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. MI6 received the decrypts on Yugoslavia. The Military Intelligence section concerned with the Balkans (MI3b) received almost all the relevant decrypts, including diplomatic but not 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 Mihailović – 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 MI6, 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 clear 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’.
The British 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 Mihailović. 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 Mihailović. 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 all 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 MI3b reveals that their view, probably formed from the decrypts, was that Mihailović’s forces appeared to be fighting the communists rather than the Germans and that i
f that were true it was unlikely that the revolt could be maintained. The first doubts about Mihailović 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. Mihailović 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 Mihailović 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 Mihailović. 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, Mihailović 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 Mihailović since the spring but had been granted only limited access to Mihailović’s radio. He was now able to send reports more freely, but only from Mihailović’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 Mihailović 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 on 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 Mihailović 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 south-east of the Germans, allowing the Partisans to move eastwards across Herzegovina towards Montenegro.
The Bletchley Park Codebreakers Page 28
