(De)Ciphering the Holocaust

Bletchley Park, German Police Intercepts, and the Final Solution, 1941-42

Feb 15, 2024

At first, the codebreakers at Bletchley Park, Britain’s cryptanalysis center, couldn’t understand what the numbers meant, and then when they did they seemed scarcely believable. Within weeks of the Germans’ invading the Soviet Union on June 22, 1941—more specifically, from July 18 until August 31—Bletchley Park had intercepted some fifteen radio transmissions referring to mass shootings of “plunderers,” “commissars,” and “partisans,” often prefixed by “Jew” or “Jewish,” and which ranged from 61 and 4,200 at a time.

On August 7, SS-Gruppenführer and General of Police Erich von dem Bach-Zelewski, one of Reichsführer-SS Himmler’s more gruesome subordinates (and a man who somehow escaped the noose after the War), had gone so far as to boast in a signal home that “the figure of executions in my area now exceeds the 30,000 mark.” (Bach-Zelewski’s “area” was Russia-Center; the other two were Russia-North and Russia-South. The intercepted transmissions until late August came only from Russia-Center, probably owing to gaps in British coverage.)

There seemed to be neither rhyme nor reason to the figures except that the average number of daily homicides was trending upwards. The British had no idea as to why at the time, but it was owed to a broadening of the operational remit as the invasion went on. Initially, there had been a general order to round up Jews and Bolsheviks, but in early July it was changed to read that military-age Jewish males were to be shot, then at the end of that month a more specific directive said that all Jewish males were to be killed, and finally in mid-August it was extended to include Jewish women and children.

It took a little while for the directive to reach every unit, but soon afterwards the effects were reflected in the intercepted transmissions. For instance, Police Battalion 314 reported on August 24 that 294 Jews had been shot, and the next day Police Regiment South’s three battalions collectively recorded 1,342, and then on August 31 Police Battalion 320 alone reported that 3,200 had been killed.1

All this was strange enough to the men and women sitting in the rudimentary wooden huts pocking the Bletchley grounds. Stranger still was that these Aktions were, as evidenced by Bach-Zelewski’s involvement and the origin of the transmissions, being carried out by what had once been the German municipal and regional police—now unified into a paramilitarized Ordnungspolizei (ORPO), “Order Police.”

Bletchley Park was confused as to their motives. The cops weren’t arresting people, they were killing them. But why? The best guess, ran an analyst’s note accompanying Bach-Zelewski’s August 7 signal, was “that the word has gone out that a definite decrease in the total population of Russia would be welcome in high quarters and that the leaders of the three sectors [North, South, Central] stand somewhat in competition with each other as to their ‘scores’.”

That civilized people could not quite wrap their heads around the scale of what was happening meant that the British downplayed the Jewish specificity of the murders. “The execution of ‘Jews’ is so recurrent a feature of these reports,” noted one official, that he doubted whether the victims were in fact all Jews.

As the Germans were lazily categorizing executed partisans and looters as “Jews,” the police were clearly organizing only “a policy of savage intimidation” to keep order behind the lines. The reason why the Jewish category was so much larger than the others was owed to the German habit of trying to please their superiors.

Unpleasant, sure, but he could find no evidence that any “ultimate extinction” of the Jews was intended.

The Police Ciphers

But perhaps strangest of all was that the messages were sent in the cryptological equivalent of a kid’s Secret Decoder Ring. To people accustomed to breaking hard nuts like Enigma, with its hundreds of billions of possible combinations and its technical complexity, solving it was as challenging as doing an easy-level Sudoku during the morning commute. That someone of Bach-Zelewski’s rank was using it was astonishing.

This was a cipher so routine that the British had been reading German police communications since even before the War. Then, they had been interested in assessing the level of dissent within Germany, and the police obliged their interest by relying on a Double Transposition system (here’s a simple guide), which was done by hand using code tables. For the local 5-0, it was tedious to scramble and rescramble the letters of a message, but it worked well enough—at least in peacetime. During wartime, however, Bletchley Park used it to train newbies.

What no one could work out was why, when Enigma was available and widely used by the armed forces, German cops were still sending these mysterious messages in low-to-medium-grade Double Transposition.

The answer was that they didn’t know how to. ORPOs were hardly the intellectual cream of the security services and they hadn’t been trained to use the advanced Enigma machines. Those took months to learn, and longer still to become good at.

Luftwaffe technique, for instance, was notoriously sloppy—Bletchley Park blew most of their Enigma keys within weeks—which was why Admiral Dönitz of U-Boat Command, which had the best operators and the highest security, always kept his precious Naval Enigma separate from Göring’s Air Force idiots. It’s revealing that the only people who approached the Reichsmarine’s virtuosity were the Gestapo, whose craftsmanship was so impeccable that Bletchley Park, despite its best efforts for six years, never broke TGD, its private Enigma key.

ORPO wasn’t anywhere even near Luftwaffe standards, let alone the Gestapo’s. True, there was an ORPO signals school in Berlin a few had attended, but its graduates tended to be older men who had learned their skills in the Great War—and preferred to stick to the equipment and techniques with which they were already familiar. A hand-ciphered Double Transposition, in other words.

Neither could the police regularly use landlines or air couriers to communicate sensitive information to headquarters. Light airplanes like the Fieseler Storch were in short supply during the invasion and in any case couldn’t be used over such long distances. And as for telephone lines, there were few in Poland, Ukraine, and the Baltics to begin with, and those that did exist were reserved for the military. Even the Higher SS- and Police Leaders (HSSPFs), who reported to Himmler himself, had to specify that their call was Exceptional or Urgent before they were put on a waiting list behind the Wehrmacht.

Which left only the radio.

The Crime Without A Name

The reports intercepted by Bletchley Park were passed on to MI 14, the military-intelligence branch of the War Office that specialized in German affairs. From there, it’s hard to see where they went or who saw them. It’s certain that Prime Minister Churchill was informed about some of the atrocities because on August 24, 1941, as the killing accelerated, he gave a radio broadcast stating that “whole districts are being exterminated. Scores of thousands—literally scores of thousands—of executions in cold blood are being perpetrated by the German police-troops upon the Russian patriots who defend their native soil.”

Churchill, following the lead set by his intelligence heads, did not highlight the fact that the “crime without a name,” as he put it, was targeting Jews. Instead, partly as a sop to Stalin, he played up the “Russian patriots” aspect.

This mirrored, or perhaps reflected, Soviet propaganda. Moscow had always insisted on bundling Jewish murders into a general category of “German-Fascist invaders” murdering “peaceful Soviet citizens” (including, for instance, Ukrainians, Tajiks, Georgians, Armenians, etc.) and brave Russian soldiers. Many Soviet citizens and soldiers of all nationalities were murdered, of course, but Stalin had an interest in stressing the “Soviet” aspect both for patriotic reasons but also to cover up his own extermination of 20,000 Polish officers in 1940 at Katyn by blaming their deaths on a generalized Fascist threat to Communism.

Churchill was not complicit in any of this, obviously, and he was as hopelessly confused as anyone else. From the intercepts, it certainly looked as if the ORPOs had turned their attention away from Jews and were focusing on killing Russian soldiers. On August 30, for instance, Police Regiment Center shot 244 Red Army prisoners and it was known that Bach-Zelewski’s men were being drafted to assist the Army hunt down partisans. Meanwhile, patchy coverage meant that no transmissions concerning Jewish liquidations were intercepted, despite Police Battalion 322, among others, radioing headquarters on September 1 that it had executed “1171 Jews and 8 communists” near Minsk.

In that light, Churchill’s conflation of “Russian patriots,” prisoners and partisans, and Jewish civilians is understandable. In his speech, though, he did get the specific “police-troops” part right—too right.

The British always kept even the wispiest hint that they could read much of the Enigma traffic out of any of their transmissions, public or private, in case German ears were pricked. This caution would save their bacon in 1942, when the B-Dienst (German Naval Intelligence) brilliantly penetrated Naval Cypher No. 3, the code used by the Allied navies to oversee Atlantic convoy operations and ward off U-boat attacks.

Churchill was always very good about maintaining this level of security, despite every temptation, but German police ciphers were not Enigma and so not as closely supervised.

Thus it was Churchill’s mentioning “police-troops” that startled Karl Deluege, Generaloberst of the ORPO, into improving security. On September 13, he informed his units that “the danger of decipherment by the enemy of wireless messages is great"—this particular wireless message was, ironically, deciphered by Bletchley Park—and ordering that henceforth any geheime Reichssache (Top Secret) data on executions was to be sent by courier.

The Playfair

As mentioned earlier, couriers were few and far between at the time, so this was a custom observed mostly in the breach. So, stuck with radio, the ORPO belatedly switched from Double Transposition to a system known as Double Playfair.

The original Playfair had been invented by the British in the 19th century and all of its tricks were well known—not least to the Germans, who had broken it in 1915. Double Playfair—you can read about it here—was a tougher variant, but the ORPOs made unwitting errors that allowed British cryptanalysts a way to reconstruct the key.

The German policeman’s precise and respectful mind insisted on spelling out, for instance, easily guessable ranks like SS-Obersturmbannführer (lieutenant-colonel, essentially) or pedantically repeated giveaways like Kriegsgefangene (prisoners-of-war). Using that many characters over and over again in known words was cryptographical Kryptonite as it gave away cribs.

A crib was a hack into a message’s key that was used to begin the process of converting ciphertext into plaintext. You didn’t need to know all 26 ciphered letters of the alphabet before you begin decrypting a message. At Bletchley Park (and later OP-20-G, the U.S. Navy’s first-rate outfit which everyone ignores owing to Imitation Game-induced Bletchley Parkitis and Alan Turingism, but enough about that), which used bombes (electro-mechanical machines that filtered out impossible combinations), you could at least start making a stab at it when you had perhaps nine letters—and that was for one of the hardest keys, known as Triton to U-Boat Command and Shark to Bletchley. For breaking something like Double Playfair, being handed Obersturmbannführer or Kriegsgefangene made for an absurdly easy crib.

It was exactly this kind of sloppiness, I should mention, that drove U-Boat Command nuts. In Naval Enigma, orders from Dönitz never referred to his rank in full, Befehlshaber der Unterseeboote, but only to a variant such as BDUUU or BEFHBR.UUUBTE, and it was changed for every signal to avoid repetitions.

Breaking Playfair, it would turn out, was less useful than had been expected. By October/November, following Deluege’s instructions, ORPO units ceased to report Jewish massacres by radio at all.

That was because that winter mass ORPO shootings outside towns or in local ravines were being replaced by liquidations at SS-controlled death camps like Treblinka, Majdanek, Sobibór, and Bełżec, where trainloads of arriving Jews would be gassed within an hour.

The Next Phase

From their embassies in neutral countries, the British had for some time been receiving reports of large-scale deportations from western Europe and the Reich, but where they were being sent—aside from “The East”—remained mysterious. There were some hints that Jews were being conscripted and exported as slave labor to Ukraine, Poland, and Galicia, but details were sparse. A couple of intercepted police signals referring to transports deporting some 2,000 Jews from Bremen and Berlin provided some additional evidence that something was happening, but what was uncertain.

What was happening was Operation Reinhard, in which the tempo of extermination quickened as much as its scale ballooned. In March 1942, around 80 percent of those who would be killed in the Holocaust were still alive; a year later, 80 percent of its victims would be dead.

The British had much less information about the death camps than about the shootings. Reinhard Heydrich, head of the Reich Security Main Office and Himmler’s choice to oversee the Final Solution, unfailingly used high-grade Enigma to communicate with his underlings. In August 1941, he had been cautious enough to order Einsatzgruppen commanders to burn any orders from him and if it was impossible to transmit by Enigma then they were to return reports in writing.

But they knew a little more about the forced-labor sections of the camps thanks to an administrative Enigma used by the SS called Orange. It had been broken back in December 1940, and Bletchley Park had read it off and on since. Usually, it wasn’t very interesting, but in the spring of 1942 Bletchley Park began intercepting snippets of information from a place named Auschwitz.

Much of it was run-of-the-mill stuff, sent in Orange because, unlike reports of shootings, it was not classified as Top Secret. For instance, no decrypt during the entire War ever mentioned gassings—which certainly was Top Secret—but an order in November 1942 for 600 gas masks for camp guards was sent in Orange because it was regarded as a standard requisition by the concerned staff at Auschwitz. The same applied to a routine instruction “to hand over useless Jewish clothing to the clothing works at Lublin.” As for Bletchley Park, they had no idea what the masks were for or why there was so much “useless Jewish clothing.'“

As Auschwitz’s labor requirements were counted as only moderately secret they were reported by radio in Orange. Almost every day Auschwitz sent a report listing the camp population and a numbered breakdown of prisoner categories (Jews, Poles, Gypsies, Germans, Russians, etc.). In these reports, deaths were recorded as “natural” when they were actually the result of shootings, beatings, torture, starvation, and disease.

Many years later, the Bletchley Park cryptanalyst and future historian Peter Calvocoressi revealed that these “random” numbers were extremely useful for breaking the daily Orange (and other) Enigma settings, making “these sad, grisly statistics of human suffering and indignity [play] a part which the piteous victims never dreamed of.”

Such utility aside, what the figures showed was that between January and March 1942, there were only several hundred Jews at Auschwitz (from 191 in January to 380 three months later). But from April, there were thousands (these were mostly Slovakian deportees), and on July 10, nearly 6,000. On July 17 Himmler ordered that “selections” were to start taking place on the ramps at Auschwitz, which partly explains why in August, when there were 12,000 Jews there the mortality rate exploded, with no fewer than 6,889 men and 1,525 women dying. This increase was attributed by the British entirely to an outbreak of typhus.

Still, analysts noticed a strange idiosyncrasy: In August, what the Germans had begun to refer to as “departures” (accurately interpreted by the British to mean deaths) was being “balance[d]” against arrivals—5,325 to 4,989 over nineteen days— almost as if trains were being systematically scheduled to deliver new Jews in sync with the “departures” of old ones dying, apparently, of typhus.

As of February 1943, however, the stream of prisoner reports sent by radio stopped and Auschwitz went dark. But in truth Auschwitz had always been dark. All that had ever been known was inmate numbers, not liquidation numbers: The vast majority of Jews arriving at Auschwitz (around 865,000) were never registered and were gassed immediately, not sent to Auschwitz’s labor component for processing.

The British had never seen those figures. Yet there were isolated glimpses into what was happening—just very rarely in ciphered form.

From 1942, they received intelligence from sources other than Enigma or police decrypts. Some prisoners escaped and told of their experiences; the Polish Government-in-Exile told of gassing experiments on Soviet POWs and Polish political prisoners that had taken place in September 1941; the Polish Underground reported that there were crematoria in operation; and train signals had been intercepted containing timetables of Jewish transports.

The British, then, were sure that mass murders were occurring, but the most horrendous reports of mass gassings and the like were written off, as had become customary, as atrocity stories cooked up by Poles and Jews.

The Typo

All of which meant that even when there was firm evidence of a genocide, it was laid aside as claiming the inconceivable and the impossible. In January 1943, an intercepted signal sent from the SS and Police Leader in Lublin to the SD commander in Krakow and Eichmann himself in Berlin carelessly let leak the fact that 1,274,166 Jews had been killed in Treblinka, Majdanek, Sobibór, and Bełżec over the course of 1942.

To those who read it, the total was clearly a typo: No one could kill that many people so quickly—that’s an average of 106,000 people per month, a figure beyond comprehension . . . unless one was able to compass the monumental scale of modern industrialized slaughter and the depth of human depravity in a barbaric century. Of this, the genial crossword experts and eccentric Oxbridge dons of Bletchley Park were, sadly, incapable.

And in fact, there actually was a typo in the message—the number for Treblinka was given as “71355” instead of 713,555—lending credence to the view that because the signal was erroneous nothing should be done.

Conclusion

It wasn’t until 1996 that the Enigma and police decrypts were publicly released and even then there were many questions as to who had seen them, what actions had been taken, and the extent of their impact.

One lesson that can be drawn here is that intelligence is never an open-and-shut case—and rarely are there smoking guns and bloody fingerprints left conveniently behind. (And even when one is, as mentioned just above, it may not be seen for what it is.)

In this case, all there was were isolated snippets and facets of the truth that were contradictory, inconclusive, incomplete, or ambiguous. They could only have been pieced together to form a relatively coherent picture had there been an ability, the imagination, or even the willingness, to comprehend the magnitude and black ambition of the Final Solution.