot of your arguments are very much lacking in certainty. If the Brits had informed the American government of the Zimmerman Telegram, the US may very well not have publicly condemned Germany. The US could very well have realized that this was an issue of national security rather than of publicity. It is likely that the US would not have gone public with their knowledge, and instead used the knowledge to secretly save American lives, and end the war even more rapidly. This is a point I think you'll find hard to refute with any certainty.

    • Derek

      Good point, Andrew. It's quite possible that the Americans would have kept Hall's secret. However, had they acted on the Zimmerman telegram by pulling their ships out of harm's way, the Germans might have suspected that their messages were being read. And that might have been enough for them to change their codes.

      One the challenges in analyzing this decision is that there are a lot of "probably"s and "might"s, as Colleen pointed out in her comment. And it gets especially hard to weigh such probabilities with the benefit of hindsight, knowing how things actually did turn out, given the decision that Hall made.

  2. Maria Sellers

    I have a hard time accepting Admiral Hall’s decision as ethical. It was certainly the most logical and strategic decision possible given the circumstances, however, no decision made by one person about which lives are worth sacrificing can ever be 100% ethical. Had Hall tipped off the Americans sooner, many lives could have been saved, but many lives would have been lost as well. Should the Germans realize that their encryption was no longer secure, they would switch to a new form of encryption that the British may not be able to break. Hall’s fear, as Singh says in chapter 3, is that “If the British gave the Americans the deciphered Zimmerman telegram, and the Americans reacted by publicly condemning Germany’s proposed aggression, then the Germans would conclude that their method of encryption had been broken” (Singh 112-113).

    Admiral Hall had no proof that the Americans would react publicly, any more than he had proof that the Americans would get involved in the war after the Germans went back on their word and began unrestricted U-boat warfare. In the case of the latter assumption, Hall was wrong. He underestimated how dedicated Wilson was to his policy of neutrality. In the end, Hall ended up handing over the telegram, but he orchestrated it in a way that made it appear that the Mexican government had handed the telegram over. Personally, I question why he was unable orchestrate this red-herring in order to turn in the message before the Germans began unrestricted U-boat warfare.

    The fog of war shows that most decisions are not black and white; they’re grey. In spite of this, it is never ethical for one person to decide whose lives can be spared and whose cannot. Sacrificing the few for the sake of the many can be the correct decision, and it can be the strategic decision, but it can never be a truly ethical decision. It is a decision purely based on logic and cost rather than emotion and empathy. I’m not saying that Admiral Hall made the wrong decision; as a matter of fact, I agree with him. However, just because it was the correct decision strategically does not make it an ethical decision.

  3. devandy

    Ethical dilemmas show themselves all the time in real life, and I believe that in this case, they are very similar to the trolley problem. The trolley problem is as follows: “Should you pull the lever to divert a runaway trolley that is on its way to hit multiple people, to hit a single person on another track?” Do you do nothing and let the trolley kill those multiple people, or do you pull the lever to kill one?
    Admiral Hall had to make a similar decision. In this case it was to provide the American government with information that could have saved many lives, or to keep it so the Allies could keep a strategic upper-hand on the Germans. Hall chose the latter because he thought it would be for the better, and indeed this lead to the loss of WW1 by the Germans, but what were the opportunity costs of this decision? Many more American lives could have been taken by German U-boats if they decided to attack more vessels that the Lusitania. In a sense, with this decision, Hall chose to sacrifice the lives of the few, for the better of the many.
    The above blog post states that this was an ethical decision, but by definition an ethical decision is one that deals with right and wrong conduct. No decision that includes taking the lives of innocent people should be considered ethical because taking human lives in itself is not ethical. Furthermore, he bases his decision on the assumption that America would automatically call out Germany with wages of war, thus driving the Germans to make a whole new cipher for their messages. This means the decision is even more unethical because these types of important decisions should be based on clear certainties.
    This leaves Admiral Hall with choosing a decision that has only damning consequences because there is essentially no ethical choice in the matter. However, I do believe his choice was the right one. As we can see now, it lead to the ultimate loss of WWI by the Germans. This just goes to show that sometimes, questions do not have to have ethical answers.

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