Ultra - Use of Intelligence

Use of Intelligence

Most deciphered messages, often about relative trivia, were not alone sufficient as intelligence reports for military strategists or field commanders. The organisation, interpretation and distribution of intelligence derived from messages from Enigma transmissions and other sources into intelligence was a subtle business. This was not recognised by the Americans before the attack on Pearl Harbor, but was learnt very quickly afterwards.

At Bletchley Park, extensive indexes were kept of the information in the messages decrypted. For each message the traffic analysis recorded the radio frequency, the date and time of intercept, and the preamble—which contained the network-identifying discriminant, the time of origin of the message, the callsign of the originating and receiving stations, and the indicator setting. This allowed cross referencing of a new message with a previous one. The indexes included message preambles, every person, every ship, every unit, every weapon, every technical term and of repeated phrases such as forms of address and other German military jargon that might be usable as cribs.

The first decryption of a wartime Enigma message was achieved by the Poles at PC Bruno on 17 January 1940, albeit one that had been transmitted three months earlier. Little had been achieved by the start of the Allied campaign in Norway in April. At the start of the Battle of France on 10 May 1940, the Germans made a very significant change in the indicator procedures for Enigma messages. However, the Bletchley Park cryptanalysts had anticipated this, and were able—jointly with PC Bruno—to resume breaking messages from 22 May, although often with some delay. The intelligence that these messages yielded was of little operational use in the fast-moving situation of the German advance.

Decryption of Enigma traffic built up gradually during 1940, with the first two prototype bombes being delivered in March and August. The traffic was almost entirely limited to Luftwaffe messages. By the peak of the Battle of the Mediterranean in 1941, however, Bletchley Park was deciphering daily 2,000 Italian Hagelin messages. By the second half of 1941 30,000 Enigma messages a month were being deciphered, rising to 90,000 a month of Enigma and Fish decrypts combined later in the war.

Some of the contributions that Ultra intelligence made to the Allied successes are given below.

• In April 1940, Ultra information provided a detailed picture of the disposition of the German forces, and then their movement orders for the attack on the Low Countries prior to the Battle of France in May.
• An Ultra decrypt of June 1940 read KNICKEBEIN KLEVE IST AUF PUNKT 53 GRAD 24 MINUTEN NORD UND EIN GRAD WEST EINGERICHTET ("The Cleves Knickebein is directed at position 53 degrees 24 minutes north and 1 degree west"). This was the definitive piece of evidence that Dr R V Jones of scientific intelligence in the Air Ministry needed to show that the Germans were developing a radio guidance system for their bombers. Ultra intelligence then continued to play a vital role in the so-called Battle of the Beams.
• During the Battle of Britain, Air Chief Marshall Sir Hugh Dowding, Commander-in-Chief of RAF Fighter Command, had a teleprinter link from Bletchley Park to his headquarters at RAF Bentley Priory for Ultra reports. Ultra intelligence kept him informed of the German strategy, of the strength and location of various Luftwaffe units and often provided advance warning of bombing raids (but not of their specific targets). These contributed to the British success. Dowding was bitterly and sometimes unfairly criticized by others who did not see Ultra, but did not disclose his source.
• Decryption of traffic from Luftwaffe radio networks provided a great deal of indirect intelligence about the Germans' planned Operation Sea Lion to invade England in 1940 and, on 17 September 1940, about its cancellation.
• An Ultra message reported that equipment at German airfields in Belgium for loading planes with paratroops and their gear was to be dismantled. This was taken as a clear signal that Sea Lion had been cancelled.
• Ultra revealed that a major German air raid was planned for the night of 14 November 1940, and indicated three possible targets, including London and Coventry. However, the specific target was not determined until late on the afternoon of 14 November, by detection of the German radio guidance signals. Unfortunately, countermeasures failed to prevent the devastating Coventry Blitz. F. W. Winterbotham claimed that Churchill had advance warning, but intentionally did nothing about the raid, to safeguard Ultra. This claim has been comprehensively refuted by R V Jones, Sir David Hunt, Ralph Bennett and Peter Calvocoressi. Ultra warned of a raid but did not reveal the specific target. Churchill, who had been en route to Ditchley Park, was told that London might be bombed, and returned to 10 Downing Street so that he could observe the raid from the Air Ministry roof.
• Ultra intelligence considerably aided the British Army's victory over the much larger Italian army in Libya in December 1940 – February 1941.
• Ultra intelligence greatly aided the Royal Navy's victory over the Italian navy in the Battle of Cape Matapan in March 1941.
• Although the Allies lost the Battle of Crete in May 1941, the Ultra intelligence that a parachute landing was planned meant that heavy losses were inflicted on the Germans and that fewer British troops were captured.
• Ultra intelligence fully revealed the preparations for Operation Barbarossa, the German invasion of the USSR. Although this information was passed to the Soviet government, Stalin refused to believe it. The information did, however, help British planning, knowing that substantial German forces were to be deployed to the East.
• Ultra intelligence made a very significant contribution in the Battle of the Atlantic. Winston Churchill wrote "The only thing that ever really frightened me during the war was the U-boat peril." The decryption of Enigma signals to the U-boats was much more difficult than those of the Luftwaffe. It was not until June 1941 that Bletchley Park was able to read a significant amount of this traffic currently. Transatlantic convoys were then diverted away from the U-boat "wolfpacks", and U-boat supply vessels sunk. On 1 February 1942, Enigma U-boat traffic became unreadable because of the introduction of a different 4-rotor Enigma machine. This situation persisted until December 1942, although other German naval Enigma messages were still being deciphered, such as those of the U-boat training command at Kiel. From December 1942 to the end of the war, Ultra allowed Allied convoys to evade U-boat patrol lines, and guided Allied anti-submarine forces to the location of U-boats at sea.
• In the Western Desert Campaign, Ultra intelligence helped Wavell and Auchinleck to prevent Rommel's forces from reaching Cairo in the autumn of 1941.
• Ultra intelligence from Hagelin decrypts, and from Luftwaffe and German naval Enigma decrypts, helped sink about half of the ships supplying the Axis in North Africa.
• Ultra intelligence from Abwehr transmissions confirmed that Britain's Security Service (MI5) had captured all German agents in Britain, and that the Abwehr still believed in the many double agents which MI5 controlled under the Double Cross System. This enabled major deception operations.
• Deciphered JN-25 messages allowed the U.S. to turn back a Japanese offensive in the Battle of the Coral Sea in April 1942 and set up the decisive American victory at the Battle of Midway in June 1942.
• Ultra contributed very significantly to the monitoring of German developments at Peenemünde and the collection of V-1 and V-2 Intelligence from 1942 onwards.
• Ultra contributed to Montgomery's victory at the Battle of Alam el Halfa by providing warning of Rommel's planned attack.
• Ultra also contributed to the success of Montgomery's offensive in the Second Battle of El Alamein, by providing him (before the battle) with a complete picture of Axis forces, and (during the battle) with Rommel's own action reports to Germany.
• Ultra provided evidence that the Allied landings in French North Africa (Operation Torch) were not anticipated.
• A JN-25 decrypt of 14 April 1943 provided details of Admiral Yamamoto's forthcoming visit to Balalae Island, and on 18 April his aircraft was shot down, killing this man who was regarded as irreplaceable.
• The part played by Ultra intelligence in the preparation for the Allied invasion of Sicily was of unprecedented importance. It provided information as to where the enemy's forces were strongest and that the elaborate strategic deceptions had convinced Hitler and the German high command.
• The success of the Battle of North Cape, in which HMS Duke of York sank the German battleship Scharnhorst, was entirely built on prompt deciphering of German naval signals.
• Both Enigma and Tunny decrypts showed Germany had been taken in by Operation Bodyguard, the deception operation to protect Operation Overlord. They revealed the Germans did not anticipate the Normandy landings and even after D-Day still believed Normandy was only a feint, with the main invasion to be in the Pas de Calais.
• It assisted greatly in Operation Cobra.
• It warned of the major German counterattack at Mortain, and allowed the Allies to surround the forces at Falaise.
• During the Allied advance to Germany, Ultra often provided detailed tactical information, and showed how Hitler ignored the advice of his generals and insisted on German troops fighting in place 'to the last man'.
• Arthur "Bomber" Harris, officer commanding RAF Bomber Command, was not cleared for ULTRA. After D-Day, with the resumption of the strategic bomber campaign over Germany, Harris remained wedded to area bombardment. Historian Frederick Taylor argues that, as Harris was not cleared for access to ULTRA, he was given some information gleaned from Enigma but not the information's source. This affected his attitude about post-D-Day directives to target oil installations, since he did not know that senior Allied commanders were using high-level German sources to assess just how much this was hurting the German war effort; thus Harris tended to see the directives to bomb specific oil and munitions targets as a "panacea" (his word) and a distraction from the real task.