Another ground for suspicion of Lucy is that not one of Roessler’s alleged sources surfaced after the war ended. If they were really members of OKW or OKH, both defined by the victors as criminal organisations, their careers, incomes and prospects had been terminated by the Wehrmacht’s defeat and disbandment, and they faced the prospect of at least a denazification hearing or possibly even a trial as war criminals. Their reception by Moscow would have been problematical; on returning there both Rado and Leonid Trepper, the Red Orchestra’s ‘Big Chief’, were charged with having been German-controlled double agents, ‘rewarded’ with 10-year jail sentences, rehabilitated and freed only after Stalin’s death. However, American or British Intelligence services would surely have welcomed Lucy’s ‘sources’, and even have sought to recruit them as double-agents in the rapidly evolving Cold War, and that would have considerably improved their lives in devastated post-war Germany. Could it be that if Roessler had provided names, then the British, Americans or Soviets would have tried to contact them directly, and would then have found that they did not exist?
The contention that Lucy was a German-controlled double agent is inconsistent with the fact that it was German pressure that obliged the Swiss in October 1943 to locate Rado’s transmitters and shut his ring down. However, there are at least three possible explanations for that. First, that it was a genuine espionage ring, to which the Sicherheitsdienst or Gestapo failed to apply the preferred counter-espionage solution of turning at least some of its members, as they did with the Red Orchestra, and as the British did with all German agents sent to the UK, and the Soviets did with agents sent in to support Max. Secondly, it may have been felt to have outlived its utility as disinformation, and that the Soviets were no longer reacting as expected. Thirdly, it could even be, as is not uncommon in espionage, that the right hand, Gestapo or Sicherheitsdienst, did not know what the left hand, the Abwehr, was doing. That no arrests in OKW or OKH accompanied the shutdown suggests that if Roessler had sources there, they were extraordinarily good at covering their tracks, or were indeed participants in a ‘disinforming’ operation shut down because it had outlived its usefulness. Or it could be that the information was, as Sudoplatov claimed, ‘planted’ by the British, or came from Swiss Intelligence, and that the Swiss complied with the German demand because by October 1943 it was clear that Germany’s defeat, though not imminent, was inevitable. The ring was therefore no longer needed, and continuing risked exposing their own role, prompting a German blockade or even invasion. Evidence to establish the truth is not in the public domain, and probably never will be.
Advance Ultra information from Bletchley may have been among the factors influencing Stalin’s decision of 12 April, but was not definite enough to have been the only factor. Its main utility was that later messages provided useful information about German preparations to the Soviet General Staff planners of the defensive battle. The British official history noted the first signs of German preparations in the third week of March 1943, from decrypted Luftwaffe messages ‘about the movement of panzer divisions on the central sector of the eastern front, and are organisation of GAF [German Air Force] commands which brought Fliegerkorps VIII back to the Kharkov area for close support operations’. Then on 13 April another Luftwaffe message first used the codename ‘Zitadelle’ (‘Citadel’), and on the 19th another disclosed that Luftflotte (Air Fleet) IV ‘was sending forces allocated to Zitadelle to GAF Command East’. If the messages from the third week of March were passed quickly to Moscow, officially in paraphrased form or unofficially by one of the ‘resident’s’ agents, they could certainly have been taken into account in the Soviet decision-making, and may help account for what Stalin told Mikoyan on 27 March, but those of 13 and 19 April cannot have influenced the principal decision about how to fight the battle, because Stalin had already taken that on the 12th, when he endorsed the proposal Zhukov had made on the 8th.
The same reservation applies to the most comprehensive of the early indicators deciphered by Bletchley, a message from Field-Marshal von Weichs, commanding Army Group B, transmitted some time after 15 April and decrypted on the 25th. The gist of it may have been passed on officially to the Soviets, but according to two post-Soviet publications the State Defence Committee received a translation of the actual text from the NKVD ‘resident’ in London on 7 May; one of the accounts says it had been passed to him by Philby, who had received it from Cairncross. A post-Soviet account of Soviet Intelligence operations during 1941–45 devoted an entire chapter to Cairncross. It said that,
in his new job at Bletchley Cairncross received access to a whole range of deciphered German documents, which were immediately passed to Moscow. Philby also had access to a range of such documents – they were sent to him by the Chief of Intelligence. Blunt also sometimes managed to acquire some materials. But Cairncross had these documents in his own safe, and could use them as they arrived, i.e. without great delay. He passed on very important information about the offensive the Germans were preparing on the Kursk salient, indicated approximate dates for the offensive, the technical parameters of the new German ‘Tiger’ tank, and other information. By his self-sacrificing work he made a serious contribution to our victory at Kursk and on other fronts.
The same post-Soviet account credited the NKVD ‘resident’ in London with 14 agents altogether; since MI5’s post-war investigations did not, at least publicly, identify anything like that many, there may have been more than one still unidentified ‘mole’ passing on information. Certainly the Weichs message and anything else the ‘resident’ obtained about ‘Citadel’ would be very helpful to the General Staff planners, but Stalin had taken the crucial decision two weeks before Weichs’ message was deciphered, and four weeks before the State Defence Committee received its translated text. As for technical details of Tiger tanks, the Soviets did not need them; as noted below, they captured several between November 1942 and April 1943, and put them through comprehensive tests in April.
Although Ultra information from Bletchley cannot have been the sole or principal source of Zhukov’s and Stalin’s confidence as early as April about German intentions, information, particularly from Cairncross, about the methods employed in deciphering may nevertheless have played a role in the Soviet decision-making. When the Germans invaded the Soviet Union, the British decided not to share the Ultra secret, believing Soviet security to be German-penetrated, and expecting the Red Army would be speedily defeated. After both assumptions proved wrong, they took to passing on important information from Ultra, paraphrased and without disclosing the source, beyond dropping vague hints about an agent in the German High Command. The Soviets pretended to believe them, but obviously knew exactly what the source was, on information from Cairncross, Philby, Blunt and maybe others among the alleged 14 agents. Perhaps even more important than any information they passed on would be the messages’ evidence that many Enigma-based systems (and, as with the Weichs message, even the more complex ‘Tunny’) had been broken, and that large numbers of messages were being deciphered daily, often within only a few hours of transmission, to the great benefit of the Anglo-American war effort. Even before the war the Soviet Union had had a large interception and decrypting organisation (Sudoplatov mentioned that they were deciphering messages to or from several foreign embassies, including those of Japan, Italy, Turkey and Bulgaria), and the discovery from their British agents that the German cipher systems were breakable would justify a large commitment of intellectual and material resources.
In that connection the account mentioned above goes on to say:
Along with material of a military-operational character, Cairncross passed on data about the machine-cipher Tunny, which was used by the British to decipher German radio messages. On the basis of these data an analogous example of this machine was designed…In the operational file there is a task set by the Centre to the London residency. In particular it is stated that the Germans have made some changes in the machine’s design, and that therefore additional data are required, data that maybe are known to the British and accessible by Cairncross. The data were received from the source and sent on to Moscow. There is no information in the file about the further fate of this deciphering machine.
Tunny was Bletchley’s codename for the German SZ40 (Schluesselzusatz, ‘key-adder’) cipher machine and its derivatives, several versions of SZ42, used for communication at the highest military levels, such as between OKW/OKH and the headquarters of army groups, and including the message from Weichs, mentioned above. It was first observed in use in mid-1941, and by January 1942 Bletchley ‘understood its design and method of operation’. It was far more sophisticated than Enigma, so decryption was ‘normally too laborious to be undertaken by hand, and the first stage of mechanisation was the provision of a decyphering machine, delivered early in June 1942’. As to the unknown ‘further fate’ of the machine, if the reference is to the British machine, it is quite wrong. The first machine-deciphering successes were achieved in early May 1943 by a machine codenamed ‘Robinson’, replaced in February 1944 by Colossus 1, the first programmable computer. The reference must be to an attempted Russian counterpart to ‘Robinson’, otherwise why would Moscow ask its London ‘resident’ for data that could be obtained only from someone actually working at Bletchley? The most likely reason why there is nothing further on file is simply that they could not make the Soviet machine work, but that they even tried suggests a high level of cryptanalytical effort.
Bletchley could not acquire much Enigma traffic from German army units on the Eastern Front. Every division commander had an Enigma machine and radio transmitter in his command vehicle, but except when actually on the move most communication after December 1941 was via landlines, making use of radio too sporadic and the amount of traffic picked up by UK-operated intercept stations too small to decrypt on a regular basis. The best source of information about the Eastern Front remained the Luftwaffe general (‘Red’) cipher. ‘Fish’ messages, though taking longer to decrypt, were also valuable because the information they contained was more high-level, and consequently took longer to become outdated.
The Soviet situation was different. Landlines could be, and frequently were, tapped. During the Battle of Moscow for example, a German unit reported killing a Soviet officer who was doing so. General S.P. Ivanov, Vatutin’s Chief of Staff at Stalingrad, mentioned in his memoirs both receipt of a decrypted message that had been transmitted less than 36 hours previously, and a successful tapping operation against the Romanian 3rd Army. Line-tapping was also among the tasks set for partisans operating behind the German lines.
Radio interception of enemy traffic was frequently mentioned in Front commanders’ reports from late 1942 onwards, though in most cases the references were to voice communication, especially between German aircraft and ground controllers. It is also relevant that Bletchley found Luftwaffe cipher systems easier to break than those of the army or navy. German army operations depended heavily on air support, and in early 1943 about 60 per cent of the Luftwaffe was on the Eastern Front. Luftwaffe liaison officers (Fliegerverbindungsoffizieren, or ‘Flyvos’), each with an Enigma machine, were regularly attached to army units, and their messages frequently provided valuable clues about army operations.
The many secrets unveiled in the post-Soviet era have as yet included very little about the role of cryptanalysis in the Soviet–German war. That high-level Soviet communications were very secure is clear from the experience of Bletchley’s German counterpart, the B-Dienst; it found Soviet low-level tactical military ciphers easy to break, but had no success above that level. Front or higher-level Soviet commanders used Baudot machines and landlines, so messages could not be regularly intercepted, and Soviet diplomatic traffic used codebooks plus one-time pads of randomly generated figures; if these are properly used, messages can be deciphered only by those holding both book and pads. It is therefore reasonable to assume that Soviet expertise in codes and ciphers was of a high standard; the simplicity of tactical ciphers was mainly because low-level transmission resources were often primitive, originators and receivers of messages were not highly trained cryptographers, and any action proposed or requested in tactical-level messages would usually be taken before any third party could decipher or act on them.
In addition to a massive intellectual and technological effort, the British mounted substantial operations (e.g. a commando raid on the Lofoten Islands, seizure of German weather ships in the North Atlantic, recovery of machines and documents from captured U-boats) in order to secure single Enigma machines and associated documentation such as key tables. The surrender of the German 6th Army and part of the 4th Panzer Army at the end of January must have provided Soviet cryptanalysts with a number of Enigma machines and associated documentation far beyond what any British or American operation acquired. Each of the 20 division and 5 corps commanders had one such machine; the 6th Army headquarters had at least one, and may have had a ‘Fish’ machine as well. Some Flyvos probably escaped on returning supply flights, but by 17 January the Soviets had taken six of the seven local airfields, and made the seventh unusable by artillery fire and air attacks, so there were no landings or take-offs in the remaining days before the final surrender, and most Flyvos must still have been in the city. Even if only five were still there, that brings the total of Enigma machines in Stalingrad to 30. The troops were freezing and starving, ammunition, explosives and fuel were almost all gone, the ground was frozen too hard and the troops too weak to destroy or bury the machines. They could at most take a rifle-butt to them, and in some cases not even that – one last message ended with ‘the Russians are breaking in…’. It is also unlikely that key tables, operational documents and manuals were all destroyed, and it is entirely speculative, but not unreasonable to postulate that the haul of machines and documents at Stalingrad facilitated a ‘last heave’ by an already existing programme that had made progress, but not yet resolved all the problems.
This treasure-trove became available only in the first week of February, too late for much exploitation before Manstein’s offensive at Kharkov, but during March it may have become possible to decipher some Enigma traffic, including messages between divisions and armies concerning preparations for ‘Citadel’. Divisions on the move would sometimes have to resort to radio transmission – the order to observe radio silence applied to operator chatter and plain text messages, but not to enciphered traffic, because the Germans did not learn until 27 years after the war that the British had broken their ciphers. Interception of such transmissions could have been among the factors giving Zhukov the confidence about German intentions that prompted his message to Stalin on 8 April. Information from Front Intelligence and partisan observations of eastbound rail traffic would certainly also have been involved, but the most significant preliminary move, the German IX Army’s withdrawal from the Rzhev-Vyazma salient, took place by stages between 1 and 14 March. As noted above, this released up to 22 divisions to IX Army reserve, and hence to eventual availability for ‘Citadel’. However, with movement impeded by the spring thaw, and the need to employ several of these divisions to stop the attempted offensive by the Bryansk, Central and Voronezh Fronts, major redeployment into starting positions for ‘Citadel’ could not have been far enough advanced by the first week of April to account by itself for the confident tone of Zhukov’s message to Stalin.
Bletchley’s analytical effort naturally depended mainly on mathematicians, and although the relevance of chess-players is less obvious, work there did attract a number of them, including several of high international ranking. Russia was not short of mathematicians and chess champions, and given what it learned about Ultra from Cairncross and others, Soviet Intelligence must have devoted a large effort to Enigma-breaking. Intelligence failures up to mid-February 1943 suggest no or very limited success until then, but the least implausible explanation for the very marked improvement thereafter is successful exploitation of materials captured at Stalingrad.
No Russian account gives any details about where Stavka received the information that led it three times (on 2 and 20 May, and 2 July) to notify the two Front commanders in the salient that the German offensive would begin within a few days. In fact Hitler first set the date as 3 May, but changed his mind on 29 April, because he considered the numbers of the new tanks, assault and anti-tank self-propelled guns so far available to the attacking divisions insufficient. He then set a new date of 12 June, but ‘events in the Mediterranean’ (specifically the surrender of all Axis forces in North Africa on 12 May) forced another postponement, and even raised the possibility of abandonment. However, on 21 June he fixed the launching date for ‘Citadel’ as 3 July, then on the 25th changed it to 5 July. Stavka’s warning to the commanders on 2 May fits with Hitler’s original starting date of 3 May, and it is just possible that it was based on intercepted traffic. Hitler’s original order specified that Army Groups Centre and South must be able to launch ‘Citadel’ on five days’ notice. A launch on 3 May would therefore have to be ordered by, at the latest, 29 April, the date on which Hitler cancelled it. There is no information in the public domain to indicate whether any orders had been issued before the cancellation. The 20 May warning was simply wrong, but no Soviet or post-Soviet source has said on what it was based. The third warning, on 2 July, was absolutely correct, and its timing is interesting. It was only on 1 July that Hitler assembled at his Rastenburg headquarters the marshals and generals who would lead ‘Citadel’, Manstein, Kluge, Model, Hoth, Kempf and the commanders of the two air fleets, von Greim and Dessloch, and ordered them to start it on the 5th. The time of day of this meeting is not known, but since Hitler, like Churchill and Stalin, habitually worked into the small hours and then slept until at least mid-morning, it was unlikely to have taken place before 10 a.m. German summer time, which was 11 a.m. Moscow time. Stalin’s message warning the Front commanders that ‘Citadel’ was likely to be launched ‘during the period 3–6 July’ was transmitted at 2.10 a.m. Moscow time on the 2nd. That is 1.10 a.m. German time, at most only 15 hours after the meeting at which Hitler gave his generals their final orders.
This rapidity suggests two possibilities. One is that by then some Enigma traffic was being read. After the meeting, and before leaving headquarters, Manstein, Kluge, Model and Hoth, and probably also both air fleet commanders, would necessarily send orders to their own Chiefs of Staff to start alerting subordinate formations to prepare for battle, though without telling them the starting date. Messages from OKH to the headquarters of Army Groups Centre and South would probably use the more complex Fish machine cipher, and be sent by landline, but those from army headquarters to divisions or corps and to Luftwaffe units would be enciphered on Enigma machines, and some of them would be transmitted by radio, therefore vulnerable to interception.
The other, simpler, possibility is that the Soviets could intercept but not decipher Enigma messages, but concluded from traffic analysis that action was imminent because of the sudden large increase in traffic caused by the messages that Army Groups Centre and South and the army and air force HQs under them had to send, to alert their subordinate formations. Either possibility fits the speed of Stavka’s warning to the Fronts better than the idea of messages going from a source in OKW or OKH to Roessler in Switzerland, then through one of his intermediaries, Schneider or Duebendorfer, to Rado, who would then have to encipher it and contact one of his operators to have it transmitted to Moscow. Messages that Rado cited in his memoirs invariably took two or more days to be delivered.
Whatever the means that secured them, the improvements in Soviet Intelligence enabled Stavka’s planning for the summer to proceed more or less in parallel with the German. However, the planners were soon confronted by the disconcerting discovery that the new German Tiger I heavy tank was far superior to their prized KVs and T-34s because of its thicker armour, superior binocular sights and much longer-range and greater-calibre 88mm gun. Tempting fate, the Germans in late 1942 had sent a small pre-production batch of the new Henschel Tiger Is to the Leningrad front, where one became bogged in marshland and was captured. However, the Red Army’s tank and artillery specialists were preoccupied at that time with the situation around Stalingrad, so the encounter then attracted little attention. In December a battalion of Tigers was included in Hoth’s force that attempted to lift the siege of Stalin grad, then in early April 1943 some damaged Tigers were captured near Belgorod.
Tests conducted on 25–30 April, using various calibre anti-tank, field, tank and anti-aircraft guns, showed that armour-piercing shells from the 76.2mm F-34 gun then standard on the T-34-76 and KV-1 could not pierce even the side armour of a Tiger at more than 200 metres, while the Tiger’s 88mm shells could penetrate 110mm of armour at up to 2 kilo metres (1.25 miles). The thickest frontal armour on Soviet tanks was 100mm on the KV1 and 45–60mm on the T-34-76; therefore all would be vulnerable for the time it took them to get within killing distance of a Tiger. Even if they could cover the 1.8 kilometres (about 1.1 miles) at full speed, it would take them over two minutes; a Tiger could fire several rounds in that time, with a good prospect that one of them would score a direct hit.
Nor was the Tiger the only threat to Soviet tanks. The Ferdinand assault gun had an even more powerful 88mm gun than the Tiger, and thicker frontal armour, while the new medium Mark V Panther tank and newer examples of the older Mark IV mounted a long-barrelled 75mm gun, shells from which could penetrate the frontal armour of a KV at 1 kilometre (0.62 miles) and of a T-34 at 1.5 kilometres (0.93 miles). In addition the late G and H models of the Mark IV had been fitted with extra sheets of armour-plate at the front and over the tracks, and even many of the obsolescent Mk III tanks had been retrofitted with a long-barrelled 50mm gun, shells from which could also penetrate the armour of a T-34 at over a kilometre. Furthermore, the Zeiss binocular sights fitted in the new and up-gunned older tanks ensured more accurate fire than Soviet tank crews could achieve.