Editing Ultra (cryptography) (section)

==Use of intelligence==
Most deciphered messages, often about relative trivia, were insufficient as intelligence reports for military strategists or field commanders. The organisation, interpretation and distribution of decrypted Enigma message traffic and other sources into usable intelligence was a subtle task.

At Bletchley Park, extensive indices were kept of the information in the messages decrypted.<ref>{{cite web| title = Bletchley Park Archives: Government Code & Cypher School Card Indices | url = http://www.bletchleypark.org.uk/edu/archives/gccscoll.rhtm | access-date = 8 July 2010 | archive-date = 29 April 2011 | archive-url = https://web.archive.org/web/20110429032943/http://www.bletchleypark.org.uk/edu/archives/gccscoll.rhtm | url-status = dead }}</ref> For each message the traffic analysis recorded the radio frequency, the date and time of intercept, and the preamble{{snd}}which contained the network-identifying discriminant, the time of origin of the message, the callsign of the originating and receiving stations, and the [[Enigma machine#Indicator|indicator]] setting. This allowed cross referencing of a new message with a previous one.{{sfn|Welchman|1984|p=56}} The indices 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 ''[[Known-plaintext attack|cribs]]''.{{sfn|Budiansky|2000|p=301}}

The first decryption of a wartime Enigma message, albeit one that had been transmitted three months earlier, was achieved by the Poles at [[PC Bruno]] on 17 January 1940. 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{{snd}}jointly with PC Bruno{{snd}}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 [[bombe]]s 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.{{sfn|Hinsley|1993a}}

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.{{sfn|Winterbotham|1974|pp=27–31}}
* An Ultra decrypt of June 1940 read {{lang|de|[[Knickebein|KNICKEBEIN]] KLEVE IST AUF PUNKT 53 GRAD 24 MINUTEN NORD UND EIN GRAD WEST EINGERICHTET}} ("The [[Cleves]] {{lang|de|Knickebein}} is directed at position 53 degrees 24 minutes north and 1 degree west"). This was the definitive piece of evidence that [[Reginald Victor Jones|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.{{sfn|Jones|1978|p=92}} Ultra intelligence then continued to play a vital role in the so-called [[Battle of the Beams]].
* During the [[Battle of Britain]], Air Chief Marshal [[Hugh Dowding, 1st Baron Dowding|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 German strategy,{{sfn|Calvocoressi|2001|p=90}} and of the strength and location of various {{lang|de|Luftwaffe}} units, and often provided advance warning of bombing raids (but not of their specific targets).{{sfn|Lewin|2001|p=83}} These contributed to the British success. Dowding was bitterly and sometimes unfairly criticized by others who did not see Ultra, but he did not disclose his source.
* Decryption of traffic from {{lang|de|Luftwaffe}} radio networks provided a great deal of indirect intelligence about the Germans' planned [[Operation Sea Lion]] to invade England in 1940.{{sfn|Jones|1978|p=124}}
* On 17 September 1940 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.{{sfn|Winterbotham|1974|pp=56–58}}
* 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.{{sfn|Winterbotham|1974|pp=60–61}} This claim has been comprehensively refuted by [[R. V. Jones]],{{sfn|Jones|1978|pp=146–153}} Sir David Hunt,{{sfn|Hunt|1976}} Ralph Bennett{{sfn|Bennett|1999|p=64}} and Peter Calvocoressi.{{sfn|Calvocoressi|2001|p=94}} Ultra warned of a raid but did not reveal the target. Churchill, who had been ''en route'' to [[Ditchley|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 [[Operation Compass]] victory over the much larger Italian army in [[Libya]] between December 1940 and February 1941.<ref>{{cite web | title = Seventy Years Ago This Month at Bletchley Park: December 1940 | publisher = Bletchley Park National Codes Centre | url = http://www.bletchleypark.org.uk/content/archive/index/december1940.rhtm | access-date = 16 December 2010 | archive-date = 29 April 2011 | archive-url = https://web.archive.org/web/20110429032938/http://www.bletchleypark.org.uk/content/archive/index/december1940.rhtm | url-status = dead }}</ref>
* Ultra intelligence greatly aided the Royal Navy's victory over the Italian navy in the [[Battle of Cape Matapan]] in March 1941.{{sfn|Hinsley|1993|p=3}}
* Although the Allies lost the [[Battle of Crete]] in May 1941, the Ultra intelligence that a parachute landing was planned, and the exact day of the invasion, meant that heavy losses were inflicted on the Germans and that fewer British troops were captured.{{sfn|Winterbotham|1974|pp=67–69, 187}}
* Ultra intelligence fully revealed the preparations for [[Operation Barbarossa]], the German invasion of the USSR. Although this information was passed to the Soviet government,  [[Joseph Stalin|Stalin]] refused to believe it.{{sfn|Lewin|2001|p=104}} 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."{{sfn|Churchill|2005|p=529}} The decryption of Enigma signals to the [[U-boat]]s was much more difficult than those of the {{lang|de|Luftwaffe}}. It was not until June 1941 that Bletchley Park was able to read a significant amount of this traffic contemporaneously.{{sfn|Budiansky|2000|p=341}} Transatlantic convoys were then diverted away from the U-boat [[Wolfpack (naval tactic)|"wolfpacks"]], and the U-boat supply vessels were sunk. On 1 February 1942, Enigma U-boat traffic became unreadable because of the introduction of a different [[Cryptanalysis of the Enigma#M4 (German Navy 4-rotor Enigma)|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.{{sfn|Lewin|2001|p=210}} 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 [[Archibald Wavell, 1st Earl Wavell|Wavell]] and [[Claude Auchinleck|Auchinleck]] to prevent [[Erwin Rommel|Rommel's]] forces from reaching Cairo in the autumn of 1941.{{sfn|Winterbotham|1974|p=187}}
* Ultra intelligence from Hagelin decrypts, and from {{lang|de|Luftwaffe}} and German naval Enigma decrypts, helped sink about half of the ships supplying the Axis forces in North Africa.{{sfn|Hinsley|1993a}}<ref name=mrSmith/>
* Ultra intelligence from {{lang|de|Abwehr}} transmissions confirmed that Britain's Security Service ([[MI5]]) had captured all of the German agents in Britain, and that the {{lang|de|Abwehr}} still believed in the many [[double agents]] which MI5 controlled under the [[Double Cross System]].{{sfn|Smith|2007|p=129}} This enabled major deception operations.{{sfn|Budiansky|2000|pp=315–316}}
* 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.{{sfn|Lewin|2001|p=237}}
* 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.{{sfn|Jones|1978|p=336}}
* Ultra contributed to [[Bernard Montgomery, 1st Viscount Montgomery of Alamein|Montgomery's]] victory at the [[Battle of Alam el Halfa]] by providing warning of Rommel's planned attack.<ref name=mrSmith>{{cite web |last1=Smith |first1=Kevin D. |url=https://books.google.com/books?id=b1rsIQMC-1QC |title=The contribution of Intelligence at the Battle of Alam Halfa |publisher=[[Military Review]] |pages=74–77 |date=July–August 2002 |quote=Only a few days before the battle, Ultra confirmed that Montgomery's estimate of Rommel's intentions was correct.}}</ref><ref>{{cite book |last1=Harper |first1=Glyn |title=The battle for North Africa: El Alamein and the turning point for World War II |date=2017 |isbn=9780253031433 |page=95|publisher=Indiana University Press }}</ref>
* 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.{{sfn|Winterbotham|1974|pp=187–188}}
* A JN-25 decrypt of 14 April 1943 provided details of Admiral [[Isoroku Yamamoto|Yamamoto's]] forthcoming visit to [[Balalae Island]], and on 18 April, a year to the day following the [[Doolittle Raid]], [[Operation Vengeance|his aircraft was shot down]], killing this man who was regarded as irreplaceable.{{sfn|Budiansky|2000|p=319}}
* Ship position reports in the [[Japanese army and diplomatic codes|Japanese Army’s "2468" water transport code]], decrypted by the SIS starting in July 1943, helped U.S. submarines and aircraft sink two-thirds of the Japanese merchant marine.<ref name=mundy>{{cite book|last=Mundy|first=Liza|title=Code Girls: The Untold Story of the American Women Code Breakers of World War II|publisher=Hachette |location=New York, Boston|date=2017|isbn=978-0-316-35253-6}}</ref>{{rp|pp. 226 ff, 242 ff}}
* 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.{{sfn|Lewin|2001|p=278}}
* The success of the [[Battle of North Cape]], in which {{HMS|Duke of York|17|6}} sank the German battleship {{lang|de|[[German battleship Scharnhorst|Scharnhorst]]}}, was entirely built on prompt deciphering of German naval signals.{{sfn|Lewin|2001|pp=227–230}} <!-- December 1943 -->
* US Army Lieutenant Arthur J. Levenson, who worked on both Enigma and Tunny at Bletchley Park, said in a 1980 interview of intelligence from Tunny:{{Quote|Rommel was appointed Inspector General of the West, and he inspected all the defences along the Normandy beaches and send a very detailed message that I think was 70,000 characters and we decrypted it as a small pamphlet. It was a report of the whole Western defences. How wide the V shaped trenches were to stop tanks, and how much barbed wire. Oh, it was everything and we decrypted it before D-Day.{{sfn|Farley|1980|p=39}} }}
* 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.{{sfn|Lewin|2001|p=292}}{{sfn|Budiansky|2000|p=315}}
* Information that there was a German {{lang|de|[[Panzergrenadier]]}} division in the planned dropping zone for the US [[101st Airborne Division]] in [[Operation Overlord]] led to a change of location.{{sfn|Farley|1980|p=40}}
* Ultra assisted greatly in [[Operation Cobra]].
* Ultra warned of the major German counterattack at Mortain, and allowed the Allies to surround the forces at [[Falaise pocket|Falaise]].<!--"destroy" is a bit strong, & operational & command failures played a part more important than Ultra-->
* 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".{{sfn|Winterbotham|1974|p=180}}
* [[Bomber Harris|Arthur "Bomber" Harris]], officer commanding [[RAF Bomber Command]], was not cleared for Ultra. After the invasion of France, with the resumption of the strategic bombing campaign over Germany, Harris remained wedded to area bombardment. Historian [[Frederick Taylor (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 of making the rubble bounce.{{sfn|Taylor|2005|p=202}}