The Zimmermann Telegram

zimmerman telegraph


By early 1917 the First World War was a stalemate. Germany had known, perhaps from as early as 1915 that it could not achieve an advantageous peace through its efforts on the Western Front. The German High Seas Fleet had remained in port ever since Jutland. There were growing food shortages at home.

The position was not much better for the Allies. Both England and France were on the verge of running out of money, and faced the prospect of asking for financial help from the US, which would come at the price of forcing them to start negotiating with the Germans, a prospect that neither side wanted.

So, something had to give, and the episode that probably tipped the balance was the message known as the Zimmermann Telegram, the greatest cryptological triumph of the First World War.

The telegram was sent in code on 16 January 1917 by the German foreign minister, Arthur Zimmermann, to his ambassador in Washington, Count von Bernstorff, with instructions to forward it to the German Embassy in Mexico. Decrypted, it translated as follows:








Second telegram

A second telegram was sent on 5 February 1917, this time directly from Zimmermann to von Eckhardt, the German ambassador to Mexico. It instructed him to open negotiations with the Mexicans and Japanese without waiting for a US declaration of war. This telegram was never made public until after the war.

We’ll come back to the detail of these messages in a moment.

Codes and Ciphers – is the difference clear?

At this point we perhaps need to understand the distinction between codes and ciphers, although the two terms are often used interchangeably.

Ciphers rearrange letters or change individual letters into a different letter, number, or a symbol based on a prearranged setting known as a key or keyword.

As a simple example of a Cipher, let’s take Playfair. This was explained in the Field Service Pocket Book, with which officers were issued in 1914, and there is also an instance in a Dorothy L Sayers novel, Have His Carcase, first published in 1932.

Briefly, you create a 5×5 square, think of a keyword, as long as possible, but without repeated letters. Put this into the square and fill the remaining cells with the unused letters. Split your message into digraphs, and use the two letters opposite them in the square as the message text.

On the other hand, codes change entire words or phrases into other words, number groups, or symbols based on a list or a book, and usually created by some form of arbitrary substitution. For example, in the case of the Zimmermann telegraph, the group 67893 indicated ‘Mexico’, and would always do so in that code. To decrypt the secret message, the receiver usually needs access to the original key list, or book. Examples of codes are road signs and, of course, the ubiquitous bar code.

How you get hold of the code varies. For instance, in the 1920s, US Naval Intelligence funded some FBI break-ins at the Japanese Consulate in New York, primarily with the aim of detecting subversive activities, but in the course of which they photographed the entire Japanese Fleet Code Book [NSA]. If you can’t acquire the codebook or a copy, solution of a code may have to rely on operator errors, the context in which it is used, which may produce depths, and, of course, a certain amount of luck. The British had at least two such instances that relate to the Zimmermann telegram.

The first was that the Russians had acquired some German codebooks as a result of their destruction of the cruiser Magdeburg on 26 Aug 1914 in the Baltic. They thought this material would be of more direct use to us than them, and we duly sent a ship to pick it up.1 Not only did the material contain the word columns from which the code was derived but also a cipher system used to vary the code from time to time. This was of extreme value in that it helped Room 40 (who were still novices at this point) to understand how the systems worked, which would help in breaking other naval systems. They also received material from the Australians and as a result of a lucky find by a British trawler.

  • 1 Kahn, quoting Winston Churchill. Tuchman says it was sent in a Russian fast

The second concerned a character called Wilhelm Wassmuss. He had been German vice-consul at Bushire (on the eastern coast of the Gulf) and had had a number of escapades with the British and Persians in his attempt to foment disorder; he was a sort of Persian version of Lawrence of Arabia. In the course of his travels, his luggage had been seized by the British and he spent an inordinate amount of time and energy in trying to get it back, even complaining formally to the local Persian Governor. This signal traffic came to the attention of Room 40 in London, who asked the obvious question. Where was this luggage now? It turned out that it had been sent to the UK and was in the basement of the India Office, just up Whitehall from the Admiralty. It was ‘liberated’ from there and found to contain a copy of the German diplomatic code 13040. No wonder he wanted his baggage back. I can find no evidence (albeit from limited research) to suggest that he reported the loss to Berlin – perhaps understandably.

Let’s look at some of the others involved in this story.

Blinker Hall and Room 40

Originally located in Room 40 Old Building (of the Admiralty) this element of naval intelligence (more properly designated NID25) was headed from October 1914 by Captain (later Admiral Sir) Reginald Hall, who, because of his tendency towards excessive nictitation, had acquired the nickname ‘Blinker’. He has been described as ‘a demonic Mr Punch in uniform’ (Kahn, p. 133). The US Ambassador in London would later describe him as a genius, against whom all other secret service men were amateurs (Kahn, p. 134). Died 1943, aged 83.

He expanded the scope of operations beyond the naval sphere, and began to look at diplomatic traffic, partly because naval traffic was greatly reduced after Jutland, but also because there was no one else to look at it. His greatest achievement was undoubtedly being able to exploit the opportunities offered by the Zimmermann telegram, without compromising its source and how effective the British were at cryptography.

Although they later moved to larger premises, the name Room 40 OB stuck, and it’s how they will be referred to from now on. By the end of the war, it was estimated that they had decrypted some 15,000 messages (14 October–19 February), an average of about nine a day) (Kahn p. 133, 1967).


Arthur Zimmermann was unusual in that he was the first non-Junker (i.e. no Von in his name) to be appointed state secretary (aka foreign minister). Because of his more humble origins he started in the consular service, with his only foreign posting being to China in the late 1890s. He returned via North America, which should have given him some feel for the industrial might and assets available to the US. It has been claimed that he declined to apply for the post of foreign minister when it became vacant in 1912 because of his weakness in foreign languages, and his inability, as a commoner to hold his own in Berlin society (Bogart p. 5). He was appointed state secretary on 22 November 1916.

He was consumed with a desire to always do the right thing by his bosses, which may be an admirable trait at times, but does limit the capacity for making independent judgements. His appointment was welcomed by the US, where one newspaper headline described him as ‘Our Friend Zimmermann’ and claimed that ‘all Americans like him’, so they must have thought that he would bring a more liberal and democratic approach to German foreign policy. They were wrong. Zimmermann wanted to be more Hohenzollern than the Kaiser and was desperate not to offend the powers that ruled Germany at the time, notably Hindenburg and Ludendorff. As one observer put it, Zimmermann always ‘swam with the stream and with those who shouted the loudest’ (Tuchman, p. 109). He was, in the eyes of the military, an ideal candidate because of his natural inclination to obey orders.

However, Ludendorff’s belief that Zimmermann would follow him blindly was misplaced. When Ludendorff tried to have Chancellor Theobald von Bethmann- Holweg replaced to clear the way for submarine warfare, Zimmermann backed the chancellor. The military threatened to resign if they did not get their way. Ludendorff outmanoeuvred the civilians by taking advantage of the fact that the civil government and military headquarters were geographically separate, the latter being in Pless, in East Prussia (now Pszczyna in Silesia, and part of Poland). Zimmermann was summoned to Pless in early January 1917, and, although there are no written records of their talks, probably received a thorough dressing down from Ludendorff over his failure to support unrestricted submarine warfare. Ludendorff would later say that he felt Zimmermann was ‘dishonest’ and it would not be long before he ‘demanded his head’.

This, of course, put Zimmermann in a very uncomfortable position both psychologically and politically. The chancellor had been bullied into accepting unrestricted submarine warfare, and Zimmermann had clearly backed the wrong horse. He had to realign himself with the military as soon as possible. It was in this climate that the plan to ally with Mexico and Japan was devised.

Woodrow Wilson

Woodrow Wilson became US President in 1912. His background was in academia, but he had been Governor of New Jersey. He had been elected with the intention of making extensive domestic reforms, but said at the start of his term that ‘It would be the irony of fate if my administration had to deal chiefly with foreign affairs’ (Tuchman, p. 38), which, as things turned out, was a masterly understatement.

He was someone who tended to have his own views on most things, and not necessarily agree with or listen to advice that he might be given. He treated his ambassadors as messenger boys, expecting them not only to pass on his policies, but also to agree with them. He had been re-elected in 1916 as ‘the man who kept us out of the War’ and was determined to stay neutral and to get the belligerents to negotiate on his terms, a fond hope given that it would mean a ceasefire and then talks, with both sides remaining in situ. He would also be looking for what we would now call ‘regime change’ in Germany. This was obviously unacceptable to Berlin, and to the Allies, who wanted Germany off their territory. An impasse was inevitable.

Wilson, however, continued to hope. His reaction to the German decision to resume unrestricted submarine warfare was to break off diplomatic relations. His policy was to wait for an ‘overt act’ (undefined) to occur before considering further action. This put him at odds with his cabinet who, with the exception of Josephus Daniels, a pacifist and unusual choice as secretary of the Navy, were what we would now call ‘hawks’. (Died, after a stroke, in 1924.)

Returning to the text of the telegram, it mentions Mexico and Japan.

Why Mexico?

Mexican–US relations had always been problematic to say the least. A war in 1848 and subsequent treaties over the years had led to major losses of Spanish or Mexican territory to the US. From 1876, the country had been ruled by Porfirio Diaz, who summed things up well: ‘Poor Mexico. So far from God and so near the United  States’ (Tuchman, p. 65). The ‘modern’ era in Mexican politics might be said to have started with Diaz’s overthrow in 1911 by a movement begun in 1910 and led by Francisco Madero, who promised better conditions for the peons and more democracy which, in the eyes of the Americans at least, made him a ‘good guy’.

Unfortunately good guys don’t last, and within two years Madero was arrested and then murdered, almost certainly on the orders of General Victoriano Huerta.

Wilson had taken office in 1912, and had high hopes for Madero. When he was killed, Wilson saw Huerta as a usurper, and would do nothing to help him.

There continued to be a power struggle in Mexico, with Huerta facing opposition  from Venustiano Carranza and Pancho Villa, who were Madero supporters (known as maderistas).

There were a number of incidents which hardly helped foster good US–Mexican relations. In April 1914 nine US sailors were arrested in Tampico. They were released, but the US Admiral demanded not only an apology, but also a 21-gun salute to the US flag. The apology was not a problem, but the salute was denied. Amazingly, this escalated until it reached Wilson, who now found himself in a crisis from which there was no easy way out. Huerta would argue that he should not be required to salute a country that did not recognise his regime. After several deadlines had expired, Wilson decided to ask Congress to authorise force, despite everyone feeling uncomfortable that it was all about a salute.

Meanwhile, Germany had offered help to Huerta, and the Americans learnt that a German ship would shortly be docking at Veracruz with an arms shipment. Wilson now acted and ordered that the ship be stopped and the customs house in Veracruz seized in order to prevent any arms being landed for Huerta or anyone else. This was on 21 April 1914. US Marines and sailors duly landed. Wilson would claim that this action was ‘to serve mankind’. No one told the Mexicans, who resisted. By the time the operation was over, some 17 Americans and 126 Mexicans had been killed, and  71 Americans and about 95 Mexicans wounded.2

Then the Germans complained about the halting of their ship in the absence of a formal declaration of blockade. State Department lawyers confirmed that the Germans were in the right, and the US Admiral was ordered to apologise personally to the ship’s captain.

The Germans welcomed the incident, which led to much anti-American feeling throughout South America. The ABC powers – Argentina, Brazil and Chile – offered to mediate. It was too late for Huerta, however, as Carranza was able to overthrow him, and he went into exile, to reappear later, with German backing.

In October 1915, the US recognised Carranza’s government. The reasons were simple:

  • Germany wanted US intervention in Mexico: therefore they must not intervene;
  • Germany did not want one faction to be dominant: therefore the US must recognise one;
  • Relations with Germany were the first priority and thus dealing with Mexico must be regulated accordingly.

The US began to help Carranza, who had now split with Villa, by allowing Mexican military movements by US railroads in US territory. This enabled Carranza to conclusively beat Villa when he attacked, as he had been expected to do, at Agua Prieta, in November 1915. It broke Villa’s power and left him with a maniacal desire for revenge.

Columbus raid

There had been various acts of ‘terrorism’ involving Americans in Mexico, the worst of which being the murder of 16 engineers on a train in Chihuahua province. One survivor got away to tell the tale, which might otherwise have never been noticed. Nothing was done about it.

Villa’s next action was probably designed to destabilise the Carranza regime. On 9 March 1916, Villa and his men attacked the town of Columbus, New Mexico. Columbus might reasonably be described as a one-horse town, but for the presence at the time of the 13th US Cavalry. A firefight occurred, with casualties on both sides, including at least 16 American deaths.3

2 Figures vary. These are from Tuchman, p. 48.

3 Tuchman has 18 deaths. State Department archive says 16.

The raid caused an uproar, being a blatant incursion into US territory: Something Must Be Done. The result became known as the Punitive Expedition. Command was given to Brigadier General John Pershing over the head of the local major general, who was not well pleased. Pershing was given 6,600 men and told to find Villa. Now, Mao Tse-Tung said that ‘the guerrilla swims like a fish in water.’ Remove the water and the fish dies. Most of the local population merely wanted to avoid trouble and survive, but, whatever faction they might prefer, all were generally anti-American. As a result, Pershing and his men penetrated 500 miles into Mexico and found nothing. Communications were poor, and not helped by the Mexican hobby of shooting at telegraph wires. The fact that Villa could not be found was emphasised on 6 May, when he launched an attack on a military outpost at Glen Springs, Texas. Chased across the border, he got away. Carranza and the US agreed to set up a joint commission, which met in September, and issued a statement on 24 December stating that US troops could remain as long as it was necessary, but should otherwise withdraw. Carranza rejected it, as it implied a permanent US presence. However, the talks served to ease tensions and the US began preparations to leave. The main campaign lasted from April 1916 to late January 1917, and Pershing finally completed his withdrawal on 5 February (Note: same day as the second telegram was sent).

This was a small episode in US military history, but interesting nonetheless. It was the first use of motor transport by the US Army, and probably the first military use of aircraft. The latter were largely useless, as their engines were underpowered and unfit for hilly terrain. There was some improvement, with the air commander believing that they’d done a good job. Well, he would say that, wouldn’t he? There was also a radio intercept unit present, again a possible American first, but they would have had the same sort of problems with the terrain as did the aircraft. Have not found  any evidence of targets or success rates, and Villa probably didn’t have sophisticated comms or signals plans. I would suspect that the main use of radio was for direction finding. Interestingly, Pershing was allowed to choose his own staff. Amongst them was a Lieutenant George Patton (a cavalryman), who did rather well for himself in World War II. An NSA article claims that Patton was an enthusiastic user of intelligence, especially SIGINT, and this contributed much to his later success.

The effect of all this uncertainty meant that for much of the decade, some three-fifths of the regular US Army were tied up in the south-west of the United States.

Why Japan?

Japan was actually on the Allied side (having declared war on Germany), but was clearly looking to get more out of the relationship than they put in. They had acquired German territories in the Pacific, but had so far done little more to support the Allies.

There is evidence of trade between the two areas as far back as 1611, so contacts aren’t as unusual as you might think. More recently there had been rumours in 1908 that the Japanese had acquired a lease on Magdalena Bay, the largest and most secure base on Mexico’s Pacific coast, and one that the Kaiser had secretly tried to buy. There were also rumours of Japanese troops being in Mexico in disguise and of a secret treaty. It was, in fact, a German fabrication, created in the hope that the Americans would invade Mexico. Tuchman (p. 35) comments that ‘for the purposes of history, what actually happened is less determining of later events than what people think happened. Germany had succeeded not only in making Americans believe in the possibility of joint Japanese-Mexican action against the United States but making herself believe in it’.

A Japanese battleship had run aground in April 1915 in a Mexican bay (accidentally on purpose?). Reports continued of Japan planning naval installations on the Mexican coast, all of which were amplified by the German press. Japan didn’t mind – it could help them get more out of the Allies without having to resort to open aggression.

Japan had become suspicious of US intentions largely because of the immigration policies adopted by some of the states. California had banned Japanese citizens from owning or leasing land, and Idaho and Oregon were proposing similar legislation (Tuchman, p. 37, 146). The Japanese could not believe that the Federal Government could not overrule these laws.

Sending the telegram

The idea of an alliance was probably conceived by Arthur von Kemnitz, counsellor on Latin American and East Asian affairs in the Foreign Ministry, and one of Zimmermann’s closest advisers at this time (Boghardt, p8). It was approved by Zimmermann, who doesn’t appear to have consulted with the chancellor about it beforehand, or got his approval, which emphasises where the real power lay in Germany in early 1917, as well as perhaps Zimmermann’s desire to realign himself with the military. The Germans probably knew that the US was likely to withdraw from Mexico, and the timing of the telegram may have been an attempt to try and keep them embroiled there.

There were some differences between the message sent from Berlin and that which was eventually published. Perhaps the most interesting is the change from ‘generous’ to ‘general’. The original word was ‘reichlich’, which my dictionary translates as ‘ample’, ‘generous’.

So why the differences? The story goes back a few years before. Britain declared war at midnight on 4 August 1914. By early morning of that day the cable ship CS Telconia had torn up the German transatlantic cables, a move planned back in 1912 by the Committee for Imperial Defence. The cables in the Mediterranean were British-owned, and so could be controlled, leaving just one from Liberia to Brazil, which was cut thanks to a few favours being called in (p. 8-9).

This meant that the only way that Germany normally had to communicate with the rest of the world was via a transmitter at Nauen, outside Berlin. This, of course, meant that the messages could be intercepted.

The original intention had been to send this message by submarine, but, fortunately for Britain, it proved impractical because of the time involved. Zimmermann couldn’t deal directly with the Mexican Ambassador, who was resident in Switzerland. To ensure delivery he routed his telegram not only via Nauen, but also used two other ways, both of which were known to the British. Room 40 knew the first one as the ‘Swedish Roundabout’. Sweden had been helping the Germans get messages past the British cable blockade from 1914. Their cables touched England, and so could be monitored. When they complained in 1915 that their cables were being delayed the British told them they had positive proof of this breach of neutrality. The Swedes promised not to send messages to Washington. Instead they sent them to Buenos Aires, from whence they could be forwarded to the US, a route of about 7,000 miles, largely violating their prerogatives as a non-belligerent. (p. 137). Room 40 found this out (thanks to a stream of messages trying to get a high German decoration for the Swedish chargé d‘affaires in Mexico City (p. 99)) but did not protest, as it was more advantageous to be able to read the traffic (p.137).

But perhaps the cheekiest route was described by Kahn (p. 137) as being ‘of such simplicity, perfidy, and barefaced gall that it probably remains unequalled in the annals of diplomacy’, and which Tuchman said required a willing suspension of disbelief. It was using the Americans. Remember that Woodrow Wilson wanted peace negotiations, and when the Germans claimed that they could not communicate securely with their Embassy in Washington to discuss peace proposals and offers, he allowed them to use US diplomatic channels to send their messages. This was the result of an arrangement brokered by the President’s adviser, Colonel Edward House, a man never likely to overestimate his own importance. It so appalled Secretary of State Robert Lansing, that he had to be given a direct order by the president each time it was proposed to use this route, at least for traffic from Washington. Not only that, but the Germans obtained permission to send telegrams in code or cipher, rather than in clear as common sense and most neutrals would require.

Additionally, but fortunately, there were two different codes involved in getting the message through to Mexico. It was first sent to Washington using code 0075, a relatively new one, first distributed in July 1916 to various missions in Europe and Turkey, and to the US by submarine in November, from whence it was seen in Washington traffic. Initially, only partial solutions were possible (Kahn p. 1351). Mexico did not have 0075 yet, so Washington re-encrypted it using code 13040, which, as noted above, had largely been recovered by the British thanks to Wassmuss and his exploits.

How to release it?

It took until 19 February for Room 40 to fully decode the telegram (Tuchman p. 154). Initially Hall had thought, as had some US diplomats in London, that the public announcement of unrestricted submarine warfare would lead the US to declare war. Hence he delayed in letting the Americans see the message. However, Wilson’s only reaction was to break off diplomatic relations. He said that only ‘overt acts’ of hostility would lead him to do more (although quite what form these might take was not specified).

Hall’s problem was how to release the text of the message without compromising British codebreaking efforts. His solution was to try and get a copy of the telegram as sent by von Bernstorff to Mexico. This would, he hoped, have some detail differences from the text originating in Berlin, since he wanted the Germans to believe that it had been intercepted somewhere in the Americas.

This he managed to do, and used this copy when dealing with the Americans. As expected, there were small differences – serial number, preamble, date, as you would expect with something being forwarded.

It was shown first to Hall’s contact at the US Embassy, and then to Walter Hines Page, the ambassador. They decided that, as a first step, the British Foreign Secretary, Balfour, would hand it formally to the ambassador (government to government). The Americans could then locate in their own Western Union files in Washington either the incoming telegram to von Bernstorff or the one he forwarded to Mexico. The code groups could be telegraphed to London, and the message decoded, with the help of Room 40 and the codebook, in the American Embassy. This would provide convincing proof of the authenticity of the message.

Balfour gave the telegram to Page on 23 February, and it reached Washington the next day, along with an explanation of why it had taken so long, and giving no further detail about its acquisition as this might endanger lives.

Reaction in US

When he first was told about it, Wilson initially wanted the telegram published, but was constrained to wait until confirmatory information could be obtained from Western Union. Once this was acquired, it was decided to release the message to the Associated Press, who broke the story on 1 March. As requested, the British were not given as the source of the telegram. In fact, a cover story was devised stating that no information about the source could be given as it might endanger lives.

Wilson was deeply shocked by the revelation, especially, no doubt, by the realisation that he had been duped by the Germans. The custodian of his papers, Ray Stannard Baker, believes that ‘no single more devastating blow was delivered against Wilson’s resistance to entering the war’ (Quoted by Tuchman, p. 193).

Initial reaction to the telegram elsewhere in the States was a mix of shock and disbelief. ‘Profound sensation’, noted Lansing. The not inconsiderable pro-German press, especially in the Midwest and the Hearst newspaper empire believed it was a British plot. The people in the southwest were outraged. (Remember what Tuchman had said, quoted earlier: ‘for the purposes of history, what actually happened is less determining of later events than what people think happened’.)

However, there still remained a considerable degree of doubt in some circles about its authenticity, which could have been overcome by the exposure of the second telegram. As already noted, however, this was never mentioned until after the war. It would have revealed too much about British cryptological success.

Reaction in Mexico and Japan

Mexico set up a commission to examine the feasibility of the German proposals. It can’t have taken them long to dismiss them. They could never defeat the Americans militarily, the offer of ‘generous’ help was dubious, and even if they were to recover the three states, they would be faced with a hostile English-speaking population, leaving them with a considerable internal security problem to manage. The fuss scared Carranza off, and von Eckhardt had to tell Zimmermann on 14 April that Mexico had decided to remain neutral.

The Japanese dismissed the whole idea from the start as laughable, although doubtless recognising that it could be a useful piece of leverage to get more from the Allies without much effort.

Acknowledgement of authorship

The pro-German lobby in the US continued to denounce the telegram as a British plot. But then Zimmermann did something strange. On 3 March he held a press conference, and was asked by William Bayard Hale, a US reporter later shown to be a paid German agent, about the message. ‘Of course’, said Hale, trying to give Zimmermann an out, ‘your Excellency will deny this story.’ Zimmermann replied ‘I cannot deny it. It is true.’ He would again admit it before the Reichstag on 29 March, but lied, claiming that Carranza would have known nothing of the proposal before the Americans revealed it.4

Zimmermann’s admission of authorship really set the cat among the pigeons. ‘They mean us!!’ was a typical headline. Most German–Americans shifted their allegiance  to the right of the en dash (although, in fairness, many thought themselves more American than German). It confirmed the Eastern press in its Anglophile views, and led to a shift in policy by the more pro-German publications, some of whom had staked their reputations on it being something cooked up by the perfidious English.

The telegram also provided Wilson with his ‘overt act’, and whilst he clearly didn’t want to go to war, probably now felt pressured by public opinion to take a more aggressive stance. He had already tried to arm merchant ships, but the proposal fell foul of Congress. Now he had something more positive, which would allow him to act without compromising his earlier position.

On 2 April Wilson addressed Congress to ask them to declare war. He mentioned submarine as eloquent evidence. ‘We accept this challenge of hostile purpose …’

  • 4 Despite being given a vote of confidence, Zimmermann would lose office when the chancellor’s government fell four months later (5 August 1917), with his career over. (Died 1940, aged 81). (p, 190).

So war was declared, and the rest, as they say is history. But there’s a tailpiece to this story.

German inquiry about how message obtained

Not surprisingly, the Germans wanted to find out how the telegram was revealed. They were successfully misled by Hall starting rumours that the leak came from Mexico. Kahn describes how Eckhardt was bombarded with messages from Zimmermann wanting to know the arrangements for handling such messages. Eckhardt, who was, of course, innocent, was not going to take the blame. He described how messages were handled by Magnus, the embassy secretary, who brought them over to the ambassador at night, and read them out to him ‘in a low voice’. His servant, who did not speak German, lived in an annex to the residence.

Berlin conducted a more thorough inquiry, but never considered that the British might be reading their codes. Perhaps they thought anything devised by them was foolproof. Their report appeared in the Cryptologic Quarterly of Spring/Summer 2001, and is available on the NSA website. It makes fascinating reading. For instance, it admits: ‘safeguarding of the codes in Washington was not especially secure; they were  located in an older cabinet that was locked only with a combination lock that was already somewhat worn out. The combination had not been changed since 1902. When a combination lock is well worn, even a non-specialist, if he’s lucky, can correctly dial the combination by feel. It also wouldn’t have been difficult in the summer, when the embassy was in the countryside, and very few personnel remained behind in Washington, to slip into the chancery spaces, remove code 13040 from the code cabinet, photograph it, and put it back again. Code 13040 was located in Washington during the summer in 1915 and 1916’.

Effect of the Telegram

It is generally accepted that the US would have entered the war sooner or later, but just when is impossible to say. The main impact of the Zimmermann telegram was to get the rest of the US involved. Whilst the war was far away, the only people who might show some interest were on the East Coast. With the telegram suggesting that the South-West and West Coast might be threatened, the rest of the country awoke to what was happening. Consequently, there was greater support for a declaration of war (although it was by no means unanimous)5 than there might have been if the only ‘overt acts’ had been the sinking of US vessels, and it would have been far harder for the administration to drum up some enthusiasm for taking any form of military action, whether arming merchantmen or going as far as to declare war.

This was the real significance of the telegram, and why it can justifiably be called the greatest cryptologic feat of World War I.

5 In 1917 the Senate voted 82 for war, with six against. House was 373 for, 50 against. Most opposition came from the West and Midwest. In 1941 there was only one dissenter, Representative Jeannette Rankin, (R-Montana), a pacifist who had also voted against war in 1917.


Tuchman, B W (1958, rev 1971), The Zimmermann Telegram, Bantam Books, New York.

Kahn, D. (1967) The Codebreakers, Sphere Books, London (1973 edition).

[Redacted], (2001), The Zimmermann Telegram, Cryptologic Quarterly, Spring/Summer, NSA, Fort Meade, MD. Referred to as [NSA] in text.

Boghardt T (2003), The Zimmermann telegram, Diplomacy, Intelligence and the American Entry into World War I, Working Paper Series, BMW Center for German and European Studies, Georgetown University, Washington DC.

Johnson, J (1997), The Evolution of British Sigint 1653-1939, GCHQ, Cheltenham.

National Cryptologic Museum – Exhibit Information 2014, NSA, Fort Meade MD.

United States occupation of Veracruz, Wikipedia, last accessed 11 Jul 2014.

Yockelson, M (1997), The United States Armed Forces and the Mexican Punitive Expedition, Pts I & II, US Archives, last accessed 14 Jul 2014.

Failed      Diplomacy:      the      Zimmermann      Telegram,      Resources4Educators,

//education.Texashistory.edi, last accessed 10 Jul 2014.

Punitive Expedition in Mexico 1916-1917, US State Department archive, www.2001-, last accessed 12 May 2015.

Glenn Springs Raid, Texas State Historical Association,, last accessed 15 May 2015.