later changed its mind and tried in vain to get them back. It was at Bruno, on 17 January 1940, that the ex-Warsaw group broke its first wartime Enigma signal. By 11 March Col. Louis Rivet, head of the French secret service, was writing in his diary: ‘The decrypts of the Enigma machine are becoming interesting and numerous.’ During the months that followed, however, material was read far too slowly – out of ‘real time’ – to influence events on the battlefield. Instead, Allied intelligence officers strove to make sense of a jumble of humint warnings, of varying degrees of plausibility, about when Hitler intended to strike in the West.
The first of these had come in the previous November when Major Gijsbert Sas, Dutch military attaché in Berlin, received a dramatic tip-off from his friend Colonel Hans Oster of the Abwehr: the Wehrmacht, said Oster, would launch a full-scale offensive against the British and French armies on the 12th of that month. This coincided with several other identical or similar warnings – including an important one from Col. Moravec’s Czechs in London, relayed by their man in Switzerland from Agent A-54, the Abwehr’s Paul Thummel. When nothing happened on 12 November, the British and French chiefs of staff assumed that they were the victims of Nazi disinformation. The Dutch already suspected Sas of being a double agent, and the credibility of the other sources, including A-54, suffered accordingly. Yet the warnings were correct. Hitler had indeed intended to strike in November. He was enraged that his generals insisted upon a last-minute postponement until spring, because the army was unready to move. Here was a vivid illustration of a precept later advanced by a British Army intelligence officer: ‘Perfect intelligence in war must of necessity be out-of-date and therefore ceases to be perfect … We deal not with the true, but with the likely.’
The next excitement took place one day in January 1940: thick fog caused a German courier aircraft flown by Major Erich Hönmanns to forced-land in neutral Belgium. Local police arrested the pilot and his passenger, an officer named Reinberger, interrupting them as they attempted to burn papers they carried, and retrieved the charred sheets from a stove. Within forty-eight hours the French and British high commands were reading the Wehrmacht’s plan for its intended invasion of France and the Low Countries, focused on a thrust through Holland and Belgium. Here was a textbook example of a genuine intelligence coup, with wholly unhelpful consequences. The French were confirmed in their conviction that the Germans would attack through Belgium as they had done in 1914, and as all France’s deployments anticipated. The British suspected an enemy deception: the material seemed too good to be true. Guy Liddell of MI5 wrote wearily on 14 January: ‘A German aeroplane came down in Belgium … with certain papers found on the pilot indicating projected attack by the Germans on Belgium and Holland. It looks rather as if this may have been part of the scheme for the war of nerves.’ Cadogan at the Foreign Office described receiving ‘complete plan of German invasion of the Low Countries. Very odd. But one can’t ignore these things, and all precautions taken.’
Kenneth Strong wrote ruefully afterwards: ‘So often I have heard it said that if we only had the plans of the other side things would be simple: when they actually came our way we found great difficulty in persuading ourselves that they were genuine.’ Most important, however, the capture immediately forfeited all virtue, because the German proprietors of the plan knew that the Allies had it. Thus, Hitler insisted on changing the invasion concept, to thrust instead through the Ardennes, which proved the one authentic strategic inspiration of his life. Here was another critical lesson about intelligence, especially important for codebreakers: captured material became worthless if its originators discovered that it was in enemy hands.
Alexander Cadogan noted in his diary for 19 January 1940 that Stewart Menzies now seemed to expect the Germans to attack soon after 25 January, and added dismissively, ‘but he’s rather mercurial, and rather hasty and superficial (like myself!)’. If this remark somewhat short-changed the diarist, it was scarcely a ringing endorsement of ‘C’. There was one further strand: low-grade Abwehr messages decrypted by MI5’s Radio Intelligence Service offered indications about the looming onslaught. At that time, however, machinery was lacking to analyse such material, to feed it into the military command system and ensure that notice was taken by commanders. In that pre-Ultra universe, politicians, diplomats and generals were chronically sceptical about intelligence of all kinds. When a new warning reached MI6 via Moravec’s ‘London Czechs’ – that Abwehr officer Paul Thummel expected a great Wehrmacht thrust on 10 May, it vanished in the welter of ‘noise’ that spring.
The 9 April German invasion of Norway caught the Western Allies totally by surprise. Though no decrypts were available, the Admiralty ignored or misread plentiful clues about Hitler’s intentions. When the Wehrmacht’s amphibious forces began to land on the Norwegian coast, the Royal Navy’s major units were far away, awaiting an anticipated breakout into the Atlantic by German battleships. Through the weeks that followed, Wehrmacht eavesdroppers easily tracked the British brigades struggling to aid the little Norwegian army, while intelligence learned little or nothing about the invaders’ lightning movements.
On 10 May 1940, Hitler launched his Blitzkrieg in the West. The panzers swept through the Ardennes, across the Meuse, and thence to the Channel coast and into the heart of France. Much of the information sent back from the front by French units was so fanciful that a headquarters intelligence officer, André Beaufre, dismissed it contemptuously as a ‘fiction flood’. Gen. Maurice Gamelin, the Allied commander-in-chief, rejected every report that contradicted his obsessive belief that the Germans still planned to make their main attack through Belgium.
The campaign proved a triumph for the German army’s intelligence department, as well as for its generals. An anglophile and bon viveur, Lt. Col. Ulrich Liss, headed Foreign Armies West – FHW, the Wehrmacht’s principal intelligence evaluation department. Liss, who was exceptionally able and energetic, called sigint ‘the darling of all intelligence chiefs’, because it could be trusted as spies could not – and in May 1940 the best of it was in the hands of his own staff. During the long, static winter, German interceptors had identified the locations of most of the Allies’ formations, much assisted by the insecurity of the French army’s wireless-operators and headquarters staffs, who often discussed plans and deployments in plain language. Col. Handeeming, radio intelligence’s interception chief with Army Group A, was explicitly commissioned to monitor the French Seventh Army’s advance into Belgium, which he did with notable efficiency.
Liss’s men also benefited from securing vast numbers of Allied prisoners. All armies gleaned much from PoW interrogation. Throughout the war, even if few prisoners knowingly betrayed secrets, amid the shock of capture most gave their captors more than the regulation ‘name, rank and number’. Rommel’s intelligence staff found that British prisoners talked freely until a late stage of the North African campaign. One of Montgomery’s officers enthused to the Germans, with almost insane indiscretion, that Eighth Army’s radio monitoring service was ‘brilliant in every respect’. A German wrote that British officers were repeatedly captured ‘carrying important lists, codes and maps’. It was a standard technique for intelligence officers to engage PoWs in apparently innocent conversation about non-military subjects. The Wehrmacht’s ‘Guidelines for the interrogation of English prisoners of war’, dated Berlin, 16 April 1940, urged commanders whenever possible to use interrogators familiar with Britain and the British. ‘If cordially addressed,’ said the briefing note, ‘every Englishman will at once answer all questions entirely frankly.’ Beyond immediate tactical issues, the Intelligence Department advised:
Special value is set on probing prevailing economic and social circumstances in England. Answers to the following questions are useful:
a) What are you told about Hitler?
b) What are you told about the Nazis?
c) What are you told about the Gestapo?
d) What are you told about the Jews?
e) What are you told about food conditions in Germany?
f)
