Betty Webb, one of the last members of the Bletchley Park circle which cracked Nazi ciphers, passed away this week at 101. From 1941 to 1945, she worked to help in the decoding of German messages and also worked on Japanese signals. The remarkable struggle she participated in helps understands how communication intelligence became the key to winning modern war.
New Delhi: Early on the morning of the 5th of May 1945, Admiral Karl Dönitz signalled to his battered sailors that the end of their war had come. The harbour master at the port of Oresund, Helsingor, told the commander of the submarine U-534, Herbert Nollau, that a ceasefire was in force south of the 56th parallel. He received orders to move to Skagerak in Norway and thus remain just outside the ceasefire zone.
Nollau decided to sail 2 miles north of that latitude, together with the U-3523 and U-3503. Two Royal Air Force (RAF) bombers spotted and attacked U-534 though, a submarine which had failed to score a single kill in the entire war. The submarine succeeded in shooting one of the two bombers down, but the other destroyed it with a depth charge.
500 miles away at a small hut in England, the movement orders, transit and death throes of the U-534, sent by its commanders using the most sophisticated encryption technology of the time, were being recorded in unsentimental detail: ‘Bomb hits on U-534 at 1338. Boat sank. Rescue operations in progress.’
Last week saw the passing of a magnificent lady called Charlotte Webb at the grand old age of 101. She was one of the hundreds of women and men who worked at Bletchley Park, the communications intelligence centre that broke Nazi Germany’s military encryption and arguably played a key role in winning the war.
Betty Webb MBE
It is with great sadness that today, the Bletchley Park Trust has learnt that Charlotte (Betty) Webb MBE has passed away at the age of 101. Her contributions to Bletchley Park, during World War Two and to ensuring its legacy today, will never be forgotten.… pic.twitter.com/Ybh6uTDUZH— Bletchley Park (@bletchleypark) April 1, 2025
She was one of the people who possibly saw that submarine’s death throes. But there’s a reason why this old English lady’s passing ought to be especially remembered. F.H. Hinsley, the author of an official history of British intelligence, as well as a remarkable collection of first-hand accounts of the Bletchley Park codebreakers, has estimated that cracking Germany’s Enigma code saved the Allies three to four years of war and huge expenditures in lives and resources.
Enigma’s movie version ‘The Imitation Game’ (2014), which many of you have seen and those who haven’t should see, centres around the legendary mathematician Alan Turing, who also laid the foundations of modern computer science. Lots of others, though, also deserve to be remembered and my story today will have something about them. Top credit should go to the brilliant Polish mathematicians Marian Rejewski and Henryk Zygalski, who not only succeeded in devising the mathematical methods that allowed Enigma to be decoded way back in 1932, but also laid the foundations for its eventual mechanical automatic decryption.
Then there was Dilly Knox, a British mathematician who cracked a commercial version of Enigma as early as 1937. And of course, there were those non-specialists like Webb, whose humble contributions were to index coded communications and prepare paraphrased summaries of the deciphered content. Even though Webb read through German police messages which revealed the beginnings of the Holocaust, studied Japanese war messages for the Pentagon and, of course, played a key role in protecting Atlantic commercial traffic against Nazi submarines, she never once spoke of it until 1975, hiding her work even from her parents, who passed away before she shared the story.
This week’s Explorer, though, isn’t just about Webb. It’s looking at the story from the other side of the mirror. The story, that is, of the people who created Enigma, the people who defeated it, and the Nazi communications intelligence services who also successfully worked to defeat Allied ciphers and codes.
This story isn’t interesting only because it’s much less well-known than that of Bletchley Park. Though that is, of course, a big part of my motive in doing the research for this episode. For me, there are two lessons of particular importance today from the Enigma story.
First, it shows that progress in cutting-edge technologies is rarely, if ever, the work of individual geniuses. This progress in intelligence or technology comes about over years of work, one layer adding to the last, in which sustained institutional effort is key. And more important, the story is a warning to all those in power today.
Last month, top officials in the US, including Defense Secretary Pete Hegseth, were revealed to have been discussing plans to bomb Yemen on their Signal apps. Indian intelligence personnel were earlier alleged to have used WhatsApp to plot top-secret assassinations against terrorists in the West. These stories demonstrate that while we use modern technology to communicate confidential information, we don’t fully understand its perils.
Lots of intelligence services across the world are always trying to peel the defenses of our secrets and will sometimes succeed. In their time, commanders thought the encryption technologies they were using were unbreakable. The team at Bletchley Park and their counterparts at the B-Department in German Naval Intelligence knew otherwise, for a fact.
The birth of Enigma
Less than 10 months before the end of the First World War, a German electrical engineer filed for a patent for a device he called Enigma, a typewriter-like gadget that encrypted text by passing electricity through a series of plugs and an alphabetical keyboard connected to a number of different rotators. The operator would type in the message to be encoded, the rotors would spin it through a constantly changing combination of alphabetic possibilities, and out would come the enciphered text, letter by letter. At the other end, the same machine reversed the process, allowing the encrypted text to be turned into plain language.
So no geniuses were needed at either end of the line. Arthur Scherbius, the Enigma’s inventor, was until then mainly known for his invention of an electrically heated pillow. The device, if which I am sure useful in the cold of Germany, did not exactly set the market on fire.
The German Naval Intelligence Service though saw the patent application and called Scherbius for a briefing, despite his lack of credentials or experience, which I guess speaks well of their professionalism. German Naval Intelligence, like all other intelligence services of the time, relied on distributing code books to their fleet. This method was cumbersome, since the physical distribution of these fat code books across the entire network was extremely difficult and vulnerable.
The British, the German intelligence also knew, had developed an upper hand in decrypting their traffic. A mechanical system like Enigma offered the prospect of ending the problem of distribution, as well as creating encipherments so strong it would be hard to defeat by any of the methods then known. To understand the significance of Scherbius’s machine, you need to understand the backdrop of the revolution radio frequency communication had brought about in military affairs.
Late in the 19th century, the Italian engineer Guglielmo Marconi had pioneered the wireless telegraph, which allowed for the transmission of Morse code messages, even when there were no wires, so out to sea or to remote battlefields. The problem was everyone, not just the intended recipient, could listen to a wireless broadcast and therefore, it was obviously vulnerable. First codes solved that problem and Enigma added by automating the creation of what are called polyalphabetic substitution ciphers.
With just one rotor in its mechanism, the Enigma could turn an alphabet into any one of 26 possible alphabets that was keyed in by the operator. With two rotors, this increased to 26 multiplied by 26 or 676 possible combinations. With three rotors, there were 17,576 combinations with 4,456,976.
And that’s not even counting the plug board. There is a great 3D simulation of this you can play around with online. Arthur Scherbius wasn’t the first person to come up with the idea of a mechanical encryption device, we know from the work of the historian Karl de Leeuw.
The first such device was actually developed by two Dutch naval officers, RPC Spengler and Theo Van Heng, in 1915. A prototype was built that very year by their colleague W.K. Moritz, a mechanical engineer who was serving on the Dutch fleet in the East Indies. For a variety of reasons, the Dutch Navy decided not to develop the device, but also stopped Spengler and Van Heng from applying for a commercial patent.
Likely, Scherbius heard of their device from his brother-in-law, Huybrecht Verhagen, a lawyer who worked at the firm which was involved in the aborted patent application by the Dutch naval engineers. The best ideas never stay secret, I guess. To be fair though, there were also a bunch of other people toying with similar ideas at around the same time, including Edward Hebern in the US and Arvid Damm in Sweden, who both developed similar successful machines.
The German naval intelligence officers who heard Scherbius’ machine were impressed, but their budget didn’t stretch to the 4,000 to 5,000 Reichmarks he was asking for each machine. Remember, the device would only have been useful to the German navy if they could spread it across their fleet and ground stations. The officers suggested that Scherbius instead try and sell his device to the foreign office, but the diplomats weren’t very interested.
In Jan 1918, Arthur Scherbius received a patent for his cipher machine design, which was later known as ENIGMA #TBT. https://t.co/CzIRqJEDtg pic.twitter.com/XZZecOzOcb
— NSA/CSS (@NSAGov) January 19, 2017
Germany was about to lose the First World War and no one wanted to waste money on a lost cause. In the end, Scherbius set up a company called Cipher Machine Joint Stock Company, which reached out to two of Germany’s neighbours as potential markets. That’s how Poland, which would be the first country Germany attacked in the Second World War, came to hear of this thing called Enigma. The one iron rule of secrets is, they always somehow get out.
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The codemakers & codebreakers
Late in 1923, as Germany began to sink billions of Reichmarks into its secret rearmament programme, it again needed a secure encryption machine for its military. Among the men in the room during the meeting with Scherbius was a young naval intelligence officer named Wilhelm Tranow.
Tranow soon rose to lead the team of codebreakers at the Beobachtung Dienst or the B-Department of the Oberkommando der Marine or OKM, the German naval elite. Tranow’s chance presence at the meeting was to have a key role in events to come. The amazing story of the institution, the B-Department he built, has been told by the brilliant historian Christian Jennings, about whose work I cannot say enough good things.
Even though the Nazi armed forces suspected that their communications had been intercepted, faith in the statistical invulnerability of Enigma remained strong, with disastrous consequences at key junctures in the war. The Germans knew, for example, that their campaign against Allied shipping in the Atlantic was ending up costing them an abnormal number of submarines.
They just could not believe that the hardened naval Enigma cipher, though, had been compromised. There is no record I have been able to find of what Tranow’s position in this debate was, but it is probable that his team at B-Department would have warned against overconfidence. The reason is simple.
Even as Enigma was being hacked, the B-Department had broken the Royal Navy’s own uncrackable codes. From his days as a lowly radio operator in the First World War, Tranow had learnt that all British maritime traffic sent back at least one message every day, reporting their name and location. The commercial ships sent this message to their companies and to the insurance giant Lloyds of London, the warships to the Royal Navy’s headquarters at London and Portsmouth.
Tranow’s B-Department codebreakers, who were initially a very small team, found figuring out commercial traffic was easy enough. Every day, radio operators on each of the commercial ships would encipher their messages using a codebook and transmit the output in Morse code. The B-Department knew each report would have the name of the ship, as well as the words report and position.
That gave them three vital clues into the code used by the merchant ships. Given that the fleet was over 3,200 ships strong in 1924, there was a strong statistical foundation for using these cribs as they are called by encryption experts. For deciphering the massive volume of traffic.
Figuring out the naval code though was a bit more complicated. Each word and number was represented by a five-figure number in the Royal Navy’s big fat government telegraph code. This code was of course changed periodically with new codebooks being issued throughout the system.
Like the civilian code though, the military code suffered from one built-in vulnerability. German agents across the world would know when a warship had left, giving B-Department information on its location, name and type. There were dozens of warships at various ports each day, which transmitted coded messages on their arrivals and departures.
So the cryptological attack needed patience more than cunning. Each time the codes changed, of course, the code breakers needed to start from zero again. The sheer logistical difficulty of changing codebooks across a massive fleet dispersed through the entire world, one were deterrent against frequent upheaval though, and a friend of B-Department.
From the outset, Tranow wanted to protect the German Navy from the vulnerabilities of the codebook system he had successfully cracked. Enigma seemed to offer a good solution. The machine’s encryption required physical distribution of the sets only once, after which operators simply had to adjust daily settings for the rotors and plug boards.
The probability of a single alphabet ever repeating itself as we discussed was infinitesimal, and the chances of an entire word appearing twice, all but impossible. Even modern computers, we know, would need massive processing resources to decrypt Enigma by the brute force method of trying all possibilities. Together with his counterpart at the Army Cipher Bureau, Wilhelm Fenner, Tranow ensured Enigma was purchased and began to disperse across the German military by 1924.
This was trickier than it might have seemed. See, the German military programme was beset by problems. The Treaty of Versailles, signed after Germany’s defeat in 1918, laid sharp restrictions on rearmament, including the purchase of certain kinds of intelligence equipment.
Funding for the entire rearmament process was generated by bonds issued by the government, clandestinely routed through the Berliner Bankverein Bank, or from sales of military equipment carried out by the armed forces themselves. Walter Lohmann, the naval officer in charge of the secret rearmament, routed the funds through a series of bizarre fronts, including a bacon company which sold pig meat to the United Kingdom, another company that claimed to be extracting fuel from potatoes, and a third purporting, believe it or not, to be trying to salvage sunken ships using a new method that used ice.
Lohmann’s downfall though was a film company called Phoebus, which he used to promote patriotic content.His patriotic films, though, ran up very unpatriotic losses and the story eventually leaked to the press. Tranow didn’t know it, but the embarrassment of the revelation to the press of the rearmament programme was in fact the least of his problems. In 1925, less than a year after Enigma began to be introduced into the German military, a German veteran named Hans-Thilo Schmidt, who had been left disabled by poison gas in the First World War, left the military.
He began a life of multiple failed business ventures, all of which left him in severe debt. A relative managed to get Thilo a job at the new cipher bureau under Fenner, where they had just begun assessing Enigma. French intelligence in Berlin soon received an offer from Thilo to sell the Enigma, which was accepted.
Thilo provided the French with the Enigma machine’s instruction manual, operating procedures and lists of key settings. Even with this information, however, French and British cryptoanalysts were unable to make sense of the Enigma’s traffic. Tranow was clearly vindicated.
This machine was unbreakable. Except, and there’s always an except, German naval and land forces formally began using Enigma together on the 15th of July 1928 after all its tests were completed. The Polish signals intelligence service, which watched the Germans most closely, noticed a change in the pattern of traffic immediately.
The new German cipher they observed appeared to be substituting random letters for both vowels and consonants. The Poles already had a good idea; this had something to do with Enigma, which they had been offered for sale earlier, and began working on it independently. They also received help by a freak of chance.
Late in 1927, the Warsaw Customs Office had received a parcel from Germany claiming to contain radio equipment. The sales representative of the German firm immediately arrived on the scene to demand the package be returned without a customs inspection, saying it had been inadvertently posted to Poland and needed to be sent back home. The Polish General Staff’s Cipher Bureau obliged him, but not before it conducted a very thorough inspection of the Enigma machine inside.
In December 1932, Polish Cipher Bureau mathematicians Henryk Zygalski, Jerzy Rozycki, and Marian Rejewski first solved the Enigma code. Their success enabled the British to read encrypted German messages during WWII, contributing to Allied success: https://t.co/BEo4WgXWlH pic.twitter.com/amFuhZ5X37
— National Cryptologic Foundation (@NCFcyber) December 2, 2017
The mathematician Rejewski’s great breakthrough was to realise that the Germans deliberately transmitted the day’s rotor and key settings twice at the beginning of each message to make sure the receiving operator made no mistake. This gave the Poles two sets of letters which repeated themselves in a predictable place in the message. This meant that after lengthy exercises in numeric permutations, they managed to read one Enigma message on the same day that it was sent.
Two sides of the game
Tranow, meanwhile, stepped up his efforts to penetrate British naval traffic. Tranow discovered that although the British surface ships, submarines and small gunboat boats were all using different code books, they were using the same enciphering tables for all of them. Regardless of how complex Naval Cipher 1 or its cryptological brother the Naval Code might be, this became immaterial if the Germans could read backwards into the codes from their encipherment tables.
This meant that in order to be able to crack the three different codes used by the Royal Navy, Tranow only had to crack one set of tables. In simple language, think of it like this. The Royal Navy’s safe of secrets had three different locks, but just one key.
This was poor design and execution and Tranow cashed in on it. By August 1939, running just on a skeleton staff, he estimated that B Department was reading half of British naval traffic. By later that year, the British Administrative Code, the Auxiliary Code and Naval Cipher 1 were being cracked more than half of the time.
The first successes came just days after the war began in 1939. B Department was able to provide the German Navy the precise location of a 4060 tonne British merchant steamer en route from Buenos Aires to Swansea. The submarines U-35 and U-31 closed in on the convoy at sunset, followed it all night and at dawn sent an Enigma-coded contact report with its heading, speed and the number of ships.
U-Boat headquarters ordered every submarine in the English Channel and Eastern Atlantic to attack. Royal Navy Communications Intelligence rapidly put in place a new cipher system called Naval Cipher Number 2. But Tranow and his team discovered it recycled many of the old vulnerabilities. For instance, a British submarine or ship could leak insight into Cipher Number 2 when it transmitted from a location where a German ship was also present because B Department could match the German ship’s location against the location of the British ship.
The first great signal intelligence driven battle, the Battle of the River Plate, showed what knowing the other side’s secrets could gain, but also what it couldn’t. B Department’s work helped sink the Doric Star. The women and men at Bletchley Park, meanwhile, forced the scuttling of the Graf Spee.
The outcome, though, wasn’t a triumph for either the Kriegsmarine, the German Navy, or the British. Captain Langsdorff shot himself in the head with his service Luger pistol on 19 December, fearing he had ended up losing one of Germany’s great capital ships unnecessarily. As the war dragged on, both sides became increasingly sophisticated in their communications intelligence practices.
The introduction of an additional rotor into the naval version of Enigma made Nazi maritime communications blind to the Allies for some time. Alan Turing’s great achievement was to build an automatic computing device called the Bomb, which enabled high-speed decryption using what we today call algorithms. The Americans joined in, developing their own bombs with 37 times the speed of the British original.
The intelligence generated at Bletchley Park, codenamed Ultra, provided Allied leaders with a granular knowledge of Nazi plans. The two sides thus fought each other in North Africa, with intelligence providing deep levels of insight into their rivals’ actions and plans. The Allies eventually won because of a range of factors, including much better resources, but also improbable elements.
For example, the toilets the British army had in North Africa created less illness because it had more experience than the Germans of digging in and operating in tropical hot climates. Luftwaffe signals intelligence personnel similarly had tremendous success breaking Royal Air Force communications ahead of the Battle of Britain in 1940. The Germans developed the means to monitor, intercept, decipher and take action on most of the Royal Air Force’s important operational codes.
In theory, they should have given the Luftwaffe a huge edge, but it didn’t mean they had better aircraft, better pilots or better strategy. Knowing what the British were going to do in advance wasn’t always practically helpful either. In the months between June and September 1940, cryptanalysis still took a lot of time.
The Germans did indeed monitor, intercept and take decisive action on the Royal Air Force codes. In practice, RAF code intercepted at 8 a.m. had to make its way to Potsdam and would end up being decrypted by 12.30 p.m.. That meant plenty of advance notice for air defence units to shoot up slow-moving bombers that might arrive only at midnight. In the case of RAF fighters scrambling to intercept German bombers though, it meant that the German bombers would already be in the process of being shot down while Air Force Intelligence chief Ferdinand Vogel’s men were still subtracting four-digit letter groups from keywords in their encipherment table.
The great chronicler of Bletchley Park, John Ferris, who has also written the official history of the UK’s super-secret GCHQ famously asserts
Allied power was so much greater that probably the Allies would have won without Ultra though at a much greater cost. Politicians after the war would demand assessments of how many divisions intelligence was actually worth. A not inconsequential issue, remember, because the Red Army, the Soviet Union, had crushed the Nazis without a significant cryptological edge.
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The Fallout
The movie version of Enigma focused heavily on the tragic fate of Alan Turing after the Second World War, who was persecuted for his homosexuality and eventually forced on to a barbaric chemical castration regime that led him on to suicide.
#OTD 110 years ago, Alan Turing was born.
Turning was an English mathematician, computer scientist and cryptanalyst.
He helped crack the Nazi Enigma code and is now considered the father of modern computer science.
📷: HW 25/3 & Wiki Commons#Pride #PrideMonth pic.twitter.com/QUTaMJBk0m
— The National Archives (@UkNatArchives) June 23, 2022
There was an ideological battle within the Nazi intelligence services too, with the deeply Catholic Fenner trying to keep Nazis out of his ranks. This was hard to accomplish though and the Nazi Party members increasingly took over key positions.
Luftwaffe intelligence in particular, the Air Force, drew large numbers of Nazis who departed the organizations run by Fenner and Tranner. Fenner would later tell Allied interrogators: ‘OKWG, Naval Intelligence, was engaged in a war against an as yet unknown number of ‘foreign’ foes whose weapons were their cryptographic systems. The ‘inner foe’ which caused far more vexation was Air Chief Hermann Göring’s agency. It is true I was still in a position to hire people who as a rule had not yet left the church and were not in the Nazi Party. But a certain letting down of what we may term ‘attitude’ was present.‘
There is evidence that some in Nazi communication intelligence tried to use their position to actively destroy the regime. Erich Felglebel, Germany’s senior most signals officer at the time of his arrest and privy to every technical secret of the Third Reich, including the work on V1 and V2 missiles, was part of the so-called Lucy spy ring.
The other members included several officers holding key positions in the intelligence services, including Major General Hans Oster, the chief of staff to Admiral Wilhelm Canaris, the head of the Abwehr, the Nazi military intelligence organisation.
Lively debate still rages on whether the Lucky Ring passed on information of the Nazi offensive at Kursk, where its military backbone was eventually broken. There are a string of competing theories, including that ULTRA intelligence was directly relayed to the Soviet Union by John Cairncross, the British intelligence double-agent.
The most important consequence of the discovery of the Lucy disclosure, though, was that Hitler—wisely—began distrusting Admiral Canaris and the Abwehr, fearing they were plotting his downfall. The result, though, was that the Nazi high command became blind to the world around it.
I really hope someone makes a movie on these dramatic events some day. The code-breaking in B-Department was not of as high an order as that involved in Enigma, but German cryptanalysts registered great successes with limited resources. More importantly, some of them tried to save millions of lives in what they understood, perhaps far earlier than others, to be an unwinnable war.
The lesson for everyone else should be pretty simple: Don’t use Signal to plan the bombing of Yemen because, as US defence secretary Pete Hegseth has discovered, you never know who might be listening. The RAW (Research and Analysis Wing) spies who are alleged to have plotted assassinations in the US over WhatsApp might have been a lot wiser to whisper things in each others’ ears. There have even been suggestions that the unregulated use of things like Apple watches by high Indian officials, or even internet-connected gadgets in their homes, create dangerous vulnerabilities.
I’m reasonably certain no nation state in its right mind would waste its time and resources to intercept my e-mail or chat—and if it did, it would soon learn there’s not a lot waiting to be discovered there. There’s a world of people, though, whose words can win and lose wars. And the Enigma story reminds us that the stakes are incredibly high.
(Edited by Tony Rai)
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