FINEST HOUR 150, SPRING 2011
BY MARTIN GILBERT
The Rt. Hon. Sir Martin Gilbert CBE has been the official biographer of Sir Winston Churchill since 1968, and has published almost as many words on his subject as Churchill wrote. Sir Martin is an honorary member of The Churchill Centre and has been a contributor to Finest Hour for nearly thirty years. For further information see http://www.martingilbert.com. Part I of this article appeared last issue
At Hitlerʼs greatest expectation of triumph, the fruits of British Signals Intelligence became a precious metal in Soviet Military resistance. Decrypts also helped Britain support Balkan allies, by relaying German military dispositions to the Yugoslav and Greek partisans.
AIDING THE SOVIET UNION
Throughout the spring of 1941, Enigma decrypts made it clear that it was against the Soviet Union—Germany’s partner for the previous twenty months—that Hitler intended to turn next. On March 30th, Churchill wrote to Anthony Eden: I told C [Brigadier Stewart Menzies, Chief of MI6, the British Secret Intelligence Service] to send you substance of sure information lately received in this No. JQ/803/T2. My reading is that the bad man concentrated very large armoured forces, &c., to overawe Yugoslavia and Greece, and hoped to get former or both without fighting. The moment he was sure Yugoslavia was in the Axis he moved three of the five panthers towards the Bear believing that what was left would be enough to finish the Greek affair. However, Belgrade revolution upset this picture and caused orders for northward move to be arrested in transit. This can only mean in my opinion intention to attack Yugoslavia at earliest or alternatively act against the Turk. It looks as if heavy forces will be used in Balkan Peninsula and that Bear will be kept waiting a bit. Furthermore, these orders and counter-orders in their relation to the Belgrade coup seem to reveal magnitude of design both towards southeast and east. This is the clearest indication that we have had so far.
The defeat of the Soviet Union would enable the full weight of German power to be turned on Britain: with control of Russian oil supplies, raw materials, steel and munitions being massively in Germany’s favour. On 3 April 1941, while Hitler’s forces were making their final preparations for the invasion of Yugoslavia and Greece, Churchill took a calculated risk in sending Stalin information, based on Enigma, relating to German intentions against the Soviet Union. To guard the highly vulnerable source of the information, he pretended that this source was a British agent—an individual—not Germany’s own top-secret Signals Intelligence communications system.
The message sent to Stalin was emphatic and urgent:
I have sure information from a trusted agent, that when the Germans thought they had got Yugoslavia in the net, that is to say, after March 20 [the day of the signing of the Yugoslav pact with Germany], they began to move three out of the five Panzer divisions from Roumania to Southern Poland. The moment they heard of the Serbian revolution [the Yugoslav renunciation of the pact with Germany] this movement was countermanded.
Churchill ended his message to Stalin: “Your Excellency will readily appreciate the significance of these facts.” Stalin was not the only foreign recipient of Churchill’s Enigma-based information that week. On April 4th, the day after his telegram to Stalin, Churchill sent a message to General Dusan Simovitch, the leader of the new Yugoslav Government:
From every quarter my information shows rapid heavy concentration and advance towards your country by German ground and air forces. Large movements of air forces are reported to us from France by our agents there. Bombers have even been withdrawn from Tripoli according to our African Army Intelligence.
Although Churchill could not say so, “my information” was not from “our agents” or “African Army Intelligence” but Luftwaffe Enigma messages decrypted at Bletchley Park.
Enigma could reveal German intentions; but this knowledge could not forestall those intentions. On Easter Monday the Germans bombed Belgrade. British troops were rushed to Greece. Germany, with Italian and Bulgarian military and air support, swiftly overran both Yugoslavia and Greece, and turned its preparations, as Churchill had forecast, against the Soviet Union.
Stalin made no acknowledgment to Churchill for sending him on April 3rd the Enigma-based information that intimated the German intention to attack the Soviet Union. But Churchill instructed the Foreign Secretary, Anthony Eden, to pass on to the Soviet Ambassador in London, Ivan Maisky, several further messages, likewise derived from Enigma, giving details of German military and air moves and preparations towards the Soviet frontier. The most detailed, and important message was transmitted from Maisky to Moscow on 10 June 1941. It gave the Soviet General Staff a list of German troops concentrated on the German-Soviet border, identifying all German units.
Eleven days later, on 22 June 1941, Germany invaded the Soviet Union. Churchill made an immediate commitment to do whatever could be done to sustain the Soviet Union in its struggle. Signals Intelligence was a crucial and integral part of that commitment. Two days after the German invasion, Brigadier Menzies asked Churchill if he should pass on to Stalin—without revealing their source— the summaries of all Enigma decrypts bearing on the German intentions, strategy and tactics on the Eastern Front. Churchill gave his approval, noting on Menzies’ request: “Providing no risks are run.”
“Stalin rarely bothered to reply, but his commanders-in-chief took action on the basis of every Enigma-based communication….There were many occasions when the cryptographers at Bletchley Park—who did not have to leave their command posts to visit troops at the front —had already decrypted those messages, and sent them to Moscow, and Moscow had sent them to the commander-in-chief facing the German troops, even before the German commander returned to his command post and was given them.”
On 27 June 1941, within a week of Hitler’s invasion of Russia, there was a British cryptographic success at Bletchley Park in breaking the German Army Enigma key used on the Eastern Front. Known as “Vulture,” this key provided British Intelligence with daily readings of German military orders sent from Berlin to the Eastern Front. On June 28th, the day after Bletchley’s success, Churchill gave instructions that Stalin was to be given this precious Intelligence. From that day, an officer in British Military Intelligence serving in the British Military Mission in Moscow was sent—by British radio cypher—regular warnings of German strategic intentions and tactical orders, and was instructed to pass them on to Soviet Intelligence.
Thus, at Hitler’s greatest expectation of triumph, the fruits of British Signals Intelligence also became a precious metal in Soviet military resistance.
Enigma-based information useful to the Soviet Union was continuously sent on Churchill’s instructions to the British Military Mission in Moscow, where a special liaison officer would take it to the Kremlin for the head of Soviet Military Intelligence. One of these officers was the future Sovietologist and historian Edward Crankshaw.
“I have sure information from a trusted agent that when the Germans thought they had got Yugoslvaia in the net…they began to move three out of the five Panzer divisions from Roumania to Southern Poland. The moment they heard of the Serbian revolution [renouncing the pact with Germany] this movement was countermanded….Your Excellency will readily appreciate the significance of these facts.”
—Churchill’s telegram to Stalin, 3 April 1941
In the first week of July 1941, cryptographers at Bletchley learned from Enigma that German Intelligence on the Eastern Front was breaking into two Soviet channels of communication. The Germans were reading certain Russian Air Force coded messages in the Leningrad area, and were decrypting Russian naval signals in the Baltic. This information was passed on to Moscow on 7 July 1941, alerting the Soviet General Staff to this gap in their security. A week later, on July 14th, the disposition and order of battle of the German forces was transmitted to Moscow.
On July 16th, an appreciation of German plans against Smolensk and Gomel, together with details of German air force targets behind Russian lines, were transmitted from Bletchley to Moscow. The next day it was a German order —as a result of heavy German casualties and problems of adequate air cover—to slow down the advance. This order gave the Red Army its first sense of success, and also a chance to regroup, knowing that its forces would not face a surprise attack.
In mid-July 1941, as German troops drove towards Leningrad and Moscow, Churchill pressed Brigadier Menzies to send as much Enigma-based Eastern Front material as possible to Stalin. The important decrypt CX/MSS/59/T10, setting out operations that were to take place on the Eastern Front on July 16th, had been sent at 7:30 pm on 15 July 1941. The summary as submitted to Churchill read: “Russians threatened by envelopment at Smolensk. Support of 4th Panzer Army (Armée) with main battlefront at Smolensk. Russians are to be prevented from withdrawing. Railways in the rear to be bombed.”
Menzies replied to Churchill: “I am of the opinion that the source would definitely be imperilled if this information was passed to Moscow in its present form, as it would be impossible for any agent to have secured such information regarding operations for the 16th July. I have, however, arranged with the War Office for the gist to be incorporated with other material.”
Menzies went on to point out to Churchill that the head of the British Military Mission to Moscow, General Mason-MacFarlane, had been instructed “to inform the Russians that we possess a well-placed source in Berlin who has occasional access to operational plans and documents. This explanation has been accepted by the Russians. I have, however, refused to furnish them with detailed identifications, which might well arouse their suspicions as to the real origin of the information, for they would appreciate the impossibility of being able to furnish us with any identifications on the Western Front.” With his message, Menzies
sent Churchill “a sample of the type of information which has been passed and which should prove of considerable assistance to the Russian General Staff.”
On 9 September 1941, as German forces pressed towards Moscow, the German orders for the final assault on Moscow were decrypted at Bletchley Park. These orders were at once radioed to the British Military Mission in Moscow, and then taken to the Kremlin, more then three weeks before the actual assault began.
When it became clear on September 20th, through Enigma, that the Germans planned to launch an all-out assault on Moscow in twelve days’ time, Churchill authorized the dispatch of a warning to Stalin, through the British Military Mission in Moscow. Eight further Enigma-based warnings were sent to Moscow in the following four days, giving the Soviet High Command more than a week’s notice of German intentions, dispositions and movements on all sectors of the Moscow Front, and the location and strength of German ground formations assembling in the Smolensk area.
Reading a decrypt giving details of the German armoured and motorized divisions about to be committed to the battle for Moscow, Churchill wrote on 2 October 1941 to Brigadier Menzies: “Are you warning the Russians of the developing concentrations,” and he added: “Show me the last five messages you have sent.”
On 2 January 1942, British cryptographers broke the Enigma key known to Bletchley as “Kite.” This key contained the German Army’s most secret supply messages between Berlin and the Eastern Front. In February they broke “Orange Two,” which carried all top-secret messages between Berlin and the Waffen SS units fighting on the Eastern Front.
During the first week of March 1942, Enigma decrypts revealed the scale, direction and date of the second German summer offensive against the Soviet Union. These included German Air Force intentions, operational orders, and the fortification of aerodromes in the East. Also revealed, through a diplomatic decrypt, was Japan’s inability, because of a shortage of ships and aircraft, to help Germany by attacking the Soviet Union in the Far East, something Hitler was pressing for. Churchill noted on this latter decrypt that it should be passed to Roosevelt.
Another vital decrypt that was passed to Stalin was an Enigma message sent on March 3rd, and decrypted at Bletchley two days later, ordering the transfer of German anti-aircraft units in Romania to the Ukraine. This was followed on March 7th by decrypts of heavy German military rail movements from Romania to the Eastern Front, the despatch on May 10 of German bomber and dive bomber units to the Russian Front, and a German Air Force report, also decrypted on March 10, giving details of Soviet troop concentrations.
On receipt of this information from Britain, the Russians were able to make new dispositions, in greater secrecy. If that secrecy were to be compromised, Enigma would reveal it.
On March 12th, Churchill assured Stalin that, in order to help the Soviet Union meet this impending attack, he had given “express directions” that British supplies to Russia “shall not in any way be interrupted or delayed.” Churchill also gave orders that day that, to draw back German resources from the Eastern Front during the German offensive, the British bombing offensive over Germany would be intensified “both by day and night.” As Churchill explained two days later, in a message to the head of the British General Staff Mission in Washington, his policy was “taking the weight off Russia during the summer months by the heaviest air offensive against Germany which can be produced.”
On 23 May 1942, with Churchill’s approval, the Soviet High Command were sent details, culled from Enigma, of precisely where the German summer offensive against the Soviet Union would be launched, and in what strength. During the second week of July 1942, when a change of strategy was decided upon in Berlin, with armoured forces ordered forward towards Stalingrad, the details of this revised plan were sent from Berlin to the German military and air commanders-in-chief by Enigma signals. Both the recipients of this order, the German commanders-in-chief on the Eastern Front, and the British cryptographers at Bletchley Park, decrypted this change of plan simultaneously.
From Britain, the new orders were sent on July 13 to Moscow. From Moscow they were transmitted that same day by secure radio link to the newly appointed commander of the Stalingrad Front, Marshal Timoshenko. The Germans never knew that their plan was in the hands of their enemies. On the following day, 14 July 1942, the three German armies in southern Russia received from Berlin their precise objectives, likewise sent through Enigma. These objectives, decrypted at Bletchley Park, were also sent at once to Moscow, and on to Timoshenko.
Shortly after Churchill’s return from his first Moscow visit in August 1942, the seventeenth Arctic convoy, PQ 17, was attacked by German air and submarine forces. Of the forty merchant ships in the convoy, nineteen were sunk. Ironically, the tragedy of PQ 17 had been caused by Enigma, since the convoy’s escorts had been forced to scatter once it was revealed through Enigma that Germany’s three largest warships were about to emerge from their Norwegian Arctic bases, to attack. There was no way that the British convoy escort could outmatch these three naval giants or even stave them off. To avoid a total slaughter, the convoy was ordered to scatter.
On 30 September 1942, Churchill learned from an Enigma decrypt of a German plan for naval action on the Caspian Sea, as soon as German troops had crossed the Caucasus. He immediately sent a clear summary to Stalin. “I have got the following information,” he wrote, “from the same source that I used to warn you of the impending attack on Russia a year and a half ago. I believe this source to be absolutely trustworthy. Pray let this be for your own eye.” The information read:
Germans have already appointed an Admiral to take charge of naval operations in the Caspian. They have selected Makhach-Kala as their main naval base. About twenty craft including Italian submarines, Italian torpedo boats and mine-sweepers are to be transported by rail from Mariupol to the Caspian as soon as they have got a line open. On account of the icing-up of the Sea of Azov the submarines will be loaded before the completion of the railway line.
“No doubt,” Churchill wrote to Stalin, “you are already prepared for this kind of attack.” It seemed to Churchill “to make all the more important” the plan to reinforce the Soviet Air Force in the Caspian and the Caucasus theatre by twenty British and American squadrons. “I have never stopped working at this,” Churchill added, “since we were together and I hope in a week or so to have the final approval of the President and to be able to make you a definite joint offer.”
Churchill understood that every fragment of information on German military and air preparations and activities could be of inestimable value to the Soviet High Command, as daily decrypts showed that the German forces were facing a fierce opponent in southern Russia, and that there had been a setback in German plans there. “My latest information,” Churchill telegraphed to Stalin on October 8, “shows that the German plans for sending shipping to the Caspian have been suspended.”
The Soviet Union was to be the beneficiary of Enigma, and Churchill’s vigilance to Soviet needs, until the end of the war. Central to this effort was Colonel Tiltman, one of whose most important achievements came in September 1942, when he helped to break the German teleprinter cypher system known at Bletchley as Tunny— another word for tuna.
Unlike Enigma, Tunny carried a considerable amount of strategic Intelligence, while Enigma more often yielded tactical or operational Intelligence. Between November and December 1942, at the height of the Battle for Stalingrad, this resulted in an estimated 870 decrypts yielding 4.5 million letters of text, from four keys. By 1945 the figures had increased dramatically: between 1 January and 8 May 1945, Bletchley broke 374 keys—by then changing with increasing frequency—with the help of the Colossus electronic codebreaking machines: 4500 messages in all, containing 22 million letters were read in that period.
Churchill ensured that Stalin was apprised of German intentions on the Eastern Front without fail or delay. Enigma also enabled Churchill to intervene on Russia’s behalf in late October and early November 1942, at the height of the battle of Stalingrad. Because Enigma revealed the full extent of Germany’s commitment, and entanglement, in the East, Churchill timed a series of military initiatives in the West in such a way as to force the withdrawal of vital German war material from the East. The first of these initiatives was Montgomery’s attack on the German forces inside Egypt, at El Alamein, on October 23rd; then, two weeks later, on November 8th, Operation Torch, the Allied amphibious landings in North Africa.
These major African battles forced Hitler to transfer aircraft from the Eastern Front at a time when they were most needed in the East. In the immediate aftermath of the North African landings, 400 of the 500 German warplanes moved to Tunisia were brought from Russia, as were several hundred transport aircraft which had been supplying the German forces surrounded at Stalingrad. As a result of the precipitate transfer of these transport aircraft, German bombers had to be pressed into service at Stalingrad in their stead. Enigma revealed to the British, and through them to the Russians, just what a setback the fighting in North Africa was to the German resources on the Eastern Front.
Commenting on the unforeseen, and unfortunate, switch of aircraft at Stalingrad, Marshal Goering later wrote: “There died the core of the German bomber fleet.”
On November 7th, the day before the Torch landings, Churchill learned of German plans to bomb Soviet oil installations at Baku. He at once passed on this information to Stalin. “Many thanks for your warnings,” Stalin replied. “We are taking the necessary measures to combat the danger.” This was one of the very few times when Stalin bothered to reply, although his commanders-in-chief took action on the basis of every Enigma-based communication.
On 19 November 1942 the Red Army launched its counter-offensive north of Stalingrad. Throughout the battle, Britain sent Russia tactical Intelligence derived from the minute-by-minute operational orders of the German Army and Air Force. Sometimes a German commander could not be at his command post for several hours, as he had to be with his men at the front. Only on returning to his command post was he given his latest batch of operational orders.
There were many occasions when the cryptographers at Bletchley Park—who did not have to leave their command posts to visit troops at the front—had already decrypted those messages, and sent them to Moscow, and Moscow had sent them to the commander-in-chief facing the German troops, even before the German commander returned to his command post and was given them. Reading his daily box of Enigma decrypts, Churchill never relaxed his Russian vigilance. On 6 December 1942, during the Stalingrad battle, he wrote to Brigadier Menzies: “Has any of this been passed to Joe?” It had.
On 25 February 1943 there were two further breakthroughs in Allied help for the Soviet Union. First, that day, there was the breaking at Bletchley Park of the German “Ermine” key, used by one of the main German Air Force combat units on the Eastern Front. That same day, the start began of the first round-the-clock bombing offensive against Germany, whereby British bombers attacked by night and American bombers by day. For the Soviet war machine, the intensification of the Anglo-American bomber offensive was an important element in the constant pressuring and steady weakening of Germany’s war-making powers. “I hope,” Stalin telegraphed to Churchill on 27 March 1943, “that the air offensive against Germany will go on inexorably increasing.”
It did, with German Air Force Enigma messages providing Bletchley Park, and Bomber Command’s Commander-in-Chief, Sir Arthur Harris, with a daily indication of where the German fighter and anti-aircraft forces were most stretched, and therefore most vulnerable.
As the Germans prepared their third Eastern offensive, against the Soviet forces in the Kursk Salient, more and more of the actual German orders for the planned attack were decrypted at Bletchley. Once more, the British were able to alert Soviet Military Intelligence. One of the most important decrypts to be shown to Churchill was a Tunny decrypt of 25 April 1943. It contained a detailed German appreciation of the Soviet order of battle before the German offensive in the Kursk Salient.
Churchill made sure that this information was passed to Moscow, two months before the offensive was to open, together with detailed estimates, likewise based on the Germans’ own top secret signals, of the strength and composition of the German divisions deployed around the Salient or the Kursk and Orel pincer movements. This information alerted the Soviet High Command to exactly what the Germans knew of what was facing them, enabling the Soviet High Command to alter the balance of the facing forces to Soviet advantage. The Battle of Kursk was the last and fatal attempt by the German Army to continue its eastward advance.
The Soviet Union also made its contribution to the task of decryption. In June 1943, Soviet Intelligence captured two elements of the Enigma system, a code used by the Luftwaffe for air-to-ground signalling, and a naval Enigma machine. Shortly afterwards, Churchill sent several British Naval Intelligence experts to Murmansk to discuss with their Soviet counterparts how best to use the German air and naval messages thus procured. Later that summer, the British presented the Soviets with another captured Enigma machine, and a book of instructions for its use.
ASSISTING OCCUPIED YUGOSLAVIA
Churchill accepted that Enigma would determine many aspects of British war policy. In Yugoslavia in 1943, Enigma revealed a massive concentration of German and Italian troops encircling and moving in on Mount Dormitor. It was clear that a large hostile force was surrounding the mountain. Churchill, who was then in Cairo, agreed with an SOE proposal to parachute in a small team—two officers and a wireless operator—to the centre of the German encirclement, to make contact with the force that was the German target. The three volunteers found themselves with Josip Broz (Tito) and his partisans, in a fierce battle, but the partisans escaped the trap, and Britain began supporting Tito’s forces.
Enigma had helped Britain find, and support, a Balkan ally. One of the two British officers parachuted in on that first mission was Churchill’s former literary assistant, Bill Deakin; Churchill followed his activities through the Enigma decrypts, including his escape, with Tito, from the German trap.
On July 25th, Enigma decrypts had made it clear that as many as thirty-three German, Italian, Croat and Bulgarian Divisions were being held down in Yugoslavia, most of them by Tito’s partisans. Churchill therefore directed that a number of additional aircraft be used in the dropping of supplies: “This demand,” Churchill had explained to Ismay on the previous day, “has priority even over the bombing of Germany.”
The air resources needed to send up to 500 tons a month of arms and equipment to the Yugoslav partisans would be “a small price to pay,” Churchill told the Staff Conference, “for the diversion of Axis forces caused by resistance in Yugoslavia.” Every effort should be made, he said, “to increase the rate of delivering supplies. It was essential to keep this movement going.”
During July 1943, Enigma decrypts showed the pres- sure being exerted on German military dispositions by the partisans in both Yugoslavia and Greece, also the recipient of a British mission and supplies. On July 7th, Churchill telegraphed to General Alexander, Commander-in-Chief of the Allied Forces in the Mediterranean: “I presume you have read the ‘Boniface’ about the recent heavy fighting in Yugoslavia and the widespread sabotage and guerrilla beginning in Greece.” From Quebec, where he was with Roosevelt, Churchill telegraphed a week later to Alexander:
I am sending you by an officer a full account which I have had prepared from “Boniface” and all other sources of the marvelous resistance put up by the so-called Partisan followers of Tito in Bosnia and the powerful cold-blooded manoeuvres of Mihailovic in Serbia. Besides this there are the resistances of the guerrillas in Albania and recently in Greece.
The Germans had not only been reinforcing the Balkan peninsula with divisions, Churchill noted to General Alexander, “but they have been continually improving the quality and mobility of these divisions and have been stiffening up the local Italians.”
Basing his figures upon Enigma, Churchill informed Alexander that there were in Yugoslavia nine German, seventeen Italian, five Bulgarian and eight Croat divisions. On the Greek mainland, there were a further six German, eight Italian and two Bulgarian divisions. “The enemy,” he commented, “cannot spare these forces, and if Italy collapses the Germans could not bear the weight themselves.”
While he was staying at Roosevelt’s home at Hyde Park, on the Hudson River, Churchill wrote to Roosevelt about Yugoslavia. A series of Enigma decrypts had revealed the murder by German forces, not only of Tito’s partisans in combat, but of several thousand Yugoslav civilians as reprisals.
“I am not sure that you people have quite realized all that is going on in the Balkans,” Churchill told Roosevelt, “and the hopes and horrors centred there. You might find it convenient to keep it by you. Much of it is taken from Boniface sources, and it certainly makes one’s blood boil, I must add.”
Churchill also sought to put Roosevelt’s mind at ease. “I must add,” he wrote, “that I am not in any way making a case for the employment of an Allied army in the Balkans but only for aiding them with supplies, agents and Commandos.”
1. Decrypt summary JQ/803/T2.
3. The Soviet Union.
4. “Most Secret”, 30 March 1941: Churchill papers, 20/49
5. Telegram of 3 April 1941: Premier papers, 3/170/1.
6. Message dated 4 April 1941: Churchill papers, 20/49.
7. In particular Enigma decrypts CX/JQ803, 808, 821, 822 and 849 (military movements) and 823 and 829 (air preparations), summarized in F. H. Hinsley and others, British Intelligence in the Second World War, Its Influence on Strategy and Operations, Volume 1, London, 1979, 371-72.
8. I am grateful to the Russian historian Colonel-General Dmitri Vokogonov for giving me access to this document in Moscow in the summer of 1995.
9. Secret Intelligence Service archives.
10. Decrypt CX/MSS/59/T10.
11.Secret Intelligence Service papers, HWI/14.
12. Secret Intelligence Service papers, HWI/14.
13. HW 1/381.
14. HW 1/383.
15. HW 1/386.
16. HW 1/138.
17. HW 1/390.
18. HW 1/392.
19. HW 1/401.
20. HW 1/402.
21. Prime Minister’s Personal Telegram No. 352 of 1942, 9 March 1942: Churchill papers, 20/132.
22. Prime Minister’s Personal Telegram No. 384 of 1942, 14 March 1942: Churchill papers, 20/88.
23. Secret Intelligence Service papers: HW 1/590.
24. Secret Intelligence Service papers: HW 1/710, 712, 713, 715, 718, 719, 721 and 722.
25. Prime Minister’s Personal Telegram, T.1270/2, “Most Secret and Personal”, 30 September 1942: Churchill papers, 20/80.
26. “Personal”, Prime Minister’s Personal Telegram 1363 of 1942,8 October 1942: Churchill papers, 20/88.
27. Tunny was an on-line encyphered teleprinter (Schlüsselzusatz 40 or SZ-40) designed by the Lorenz Company.
28. Ralph Erskine and Peter Freeman, “Brigadier John Tiltman: One of Britain’s Finest Cryptographers,” Cryptologia, October 2003.
29. “Personal,” Kremlin, Moscow, 7 November 1942: Churchill papers, 20/82.
30. Secret Intelligence Service archive, series HW1/1183.
31. “Personal and Most Secret,” Kremlin, Moscow, 27 March 1943: Churchill papers, 20/108.
32. Erskine and Freeman, “Brigadier John Tiltman,” op. cit.
33. Staff Conference of 23 July 1943, Chiefs of Staff Committee No. 135 (Operations) of 1943, 23 June 1943: Cabinet papers 79/62. The Ministers present were Churchill (in the Chair), Lord Selborne and Lord Cherwell. Sir Alexander Cadogan represented Eden. Also present for the Yugoslav discussion were Major Morton and Lord Glenconner.
34. “Personal and Most Secret”, Prime Minister’s Personal Telegram No. 971 of 1943, 7 July 1943: Churchill papers, 20/114.
35. “Secret. For you alone”, Prime Minister”s Personal Telegram No. 1083 of 1943, 22 July 1943: Churchill papers, 20/115.
36. “Mr President,” 13 August 1943: Premier papers, 3/353, folios 92-93.26. “Personal”, Prime Minister’s Personal Telegram 1363 of 1942, 8 October 1942: Churchill papers, 20/88.