Cripps, John (2001). "Mihailovic or Tito? How the Codebreakers Helped Churchill Choose (Chapter 13 pp237-263)". In Smith, Michael; Erskine, Ralph. Action This Day. London: Bantam. ISBN 0593 049101.



It is often assumed that the Bletchley Park codebreakers were only interested in the armed forces of Germany, Italy, Japan and, for a time, Russia. In fact, they attacked the codes and ciphers of the armed forces of a wide number of different countries, including Romania, Spain, Vichy France, and even China. They also broke a number of ciphers used by the various factions of the resistance in Yugoslavia. In this chapter, John Cripps examines the use of signals intelligence in determining which of the two guerrilla leaders fighting the Germans in Yugoslavia the Allies should back. The choice lay between the royalist Chetniks of General Draza Mihailovic and the communist Partisans led by Tito. There were already concerns over the way in which a postwar eastern Europe was likely to be dominated by the Soviet Union, so Churchill's choice of the communist Tito seems on the face of it a surprise. It has been suggested that James Klugmann, a communist activist and a KGB agent, who joined the Yugoslav section of SOE Cairo in 1942, was a prime mover behind the decision to back Tito rather than Mihailovic. Klugmann's role as a KGB agent is no longer in any doubt. He was instrumental in the conversion to communism of his Cambridge contemporary Anthony Blunt, the so-called Fourth Man in the Cambridge spy ring. He also played an active role in the recruitment of John Cairn cross, the Fifth Man and for a while a member of Bletchley Park's Hut 3. Klugmann's influence within the Yugoslav section is said to have been 'entirely disproportionate to his relatively junior rank'. He acted in the classic manner of a KGB agent of influence, taking every opportunity during briefings of other officers to lobby heavily on Tito's behalf and against Mihailovic. It is easy to see the attraction behind the idea that a KGB agent linked to the Cambridge Five so influenced his superiors that they persuaded Churchill to drop Mihailovic in favour of the communist Tito. But Cripps shows here that, whatever lobbying may have been taking place in Cairo, it would have been the overwhelming evidence of the Bletchley Park decrypts, Churchill's most favoured source of intelligence, which persuaded Britain's wartime leader that Tito and his Partisans were a much more effective, and reliable, ally in the war against Germany.

Michael Smith

Yugoslavia was invaded by the Axis on 6 April 1941. Its armed forces surrendered unconditionally eleven days l ater: it was then divided up between the occupying powers - Germany, Italy, Hungary and Bulgaria - with the largest part, although subject to military occupation by Germany and Italy, being declared the Independent State of Croatia. King Peter and the Yugoslav government fled, arriving in England in June to be feted as gallant heroes. This image was bolstered later in the year by the British government and the media when it became apparent that a major uprising had broken out in Yugoslavia. There were two major resistance movements fighting the Axis. One, the Chetniks, was led by Draza Mihailovic, a regular Yugoslav army colonel who had decided to fight on; the other, the communist Partisans, was led by Josip Broz, who operated under the nomme de guerre of Tito.

The British Government, at the time short of good news, and the Yugoslav government-in-exile, gave Mihailovic their enthusiastic backing and he was appointed Yugoslav Minister of War in January 1942. However, lack of resources and more important commitments elsewhere meant that support from Britain for the Chetniks was limited almost entirely to words rather than deeds. It was not considered appropriate to give succour to the Partisans who were described in a report by the Director of Military Intelligence, Major General Francis Davidson, to Winston Churchill in June 1942 as 'extreme elements and brigands'. But, less than eighteen months later, the Prime Minister decided, despite the outright opposition of Britain's ally, the Yugoslav government, to withdraw all support from Mihailovic and to supply the Partisans with materiel to enable them to prosecute their resistance. This assisted the Allies by tying down Axis forces which would otherwise be deployed in other theatres of the war, but had the inevitable consequence that Yugoslavia would become a communist state after the war. How did this volte-face in policy come about and what information provided the basis for this astonishing change of policy?

The British received intelligence about Yugoslavia during the war from a number of sources. Mihailovic established radio contact with his government and this link provided a certain amount of information, albeit entirely from Mihailovic's point of view. Reports were received from neutrals who had visited Yugoslavia and from Yugoslavs who had escaped the country. Neutral and Axis wireless station broadcasts, together with those from Radio Free Yugoslavia transmitting from the Soviet Union, were monitored and analysed, as were press reports. But as soon as the organization charged with fostering resistance movements, the Special Operations Executive (SOE), became aware of the revolt, it wanted to know more. It sent liaison officers, initially to Mihailovic. But when the British became disenchanted with Mihailovic, as they began to perceive his movement was less effective than the Partisans, the SOE sent missions to the Partisans. The first, led by Captain Bill Deakin, was sent to Tito's headquarters in May 1943. He was joined by Brigadier Fitzroy Maclean, a Conservative MP and former diplomat, the following September. Maclean subsequently reported to Anthony Eden, the British Foreign Secretary, and produced his 'blockbuster report', which recommended that the British should transfer support to Tito and sever their links with Mihailovic. In the absence until recently of Sigint on Yugoslavia, and in particular of decrypts of signals sent by the Wehrmacht's intelligence service, the Abwehr, it has generally been assumed that Maclean's report was the crucial element leading to the change of policy. The vast amount of Sigint relating to wartime Yugoslavia that has now been deposited at the Public Record Office shows that this was not the case.

The German occupying forces, and to a lesser extent the Italians, had little option but to use radio for communications between their units in Yugoslavia and to both the German Army Command in Salonika and the Oberkommando der Wehrmacht (OKW - the High Command of the German armed forces). The infrastructure of the country was primitive and was frequently disrupted by the resistance. Radio was, so they thought, a safer and more reliable form of communicating than post or courier. Decrypts were to show that the Abwehr had to rely to some extent on pigeons to send messages, probably not terribly dependable but more secure. Bletchley Park was able to decrypt many of the German signals, which led the authors of its internal history of Sigint in Yugoslavia and the Balkans to write in 1945 'that never in the field of Signals Intelligence has so much been decrypted about so little'.

Sigint provided intelligence from many different sources for the policy-makers, not least Churchill, who referred to it as Boniface, the mythical secret agent from whom, for cover purposes, it was supposedly obtained. Before the outbreak of hostilities in Yugoslavia, Bletchley Park had broken German railway Enigma, some air force Enigma ciphers and a very little army Enigma. Some intelligence was forthcoming about German plans for the invasion of Yugoslavia, including the build-up of forces and the exact date and time of the invasion, to the extent that the British were aware when the start time was brought forward, at the eleventh hour, by thirty minutes. After the occupation the amount of decrypted material gradually increased. The army established its headquarters for the Balkans (Army Group E), initially in Athens, and then in Salonika. Bletchley regularly read messages and situation reports passing between the Commander of Army Group E and his subordinate commanders, the German Generals in Zagreb and Belgrade, together with those of the German liaison office with 2nd Italian army, all of whom used Enigma. During 1943, it was also able to read some messages passed on the Fish links (which used teleprinter cipher machines) between Berlin and Salonika and Belgrade, and between Vienna and Salonika, as a result of the development of 'Heath Robinson'. Daily situation reports from Army Group E to Berlin were read regularly. German naval Enigma messages were decrypted, particularly after the Italian capitulation in September 1943 when the German Navy was trying to regain control of the Adriatic islands off the coast of Yugoslavia. Luftwaffe Enigma was also decrypted and some Italian Air Force messages using hand ciphers were read. The Abwehr had established a presence in Belgrade before the invasion and its radio messages were decrypted. After the occupation of Yugoslavia by the Axis, the Abwehr established offices throughout Yugoslavia, which used both hand ciphers and a special version of the Enigma machine to send reports of resistance activity to their area headquarters. Many messages from Abwehr officers or their agents were read. Others used the Abwehr links including the German consul in Dubrovnik, Herr Aelbert. In addition, the Nazi Party's intelligence service, the Sicherheitsdienst, operated in Yugoslavia: its messages were read, although in lesser volume than those of the Abwehr. In order to try to keep control, the Germans used various arms of their police service, often manned by local ethnic Germans, whose reports by radio were frequently decrypted. By the autumn of 1943, after the Allies had established themselves in southern Italy, a monitoring station was established in Bari, and later on the island of Vis, off the Yugoslav coast, which enabled local traffic between Chetniks, Partisans and Croatian units to be read. This supplemented intelligence from Chetnik and Partisan radio messages, which were summarized in German reports of their own decrypts of intercepted resistance radio messages. Despite Bletchley's own use of the Boniface cover, one of its internal reports described the German efforts to disguise the source of their intelligence, somewhat smugly, as being 'camouflaged rather transparently as information obtained from agents'.

Two other sources were identified and decrypted. Tito and the separate Slovene communist party kept in touch by radio with their masters in Moscow, the Comintern and its Bulgarian Secretary-General, Georgi Dimitrov. The volume of messages intercepted was not great but they yielded significant intelligence and continued with Dimitrov after June 1943, when the Comintern itself was dissolved. For a long time before the outbreak of war, the principal activity of GC&CS had been the decrypting of messages sent between diplomatic missions and their governments. This continued during the war. One of the most useful sources to the British, in terms of German policy in Yugoslavia, was the link between General Oshima Hiroshi, the Japanese ambassador in Berlin, and Tokyo. Oshima frequently reported on his conversations with Hitler and the German Foreign Minister, Joachim von Ribbentrop.

It was realized at a very early stage in the war that the decrypts provided the British with a priceless asset. Every effort was made to protect its security. By 1943, those who received Ultra were far greater in number than the thirty men who were its sole recipients (outside GC&CS and MI6) in 1940. By early 1943, Ultra was being sent to twelve destinations in the Middle East alone. Some of those who received intelligence derived from Sigint were not informed of its source, but as Montgomery's intelligence officer, Brig. E.T. Williams, has written, they must have guessed that it came from wireless intercepts. Nevertheless, some of those responsible for policy, and not just that on Yugoslavia, were denied access to the Bletchley Park material. The SOE in London did not receive any Sigint from any source during the war, let alone Enigma, although its office in Cairo did receive some locally decrypted Abwehr material on Yugoslavia in early 1943. Ml6 received the decrypts on Yugoslavia. The Military Intelligence section concerned with the Balkans (MI3b) received almost all the relevant decrypts, although probably not diplomatic or Comintern. The Directorate of Military Operations certainly had summaries from military intelligence. The Joint Intelligence Committee, whose task was to advise the military and the government on major matters of intelligence, had reports based on Sigint, as did the Chiefs of Staff. There were other recipients of Bletchley Park's output of Yugoslav Sigint. The Soviet agent John Cairncross passed some decrypts to the KGB when he was working in Hut 3 at Bletchley and later after being transferred to the MI6 headquarters at Broadway Buildings, which included both Abwehr and German Army signals from Yugoslavia. The evidence for this can be found in messages from the Comintern to Tito, giving information that was identical to Bletchley Park decrypts - it is unlikely that the source was the Russians' own decrypts. Thus Tito also benefited from Bletchley's work!

The Foreign Office received some heavily disguised intelligence reports based on Sigint, but did not receive any raw material, other than diplomatic decrypts, until the autumn of 1943. Therefore, the two principal organizations charged with the development of policy towards the Yugoslav resistance - the SOE and the Foreign Office - had either no access, or very limited access, to the decrypts. This inevitably led to much confusion in 1943 between those who wished to continue to support Mihailovic - the SOE and the Foreign Office - and those who wanted to switch support to Tito - SOE Cairo, MI6, the Directorates of Military Intelligence and Operations, the Chiefs of Staff and, ultimately, Churchill himself. The dilemma, after months of argument, was only to be resolved by the Prime Minister. Churchill received his daily box of raw decrypts, which frequently included detailed information about the actions of the resistance in Yugoslavia and Axis counter measures. Churchill, using his customary red pen, underlined or ringed items that caught his attention. He was, from time to time, briefed in detail in writing and given advice by military intelligence. He received summaries of decrypts from both military intelligence and air intelligence, some of which have survived, despite being marked 'to be destroyed'. Churchill received regular oral briefings from 'C', and from General Davidson, of which there is no record. It must be presumed that he also received written assessments from M16, but they have not been released.

Sigint provided a wealth of information about the events that occurred in Yugoslavia as they unfolded. German situation reports provided evidence of the activities of the resistance and of the Axis's attempts to counter them. From the decrypts, it was possible to discern the conflict that amounted to a civil war that raged between the Chetniks and the Partisans from the autumn of 1941 until the end of the war. The opinions held by German military commanders of their allies, the Italians and the Croats in the so-called Independent State of Croatia, were revealed, as were the Germans' own assessments of the Chetniks and the Partisans. The concern of the Germans, including Hitler, to preserve their vital mineral supplies from the Balkans and to keep open communications to Greece, together with their fears that the Allies might invade the Balkans in the summer and autumn of 1943, were described. Decrypts, particularly Abwehr, shed much light on the vexed question of collaboration between the resistance and the Axis. The subservience of Tito towards Dimitrov was confirmed. Decrypts also provided material on a lighter note. In April 1943, the Abwehr in Dubrovnik asked its office in Sarajevo to use their influence with the Italians on behalf of the owner of the Zwei Fischer restaurant to obtain permission for him to fetch a wagonload of wine for his customers.

In June and July 1941, foreign press reports and refugees provided some sketchy evidence that there was unrest in Yugoslavia and that the Serbs in the Independent State of Croatia were being displaced from their homes and killed by the Croats. At the end of July, the first substantive reports of this were received from decrypts. Abwehr reports referred to attacks on railway lines and confirmed that Serbs were being shot by the Croats. Italian aircraft were being deployed in Montenegro and in Croatia. German police reports revealed that the communists were making it difficult to maintain law and order along the border with the Reich. In early August, the first report was received that German soldiers had been killed and their bodies mutilated. One Abwehr report referred to a body of rebels who were well organized and 2,500-3,000 strong and added that, at that time, pacification of Bosnia was out of the question. During September, it was dear that the unrest was continuing. German army reports disclosed that towns were being threatened and that mopping-up operations were being carried out 'to crush the rebellion'. This report was sent to Churchill, who underlined these words in red.

Decrypts in October and November gave the names and locations of the ten Italian divisions based in Yugoslavia. They also disclosed that the Germans had four divisions deployed there. A series of decrypted situation reports provided evidence of the measures being taken by the Germans against guerrillas who were disrupting communications, seizing towns and attacking German, Italian and Croat forces. Decrypts also revealed that there were 'clashes' between Chetniks and Partisans and fighting between them. A decrypt of an Abwehr message at the end of November reported a meeting between Croat and Partisan representatives when the Partisans declared 'they would not lay down their arms until the end of the war and that they believed Russia would win in the end' .

TheBritish also had intelligence from Captain D. T. 'Bill' Hudson, an SOE officer who before the war had worked as an engineer in Yugoslavia. He was landed by submarine on the Yugoslav coast in September and briefly visited Tito's headquarters before joining Mihailovic. He was able initially to send back reports by radio but after November could not continue to do so for technical reasons and because of a breakdown in relations with Mihailovic. Intelligence assessments based on Sigint and Hudson's reports were sent to the Chiefs of Staff who expressed the opinion that 'the revolt was premature but the guerrillas have thrown their caps over the fence and must be supported by aU possible means'. The reality was quite different: the British in North Africa were hard pressed and had no materiel to send or the means to send it. A letter from MI6 to MBb reveals that their view, probably formed from the decrypts, was that Mihailovic's forces appeared to be fighting the communists rather than the Germans and that if that were true it was unlikely that the revolt could be maintained. The first doubts about Mihailovic were already setting in. Churchill, however, told the Chiefs of Staff on 28 November that 'everything in human power should be done to help the guerrilla fighters in Yugoslavia'. It became clear from the decrypts that, by the end of 1941, the Axis had got the upper hand. Mihailovic told his government by radio that he was going to ground. It seemed that for at least the foreseeable future there would be little resistance to the Axis from either the Chetniks or Partisans.

However, decrypts in early 1942 revealed that the Partisans were carrying on the fight. Reports were received of continuing sabotage that necessitated combined operations in January and February by German, Italian and Croat forces against the communists in Bosnia and Herzegovina. A series of situation reports from the German General Glaise von Horstenau, who was attached to the Croat government in Zagreb, revealed that there was resistance activity throughout Croatia and further west in Slovenia. An Abwehr officer reported from Sarajevo on 28 February that the Chetniks were being forced out of eastern Bosnia by the Partisans and that 'in future the communists are the only ones to be reckoned with'. At the end of March, a Luftwaffe report stated that the situation in the Italian area was becoming steadily worse. Information was sufficient for the officer responsible for the analysis of intelligence from Yugoslavia at MI3b, Major David Talbot Rice, to report that if Mihailovic was conserving his forces to strike when the time was right and if he did not receive support from the British, the initiative would pass to the Partisans. MI6 commented that the Partisans' policy was one of all-out offensive.

With the onset of spring, the Partisans continued their resistance. Railway Enigma provided evidence that bans had been imposed on the movements of trains on a number of lines due to sabotage. German army decrypts revealed that a special battle group had been formed to mount a joint operation with the Italians in western Herzegovina 'to smash the resistance as soon as possible'. Churchill continued to read his decrypts and, as a result, was sufficiently interested to ask for a report from General Davidson, which was delivered on 2 June. A map was attached illustrating the reports from Sigint for the five-day period from 26 to 30 May. The Prime Minister was advised that the 'wilder elements' among the Partisans 'embarrassed the enemy' by their attacks, but notwithstanding that Davidson was in no doubt that the British were right in backing Mihailovic. Churchill commented 'Good' and asked to be kept informed.

During the course of the summer, decrypts revealed that there were serious disputes between the Germans and the Italians. Von Horstenau reported that the Italians wished to withdraw much of their forces from the hinterland of Herzegovina, Bosnia and Croatia, leaving the Croat armed forces to deal with the resistance. The Germans, as a result, were particularly concerned about the security of supplies from one of their principal sources of bauxite, near Mostar, in Italian-occupied Herzegovina. Von Horstenau also reported that by August the Partisans had seized control of a large area of Croatia, centred on the town of Livno (at its largest, the area they controlled was about the size of Switzerland), and that the Croats would be unable to retake it. Although not revealed by decrypts, Tito was present and in charge of the area. The Commander of Army Group E, General Löhr, reported to OKW in Berlin that 'a really ticklish situation has arisen through the sudden departure of the Italians'. Reports were received of continued sabotage and clashes between the Partisans and the Axis. On 23 August, General Davidson wrote that the bulk of resistance activity was being carried out by the Partisans, but that, in his view, Mihailovic was preserving his forces 'to do their part when a general uprising could be staged'.

During September 1942, Hudson was joined by a radio operator. He had been back on speaking terms with Mihailovic since the spring but had been granted only limited access to Mihailovic's radio. He was now able to send reports more freely, but only from Mihailovic's headquarters, and about the Chetniks. This was virtually all the information that the SOE and the Foreign Office received; they decided to send a more senior officer, Colonel Bill Bailey, to join Hudson and to advise them on who to support and on the differences between Mihailovic and Tito. Bailey did not arrive until Christmas Day 1942.

In the meantime decrypts provided more intelligence. Von Horstenau demanded that the Italian High Command should take vigorous action to protect the bauxite area. The complete text of a message from the German Supreme Command, incorporating Hitler's decisions following a meeting with the Croat head of government on 23 September, was decrypted. Hitler would not countenance German reinforcements being sent but agreed to further armaments being supplied to the Croat army, now to be . placed under German command. Von Horstenau predicted that German soldiers would be 'needlessly sacrificing their blood' unless the Croats proved more capable than they had in the past. Further messages from the German Supreme Command were intercepted, stating that they were putting pressure on the Italians to clean up the Livno area while doubting that they had the means or desire to do so. On 17 October, a message from Hitler to Löhr was intercepted, demanding a full report about an attack on an antimony mine. Löhr then proposed that a joint German-Italian command be established, with himself as commander, and told German Supreme Command that the Italians were refusing to take part in any campaigning against the guerrillas during the winter.

Although not disclosed by decrypts, Hitler was sufficiently concerned about the situation in Yugoslavia to meet the Italian Foreign Minister, Count Ciano, in early December, when it was agreed that joint operations would take place in early 1943 to eliminate first the Partisans and then the Chetniks, who the Germans still feared had the potential to cause them problems. Before the campaign against the Partisans began, decrypts revealed its existence as Operation Weiss, and that it would be followed by a similar effort against the Chetniks, Operation Schwarz.

During the course of 1943, the volume of decrypts increased enormously. With the tide in the war having turned in the Allies' favour, and with the possibility of the invasion of Italy and Italian capitulation, there was renewed interest in stimulating the Yugoslav revolt. Churchill was sent decrypts relating to Weiss while 011 a visit to the Middle East. In late January, he received the complete German battle orders for Weiss; details of the German operational area in Croatia which included the Livno and bauxite areas; and the agreed plans for the disposition of Italian troops. The objective was to surround the Partisans, drive them against a blocking line provided by the Italians and then eliminate them. Churchill must have been excited when he learnt about these plans. At the time, he saw Bill Deakin, his pre-war research assistant who was then working for the SOE in Cairo. The operational head of SOE Cairo, Brigadier Keble, had previously worked for military intelligence in Cairo and was still receiving a limited number of Abwehr decrypts, which were analysed by Deakin and his superior officer Basil Davidson. Churchill demanded a report from Keble, who advocated that the Partisans should be contacted.

Talbot Rice reported on the Axis offensive to his superiors in military intelligence, who noted that the Partisans must have been causing the Axis considerable annoyance for them to mount an operation in mid-winter. He advised that if the Axis destroyed the ideological nucleus of the Partisans then it might be possible to reconcile the Partisans and the Chetniks; but if they escaped, their organization would have its prestige and influence enhanced. The decrypts revealed in great detail the progress of Weiss. The Partisans offered stiff resistance to the German ground forces and the Luftwaffe had to provide bombing support. By 16 February, the first stage of the operation was declared over, but reports indicated that elements of the Partisans had escaped the net, some moving towards the bauxite area and others re-establishing themselves in the cleared areas. Following Keble's report to Churchill, the Chiefs of Staff, who had been sent a copy, decided not to change policy and contact the Partisans, but not before Colonel Bateman of the Directorate of Military Operations had recommended that it was right to support the 'active and vigorous Partisans' rather than the 'dormant and sluggish' Chetniks. However, military intelligence was firmly of the opinion that support for Mihailovic should be maintained as were the Foreign Office and the SOE in London. The debate had now commenced in earnest, and decrypts were the only reliable source of information about the Partisans and the actions of the Axis.

The second stage of Weiss was now implemented. Decrypts provided evidence that the Partisans from the Livno area and local Partisans were advancing on the bauxite area. The Croat commander in Mostar complained that his forces were inadequately armed; that he was not being assisted by the Italians; and that his left flank was exposed. Abwehr decrypts confirmed that neighbouring towns had fallen to the Partisans. Decrypts revealed that proposals from Löhr to the Italians for the conduct of the second phase of Weiss were not agreed as the Italians wanted the Germans to provide more forces, which Löhr said he did not have. Decrypts did not reveal how this impasse was broken, but Löhr did say that he had used German troops in order to relieve the bauxite area. In fact, Hitler had sent him a directive to move on the bauxite area and temporarily to occupy it, which he did successfully. But the decrypts showed that the Partisans had again largely escaped destruction because once more the Italians had failed to move into position to the southeast of the Germans, allowing the Partisans to move eastwards across Herzegovina towards Montenegro.

The decrypts indicated that the situation on the ground was becoming ever more complex. As the Partisans moved to escape the Germans, the decrypts disclosed that they were confronted by Chetniks who were also intent on their annihilation. The Abwehr reported that the Chetniks in Herzegovina and Montenegro were preparing for large-scale operations against the Partisans at the end of March, with all men between the ages of thirteen and sixty being mobilized in the area for this purpose. The decrypts also revealed that there was a close relationship between the Italians and some Chetniks. This was already known to the British as a result of reports from Hudson, but the decrypts showed that the Italians were seeking the consent of the Germans for the use of Italian-officered Chetnik units against the Partisans. Löhr would not agree, but, as he could not stop the Italian plans, he requested that they make every effort to ensure the Chetniks would not come into contact with Germans advancing from the west, in case Italian officers came under German fire. Decrypts showed that the Italians were supplying the Chetniks with weapons and transporting them in lorries to get into position against the Partisans. In fact, during March the Germans did not advance against the Partisans or attempt any action against the Chetniks. Many years later, it became clear that there had been a ceasefire between the Germans and the Partisans, initially for the exchange of prisoners, but also because the Partisans were negotiating with the Germans for recognition as combatants, and for possible joint action against the Chetniks. Hitler put an end to the negotiations. Two Abwehr decrypts had, however, revealed that one of their agents, a German who reported as Dr Baux, was in negotiation with the Partisans, although it was not clear what the negotiations were about.

On 10 March, Talbot Rice prepared an appraisal on Weiss. General Davidson consequently advised the Chiefs of Staff and revealed the first signs of doubt about British policy with military intelligence stating that 'it was impossible to advise whether we should stick to our current policy of supporting Mihailovic but not the Partisans'. The SOE, military intelligence and the Foreign Office had not been greatly assisted by the reports from Bailey, who had only been able to suggest that the Partisans and the Chetniks should be allocated spheres of activity. Bailey himself accepted this was a forlorn hope. The Chiefs of Staff were provided not only with Talbot Rice's report, but the complete file on Weiss. As a result, they decided on 20 March that the Partisans should be contacted, despite opposition from the SOE in London, although to the delight of the SOE in Cairo. During this time, Churchill continued to receive decrypts relating to the major events that were taking place in Yugoslavia and also received a summary of the decrypts from 'C' in March, but the Prime Minister was yet to play a decisive part in the development of British policy.

During the German-Partisan ceasefire, Ultra enabled British intelligence to follow the course of a battle that ensued between the Chetniks and Partisans. In mid-March, a running battle took place along the Neretva river, which the Chetniks were unsuccessfully trying to prevent the Partisans from crossing. A decisive encounter took place around the Montenegrin town of Kalinovik between 20 and 25 March. Bailey had told the SOE that Mihailovic had left his headquarters on 16 March without telling Bailey where he was going or for what purpose. Decrypts reported that Mihailovic was directing the fight against the Partisans Jed by Tito around Kalinovik and that the Italians were transporting Chetnik reinforcements to the area. Numerous decrypted signals demonstrated that the fighting was severe. The town fell to the Partisans on 25 March, the battle against the Chetniks having been won. Dr Baux, who was on a mission in the area, reported that Mihailovic barely escaped being taken prisoner by the Partisans. Many Montenegrin Chetniks were said to have joined the Partisans, whose numbers in the area were estimated at 30,000. By early April, some of the Partisans were reported by the Abwehr to have reached the area in Montenegro around Mount Durmitor, having engaged Italian forces and put them to flight. They were said to have captured large quantities of food, arms, including heavy mortars, and ammunition. On 21 April, the first message from 'Walter' (Tito) to the head of the Comintern was intercepted by the British, although it was not decrypted until many months later. Tito claimed that a large number of regions were under Partisan control and that they were now organizing in the towns and villages in Herzegovina and Montenegro. The Abwehr reported that Tito, whose existence was mentioned in their messages, had established his headquarters near Foca.

A report, based on decrypts, was prepared for General Davidson and the Chiefs of Staff by MI3b on 23 April. It advised that Mihailovic had gravely prejudiced his long-term position by mobilizing his men for the campaign against the Partisans, and had lost command of Herzegovina and probably Montenegro. It concluded that, despite 200 miles of running battle with German forces, the Partisans had retained sufficient vigour and organization to defeat the Chetniks decisively, that the Germans were still trying to complete the destruction of the Partisans, and that Mihailovic and his Chetniks were in danger of becoming further identified with the Axis.

Decrypts also revealed the details of Operation Schwarz against the Chetniks. On 2 May, a message sent by General Alfred Jodl, Head of Operations at OKW, to Löhr on Hitler's instructions was intercepted. The operation was to be kept secret from the Italians, as they were not trusted to keep its existence from the Chetniks. An incident would be engineered to justify the Germans moving into Italian-occupied Herzegovina and Montenegro; the Chetniks would be rounded up and placed in prison camps rather than annihilated, as had been the plan with the Partisans in Weiss. Abwehr decrypts disclosed that fighting was still going on between Partisans and Chetniks and that one of Mihailovic's principal commanders, Pavle Djurisic, had fallen out with Mihailovic as he wished to assist the Germans against the Partisans, a course of action Mihailovic refused to contemplate. The Italians were still supplying the Chetniks and providing transport. On 13 May, the fabricated report that Chetniks had attacked German forces was decrypted as were subsequent German negotiations with the Italians who tried to protect as many of the Chetniks as they could when it became clear that the Germans were moving into their territory. The Germans advanced into Montenegro, taking Chetniks prisoner and disarming them. Decrypts showed that the German forces were also trying to surround and destroy the Partisans (including Tito) now concentrated around Mount Durmitor. As the Germans closed in, Deakin and an MI6 officer, a Captain Hunter, parachuted in to join Tito. Decrypts revealed that for the first time the Partisans were effectively surrounded and were at real risk of being wiped out. Abwehr and German army decrypts referred to the bitter fighting and repeated bombing of the Partisans. The battle was over by 14 June but it soon became clear, from the decrypts, that once again a substantial body of Partisans had escaped and that Tito had given orders that they should disperse and reform near Jajce in Bosnia. A decrypted report from Löhr on 22 June reported to the German High Command that 583 German soldiers and 7,489 Partisans had been killed, with the probability that the Partisans had lost another 4,000 men. Chetnik losses were put at 17, with nearly 4,000 taken prisoner. The contrast between the two resistance movements was stark.

Churchill had been kept informed from his own reading of the decrypts and no doubt from briefings. By this time the Allies had decided, at the Trident Conference in Washington in May 1943, that the second front would be l aunched across the Channel in 1944, but that Sicily could be invaded during that summer with further operations in the Mediterranean if subsequently agreed. Churchill argued in a note circulated at the end of the Conference for the occupation of southern Italy, which would enable munitions and commandos to be sent across the Adriatic to Yugoslavia. On 12 June, after reading his decrypts, he asked for a report from the intelligence services on Yugoslavia. At the time a debate was still raging as to whether the British should provide assistance to the Partisans now that they had been contacted. Probably due to incompetence, the report was prepared by the Foreign Office and the SOE in London, neither of whom had access to Sigint. It recommended the continuation of wholehearted support for Mihailovic, with contact with the Partisans being limited to trying to reconcile the two groups. The Chiefs of Staff wrote to the Foreign Office that they felt the report had given 'insufficient weight to the value of the Partisans as a fighting force against the Axis'. They stated that it was clear from 'information available to the War Office from Most Secret Sources that the Chetniks were hopelessly compromised with their relations with the Axis in Herzegovina and Montenegro and that . . . as the most formidable anti-Axis element outside Serbia the Partisans deserve the strongest support'. In their reply the Foreign Office grudgingly climbed down, agreeing to supplies being sent to the Partisans if the Chiefs of Staff were 'satisfied from information at their disposal' that the Partisans were sufficiently well organized and they would not hamper British efforts to unify the resistance.

Churchill had had enough: he summoned a meeting on 22 June to discuss Yugoslavia, stating: 'All this is of the highest importance.' He had also received that day the decrypt of the report by Löhr on Partisan and Chetnik losses. The meeting concluded that military assistance could be sent to the Partisans and support maintained for Mihailovic subject to conditions that he must actively offer resistance and refrain from collaboration with the Italians. Churchill now had the bit between his teeth. Three days before the invasion of Sicily, on 7 July, he sent a message to the British commander, General Alexander, saying that he presumed he had read the 'Boniface' about the heavy fighting in Yugoslavia. He also urged the seizing of the mouth of the Adriatic so that ships could be run into Dalmatian and Greek ports, although he recognized that 'this was hunting in the next field'. On 11 July, the Prime Minister, no doubt having chewed the cud further, instructed that a 2,000-3,000-word digest be made of the Sigint reports about Yugoslavia, Albania and Greece, 'showing the great disorder going on in these regions'. The digest is unfortunately not available, but after its receipt Churchill felt so impressed by its contents that he cabled Alexander to say that 'it gave a full account of the marvellous resistance by the followers of Tito and the powerful cold-blooded manoeuvres of Mihailovic in Serbia'. Having set out for Alexander the numbers of Axis divisions deployed, he wrote that, in his opinion, 'great progress lay in the Balkan direction'. Churchill was sufficiently enthused with the report to direct that a copy should be delivered by hand to Alexander. Churchill agreed to upgraded missions being sent to both Tito's and Mihailovic's headquarters. He personally briefed Fitzroy Maclean, who was being sent to the Partisans, dubbing him an 'ambassador leader'. But the Prime Minister clearly cared not one jot who was to be sent to the Chetniks. While he had not finally made up his mind whether to withdraw support from the Chetniks, it was clear that he was set on a course to provide the Partisans with the maximum support possible, whatever the political consequences for postwar Yugoslavia.

In the meantime, a message from Dimitrov to Tito in early July advised the Partisan leader to conserve his forces for future decisive fighting - a clear indication of the level of control exercised over him by Moscow. Abwehr decrypts indicated that Partisan groups were indeed making their way westwards from Mount Durmitor. During July, message after message was decrypted which indicated that the Germans feared an Allied invasion of the Balkans. The Abwehr advised Löhr that the Balkans would be 'the main object of an Allied attack'. The German Foreign Ministry advised its Consul in Istanbul that 'the Balkans would be the first to be invaded'. The head of the Italian Secret Service, General Cesare Arne, advised his German opposite number (he was not named in the decrypt but this was presumably Admiral Wilhelm Canaris, head of the Abwehr) that if Italy capitulated the Allies would turn their attention on the Balkans - his fears may have come about as a result of British disinformation. The possibility that the Germans feared Italian collapse was confirmed in a decrypted message from Ambassador Oshima to his government in Tokyo on 26 July, when he advised that Hitler had told him 'he recognised the possibility of Italian collapse and was preparing for the worst; and that Germany must strengthen her defences in the Balkans'. The Allies invaded southern Italy on 3 September. The final decision not to invade the Balkans had been taken at an Allied Conference in Quebec in August, which also decided that the Allies' involvement in that part of the world would be limited to supplying arms to the guerrillas, bombing strategic objectives, and minor commando raids.

Prior to this, the decrypts revealed that the Italians were effecting a withdrawal and that the Germans were positioning their limited forces to try to prevent a vacuum which could be exploited by the resistance or the Allies. On 7 August, the German Consul in Dubrovnik reported that the Italians were withdrawing from the hinterland and were moving Chetniks into position to cover their retreat. The German liaison officer with the Italian 2nd Army advised that his impression was that they were making 'a planned evacuation little by little'. Abwehr reports indicated that the Italians were offering arms to Chetniks to cover their withdrawal. Messages from the German naval commander were decrypted, which revealed his plans to seize Italian naval installations and ports. The German plans for reorganizing their army commands in north Italy and the Balkans were read. Decrypts disclosed movement of German forces into the Italian zone, and the occupation of Italian airfields. Some Chetniks, seeing the way the wind was blowing, sought to collaborate with the Germans. Intercepted reports from Dr Baux detailed the negotiations that he was having with the Chetnik leader in Herzegovina, Jevdjevic, who was offering to deploy 5,000-6,000 Chetniks in co-operation with the Germans against the Partisans. A Sicherheitsdienst report confirmed what the British also thought from their intelligence, that Mihailovic would only act if and when the Allies invaded the Balkans.

On 9 September, Italy capitulated. A decrypt of a message from the German Foreign Ministry announced that Hitler had foreseen Italy's collapse, that all measures had been taken and that German troops were marching. German Army Commander South East claimed on 12 September that 'the south east is firmly in our hands'. The decrypts revealed that the reality was different. The SS Prinz Eugen Division, recruited from local ethnic Germans, reported encountering stiff resistance from Italian forces who refused to surrender, although in Dubrovnik, the consul Aelbert signalled that after negotiations 28,000 Italians had decided not to fight. An earlier decrypt of a message sent by Aelbert to the commanding officer of the Prinz Eugen Division shed light on some of its activities. Aelbert complained that those reported to him included the shooting of '25 children as young as eight months', which he described as 'counterproductive' and 'having an extremely bad effect on the population'. The Prinz Eugen Division then fought a sixteen-day battle with Italian troops as it tried to move along the coast to take Split. In Montenegro, decrypts revealed that the Germans fought battles with the Italians until November. Decrypts also disclosed the actions of the resistance. The Partisans seized Split from the Italians, capturing large quantities of arms and supplies, and were joined by many Italians. On the German approach to the town, the Partisans moved away, the Abwehr reporting that Tito then intended to carry out 'major operations' in north Croatia and Slovenia. An Abwehr officer voiced the opinion, in a report on 21 September, that the 'total situation' in Croatia had got worse as a result of the actions of the Partisans. But decrypts also revealed that the Germans had largely dealt with the Italian problem by mid-October, when a report revealed that over 10,000 Italian officers and a quarter of a million men were being removed from Yugoslavia. There were no reports of Chetnik activity. The British knew from their liaison officers that Mihailovic had told his men not to carry out sabotage or engage the Germans. Decrypts also disclosed that the Germans were moving their killing squads, the Einsatzgruppen, into the former Italian zone to seize Jews and others.

Decrypts between Tito and Dimitrov subsequently revealed the Partisan leader's complaints that the British had not informed him of the date of Italian capitulation and that the British sent spies to the Partisans rather than supplies - a view that at that time was entirely correct, Maclean having arrived to join Deakin on 18 September. They also revealed that Dimitrov had told Tito the Russians would be sending him a mission. Tito's immediate response was to send a shopping list, including a request for 'several tens of suits for our generals and colonels'. Shortly afterwards, Dimitrov rebuked Tito for sending over-long reports.

At the end of September, Talbot Rice prepared a detailed assessment. He confirmed that there had been only isolated anti-German activity by Mihailovic, but that 'the heroes of the hour are undoubtedly the Partisans', who had seized large stretches of the coast. He advised that the Partisans were successfully embarrassing the Germans and that their 'military efforts deserve all the support we can give them'. He further recommended Mihailovic should be told to destroy German lines of communication in Serbia and be warned that if he failed to do so, Tito would be the sole recipient of British aid which they were at long last in a position to deliver. In the space of six months, the evidence from Sigint had completely changed the view of Talbot Rice, and MI3b.

Churchill was still very much interested in what was happening in Yugoslavia. On 9 September he minuted the Chiefs of Staff that, with the capture of southern Italy, munitions could soon be sent to the resistance. Although not now available, MI3b prepared a report for the Prime Minister on 12 October, no doubt on the same lines as their assessment at the end of September. Churchill was told by 'C' that the SOE had been asked to report on the provision of supplies to the resistance.

Numerous decrypts during October showed the continuing disorder in Yugoslavia and the Germans' attempts to counter it. German army and police reports referred to the Partisan threat to the major towns of Ljubljana and Zagreb and their interruption to railways radiating from the towns. Communists were resisting the German advance in Slovenia. A major operation was launched by the Germans in the area between Zagreb, Ljubljana and the Italian border at Trieste. According to German reports, the operation resulted in the death of 3,200 Partisans by mid November. The German commanders launched a series of operations to clear the Partisans from the remaining stretches of coast that they held, and from the Adriatic islands from which they threatened German shipping and supply routes. These operations were followed in detail by Bletchley Park. Air intelligence sent Churchill a breakdown of German efforts to capture the islands compiled from the decrypts. The German Admiral in the Adriatic reported their efforts as 'unsatisfactory'. Decrypts disclosed that the Germans were carrying out further operations to try and keep the bauxite flowing and at least gain control of communications in Herzegovina and Montenegro.

At the end of October, Churchill was sent a further assessment by MI3b, advising him in detail on the situation and concluding that 'the Partisans had been able to take over the initiative over practically all of Yugoslavia'. Mihailovic was not mentioned except for the fact that in Montenegro some of his supporters had deserted to the Partisans as 'the more active body'. More reports were received of Chetnik collaboration, the most significant of which was the full text of a treaty signed by one of Mihailovic’s principal commanders, Lukacevic, and the German Commander South East. Lukacevic agreed a cessation of hostilities in his area of southern Serbia and joint action against the Partisans. A full copy of the treaty was sent to Churchill.

Maclean delivered his report to Anthony Eden on 7 November, recommending all-out support for the Partisans. This had been the view of military intelligence since at least the end of September, when Talbot Rice's report backed the Partisans, and had also very probably been the view of MI6 for some time. The Chiefs of Staff advised Churchill on 11 November that measures to support the Partisans should be intensified. The question of what to do about Mihailovic had still to be decided. Churchill took the decision to abandon him and his movement. He announced his decision to Stalin - much to his surprise - and Roosevelt at the Tehran Conference at the end of November 1943. The existence of the principal source of Churchill's intelligence could not be revealed - hence the publicity given to Maclean's report - although it told Churchill nothing he did not already know. In fact, the Prime Minister was better informed than Maclean, who knew little of the detail of events over a wide area of Yugoslavia or of the Lukacevic treaty. In order to justify the decision to Parliament, to Allied governments, particularly those in exile, and to the press, Mihailovic was told to blow up two important bridges in Serbia or lose British support. As expected, he failed to act and British liaison officers were withdrawn from the Chetniks. At the same time a delegation from Tito arrived in Cairo to negotiate with the Yugoslav government in exile. The delegation was able to seek instructions from Tito by radio. Dimitrov advised Tito on the negotiations and how the delegation should play its hand. A series of decrypts revealed the exact advice given, particularly on the issue of the future of King Peter. Dimitrov advised Tito 'to show a necessary flexibility with reference to the question of the king to overcome certain difficulties on the side of the British and the Americans in the matter of their material assistance'.

It has been alleged by a number of commentators that 'a conspiracy' at SOE Cairo, having revealed the successes of the Partisans to Churchill, seduced him on to a path that was to lead to all-out support for the Partisans. It has been suggested that James Klugmann, a communist activist and KGB agent, who joined SOE Cairo in 1942, was the 'agent of influence' and prime mover behind the decision to back the Partisans rather than the Chetniks. However, in response to these 'wild allegations', Ralph Bennett, a former duty officer in Hut 3 at Bletchley, and Sir William Deakin and others later put forward the view that Sigint had provided the facts which persuaded Churchill, on military grounds and military grounds alone, to choose Tito in place of Mihailovic. It is now indeed clear from the decrypts that the Prime Minister was well aware of what was happening before he saw Deakin and Keble in Cairo and, while interested in what they had to say, was not manoeuvred into ultimate support for the Partisans by anything that emanated from SOE Cairo.

Churchill addressed the House of Commons for the first time in six months on 22 February 1944. He dealt with the situation in Yugoslavia at length. He was unable to justify the decision by reference to the decrypt and the advice he had received based on them, and therefore referred to reports received from Deakin and Maclean. In his peroration he advised that:

Our feelings, here, as elsewhere, I should like the House to see, follow the principle of keeping good faith with those who keep good faith with us, and of striving, without prejudice or regard for political affections, to aid those who strike for freedom against Nazi rule and thus inflict the greatest injury on the enemy.

With these few words, Churchill publicly dismissed Mihailovic and the Chetniks, and embraced Tito and the Partisans. The Partisans continued to harry the enemy, although the Germans were able to keep the bauxite flowing and to keep major communications routes open, allowing their forces in Greece to complete an orderly withdrawal in 1945 . The Partisans won the civil war and seized power in the immediate aftermath of German surrender. They hunted down Mihailovic and captured him. After a show trial he was shot in 1946.