Ultra (sometimes capitalised ULTRA) was the name used by the British for intelligence resulting from decryption of encrypted German radio communications in World War II. The term eventually became the standard designation in both Britain and the United States for all intelligence from high-level cryptanalytic sources. The name arose because the code-breaking success was considered more important than the highest security classification available at the time (Most Secret) and so was regarded as being Ultra secret.
Much of the German cipher traffic was encrypted on the Enigma machine, hence the term "Ultra" has often been used almost synonymously with "Enigma decrypts". However, in terms of the intelligence value, Lorenz SZ 40/42 decrypts were more important.
Until the name "Ultra" was adopted, there were several cryptonyms for intelligence from this source, including Boniface. For some time thereafter, "Ultra" was used only for intelligence from this channel.
Group Captain F.W. Winterbotham, in The Ultra Secret (1974), quotes the western Supreme Allied Commander, Dwight D. Eisenhower, as at war's end describing Ultra as having been "decisive" to Allied victory in World War II. Eisenhower is also reported to have said that Ultra may have shortened the war by as much as two years.
ULTRA intelligence was largely derived from German cipher traffic. These messages were mostly generated on several variants of an electro-mechanical rotor machine called "Enigma." The Enigma machine was widely thought to be in practice unbreakable in the 1920s, when a variant of the commercial Model D was first used by the German Navy. The German Army, Navy, Air Force, Nazi party, Gestapo, and German diplomats all used Enigma machines, but there were several variants (e.g., the Abwehr used a four-rotor machine without a plugboard, and Naval Enigma used different key management from that of the Army or Air Force, making its traffic far more difficult to cryptanalyse). Each variant required different cryptanalytic treatment. The commercial versions were not as secure. Dilly Knox, of GC&CS, is said to have broken it during the 1920s.
Later in the war, in 1941, the Germans introduced on-line stream cipher teleprinter systems for strategic point-to-point radio links, to which the British gave the generic code-name FISH. Several distinct systems were used, principally the Lorenz SZ 40/42 (initially code-named TUNNY) and Geheimfernschreiber (code-named STURGEON). These cipher systems were also successfully cryptanalysed, particularly TUNNY, which the British thoroughly penetrated. It was eventually attacked using the Colossus computers, which were the first digital program-controlled electronic computers. Although the volume of intelligence derived from this system was much smaller than that from Enigma, its importance was high because it produced primarily strategic level intelligence.
In addition to Enigma and Fish decryptions, ULTRA intelligence was supplemented with material derived from radio communications using other methods, such as radio traffic analysis and direction finding.
After the War interrogation of German cryptographic personnel led to the conclusion that German cryptanalysts understood that cryptanalytic attacks against Enigma were possible but they required immense effort and investment.
In the Pacific theater, the Japanese cipher machine dubbed "Purple" by the Americans, and unrelated to the Enigmas, was used for highest-level Japanese diplomatic traffic. It was also cracked by the US Army's Signal Intelligence Service and disseminated under the codeword MAGIC.
Some Purple decrypts proved useful elsewhere, for instance detailed reports by Japan's ambassador to Germany which were encrypted on the Purple machine. These reports included reviews of German strategy and intentions, reports on direct inspections (in one case, of Normandy beach defenses) by the ambassador, and reports of long interviews with Hitler.
The Japanese are said to have obtained an Enigma machine as early as 1937, although it is debated whether they were given it by their German ally or bought a commercial version which, except for plugboard and actual rotor wirings, was essentially the German Army / Air Force machine.
Initially, Army and Air Force related intelligence derived from SIGINT sources (mainly Enigma decrypts) was compiled in summaries at GCHQ (Bletchley Park) Hut 3. The summaries were subsequently distributed under the codeword "BONIFACE", presumably to imply that they were the result of human intelligence operations. The Admiralty (Royal Navy) produced its own intelligence summaries at the RN Operational Intelligence Centre (OIC), which were distributed under the codeword "HYDRO".
In June 1941 new arrangements were made for distribution of Boniface bulletins and from this point on the term "ULTRA SECRET" was used". The term "Ultra" was reportedly suggested by Commander Geoffrey Colpoys, RN, who served in the RN OIC.
The distribution of Ultra information to Allied commanders and units in the field involved considerable risk of discovery by the Germans, and great care was taken to control both the information and knowledge of how it was obtained. Liaison officers were appointed for each field command to manage and control dissemination.
Dissemination of Ultra intelligence to field commanders was achieved by the MI6, which operated Special Liaison Units (SLU) attached to major army and air force commands. The activity was organized and supervised on behalf of MI6 by Group Captain Frederick William Winterbotham. The SLU included intelligence, communications and cryptographic elements. Each SLU was headed by a British Army officer, usually a major, known as "Special Liaison Officer". The main function of the Liaison Officer or his deputy was to pass Ultra intelligence bulletins to the commander of the command he was attached to, or to other indoctrinated staff officers. In order to safeguard Ultra, special precautions were taken. The standard procedure was for the Liaison Officer to present the intelligence summary to the recipient, stay with him while he studied it and then take it back and destroy it.
Fixed SLU's existed at the Admiralty, the War Office, the Air Ministry and RAF Fighter Command. These units had permanent teleprinter links to Bletchley Park.
Mobile SLUs were attached to field Army and Air Force headquarters. These SLUs depended on radio communications to receive intelligence summaries.
The first mobile SLUs appeared during the French campaign of 1940. An SLU supported the British Expeditionary Force (BEF) headed by General Lord Gort. The first liaison officers were Robert Gore-Browne and Humphrey Plowden. A second SLU of the 1940 period was attached to the RAF Advanced Air Striking Force at Meaux commanded by Air Vice-Marshal P H Lyon Playfair. This SLU was commanded by Squadron Leader F.W. (Tubby) Long.
In 1940 special arrangements were made within the British intelligence services for handling BONIFACE and later Ultra intelligence. The Security Service started "Special Research Unit B1(b)" under Herbert Hart. In the SIS this intelligence was handled by "Section V" based at St. Albans.
The communications system was founded by Brigadier Sir Richard Gambier-Parry, who was Head of MI6 Section VIII from 1938 to 1946 and was based at Whaddon Hall in Buckinghamshire, UK.. Ultra summaries from Bletchley Park were sent over landline to the radio transmitter site of Section VIII at Windy Ridge. From there they were transmitted over radio to the destination SLU.
The communications element of each SLU was called "Special Communications Unit" or SCU. Radio transmitters were constructed at Waddon Hall workshops, while receivers were the National HRO, made in the USA. The SCU's were highly mobile and the first such units used civilian Packard cars. The following SCUs are listed: SCU1 (Whaddon Hall), SCU2 (France before 1940, India), SCU3 (Hanslope Park) SCU5, SCU6 (possibly Algiers and Italy), SCU7 (training unit in the UK), SCU8 (Europe after D-day), SCU9 (Europe after D-day), SCU11 (Palestine and India), SCU12 (India), SCU13 and SCU14.
The RN Ultra messages from the RN OIC to ships at sea were necessarily transmitted over normal naval radio circuits and were protected by one time pad encryption.
An intriguing question concerns alleged use of Ultra information by the "Lucy" spy ring. This was an extremely well informed, and rapidly responsive, ring which was able to get information "directly from the German General Staff Headquarters"—often on specific request. It has been alleged "Lucy" was, in major part, a way for the British to feed Ultra intelligence to the Soviets in a way that made it appear to have come from highly-placed espionage and not from cryptanalysis of German radio traffic; this is in some doubt, because the Soviets (via an agent in Bletchley, John Cairncross) knew Britain had broken Enigma. The Lucy Ring was operated, apparently, by one man, Rudolf Roessler, and was initially treated with considerable suspicion by the Soviets. The information it provided was accurate and timely, and Soviet agents in Switzerland (including Alexander Rado, the director) eventually took it quite seriously.
The Allies were seriously concerned with the prospect of the Axis command finding out that they had broken into the Enigma traffic. The British were, it is said, more disciplined about such measures than the Americans, and this difference was a source of friction between them.
Ultra information was used to attack and sink many Afrika Korps supply ships bound for North Africa; but, as in the North Atlantic, every time such information was used, an "innocent" explanation had to be provided: often scout planes were sent on otherwise unnecessary missions, to ensure they were spotted by the Germans.
In one particular case, the Germans became suspicious of Ultra when five ships from Naples headed for North Africa with essential supplies for Rommel's campaign were all mysteriously attacked and sunk by an Allied airforce. As there was no time to have the ships all spotted by the airforce beforehand and then sunk accordingly, the decision went directly to Churchill whether or not to act solely on Ultra intelligence. Churchill approved the attack, but afterwards a message was sent by the Allies to Naples congratulating a fictitious spy and informing him of his bonus. According to some sources the Germans decrypted this message and believed it.
In the Battle of Atlantic the precautions were taken to the extreme. In most cases where the Allies knew from intercepts the locations of U-boats in mid-Atlantic, the U-boats were not hunted immediately, until a "cover story" could be arranged. For example a search plane might be "fortunate enough" to sight the U-boat, thus explaining the Allied attack.
Some Germans had suspicions that all was not right with Enigma. Karl Dönitz received reports of "impossible" encounters between U-boats and enemy vessels which made him suspect some compromise of his communications. In one instance, three U-boats met at a tiny island in the Caribbean, and a British destroyer promptly showed up. They all escaped and reported what had happened. Dönitz immediately asked for a review of Enigma's security. The analysis suggested that the signals problem, if there was one, was not due to the Enigma itself. Dönitz had the settings book changed anyway, blacking out Bletchley Park for a period. However, the evidence was never enough to truly convince him that Naval Enigma was being read by the Allies. The more so, since his counterintelligence B-Dienst group, who had partially broken Royal Navy traffic (including its convoy codes early in the war), supplied enough information to support the idea that the Allies were unable to read Naval Enigma.
Of course, in other cases Ultra intelligence could be taken advantage of with little or no risk of a compromise. One example was the military deception preparations for the D-day landings. These involved use of dummy tanks, fake ships and notional armies to fool the Germans into thinking that the Allied invasion would take place at the Pas de Calais, as opposed to Normandy. Ultra intelligence confirmed to the Allies that these deceptions were working, giving all decision makers involved greater confidence of a successful invasion.
By 1945 almost all German Enigma traffic (Wehrmacht, Kriegsmarine, Luftwaffe, Abwehr, SD, etc.) could be decrypted within a day or two, yet the Germans remained confident of its security. Had they been better informed, they could have changed systems, forcing Allied cryptanalysts to start over.
While it is obvious why Britain and the United States went to considerable pains to keep Ultra a secret until the end of the war, it has been a matter of some conjecture why Ultra was kept officially secret for 29 years thereafter, until 1974. During that period the important contributions to the war effort of a great many people remained unknown, and they were unable to share in the glory of what is likely one of the chief reasons the Allies won the war—or, at least, as quickly as they did.
At least three versions exist as to why Ultra was kept secret so long. Each has plausibility. All may be true. First, as David Kahn pointed out in his 1974 New York Times review of F.W. Winterbotham's The Ultra Secret, after World War II the British gathered up all the Enigma machines they could find and sold them to Third World countries, confident that they could continue reading the messages of the machines' new owners. A second explanation relates to a misadventure of Winston Churchill's between the World Wars, when he publicly disclosed information obtained by decrypting Russian secret communications; this had prompted the Russians to change their cryptography, leading to a cryptological blackout. The third explanation is given by Winterbotham (The Ultra Secret, introduction), who recounts that two weeks after V-E Day Churchill requested that former recipients of Ultra intelligence be asked not to divulge the source or the information they had received from it, in order that there might be neither damage to the future operations of the Secret Service nor any cause for the Allies' enemies to blame it for their defeat.
Since it was British and, later, American message-breaking which had been the most extensive, this meant that the importance of Enigma decrypts to the prosecution of the war remained unknown. Discussion by either the Polish or the French of Enigma breaks carried out early in the war would have been uninformed regarding breaks carried out during the balance of the war. Nevertheless it was the public disclosure of Enigma decryption, in the book Enigma (1973) by French Intelligence officer Gustave Bertrand, that generated pressure to discuss the rest of the Enigma/Ultra story.
The British ban was finally lifted in 1974, the year that a key participant on the distribution side of the Ultra project, F.W. Winterbotham, published The Ultra Secret.
The official history of British intelligence in World War II was published in five volumes from 1979 to 1988. It was chiefly edited by Harry Hinsley, with one volume by Michael Howard. There is also a one-volume collection of reminiscences by Ultra veterans, Codebreakers (1993), edited by Hinsley and Alan Stripp.
As mentioned, after the war, surplus Enigmas and Enigma-like machines were sold to many countries around the world, which remained convinced of the security of the remarkable cipher machines. Their traffic was not so secure as they believed, however, which is of course one reason the British and Americans made the machines available. Switzerland even developed its own version of the Enigma, the NEMA, and used it for decades (at least into the late '70s).
Some information about Enigma decryption did get out earlier, however. In 1967 the Polish military historian Władysław Kozaczuk in his book Bitwa o tajemnice (Battle for Secrets) first revealed that the German Enigma had been broken by Polish cryptanalysts before World War II. The same year, David Kahn in The Codebreakers described the 1945 capture of a Naval Enigma machine from U-505 and mentioned, somewhat in passing, that Enigma messages were already being read by that time, requiring "machines that filled several buildings." In 1971 Ladislas Farago's The Game of the Foxes gave an early published version of the myth of the purloined Enigma that enabled the British (according to Farago, Alfred Dillwyn Knox) to crack the cipher (Farago also mentions an Abwehr Enigma). By 1970 newer, computer-based ciphers were becoming popular as the world increasingly turned to computerised communications, and the usefulness of Enigma copies (and rotor machines generally) rapidly decreased. It was shortly after this (1974) that a decision was taken to permit some revelations about some Bletchley Park operations.
Wintebotham summarizes the wartime consequences in the last chapter of his book.
In May 1940 the Allies failed to take advantage of Ultra in France, especially the French, although Ultra intelligence helped organize evacuation of the British Expeditionary Force (BEF).
In the summer of 1940, British cryptanalysts, who were successfully breaking German Air Force Enigma-cypher variants, were able to give Churchill information about the issuing of maps of England and Ireland to the Sealion invasion forces. Ultra also revealed to the British that the threat of invasion was over, when on September 17 Hitler authorized the dismantling of aircraft loading ramps at Dutch airfields.
Breaking of some messages (not in German Enigma) led to the defeat of the Italian Navy at Cape Matapan, and was preceded by another "fortuitous" search-plane sighting. British Admiral Cunningham also did some fancy footwork at a hotel in Egypt to prevent Axis agents from taking note of his movements and deducing that a major operation was planned.
Ultra intelligence was of considerable assistance to the British (Montgomery being "in the know" about Ultra) at El Alamein in Western Egypt in the long-running battle with the Afrika Korps under Rommel.
Intelligence from signals between Adolf Hitler and General Günther von Kluge was of considerable help during the campaign in France just after the Allied D-Day landings, particularly in regard to estimates of when German reserves might be committed to battle.
On the other hand, the Red Army was well aware of the German buildup, locations and attack time precisely, prior to the battle of Kursk even without the Ultra information provided to them. However, there is some evidence to suggest that the Lucy spy ring of Switzerland, which provided crucial information about Stalingrad and Kursk, was in truth a method of passing Ultra information to Moscow without detection by the Germans.
It is commonly claimed that the breaks into Naval Enigma resulted in the war being a year shorter, but given its effects on the Second Battle of the Atlantic alone, that might be an underestimate.
An exhibit in 2003 on "Secret War" at the Imperial War Museum, in London, quoted British Prime Minister Winston Churchill telling King George VI, "It was thanks to Ultra that we won the war." Churchill's greatest fear, even after Hitler had suspended Operation Sealion and invaded the Soviet Union, was that the German submarine wolf packs would succeed in strangling sea-locked Britain. He would later write, in Their Finest Hour (1949), "The only thing that ever really frightened me during the war was the U-boat peril." A major factor that averted Britain's defeat in the Battle of the Atlantic was her regained mastery of Naval Enigma decryption.
There were, however, also other technologies, equipments, and tactics which moved the Battle of the Atlantic in the Allies' favour. As the air gap over the North Atlantic closed and convoys received escort carrier protection, anti-submarine aircraft became extremely efficient hunter-killers with the use of centimetric radar and airborne depth charges. Improvements to Huff-Duff (radio triangulation equipment used as part of ELINT) meant a U-boat's location could be found even if the messages they were sending could not be read (and simply avoiding a known submarine was often sufficient). Improvements to ASDIC (SONAR), coupled with Hedgehog, improved the likelihood of sinking a U-boat.
From February 1942, when Air Marshal Arthur Harris became Air Officer Commanding of Bomber Command, the RAF implemented large-scale night area bombardment of German cities. The destruction of city centres not only killed civilians and destroyed factories, houses and railways, but damaged and degraded the telephone and telex network. The long-distance cable network would usually be quickly repaired, and the telex network was closed down by the Allies only on May 8, 1945. However, as the war progressed, a surge in communications demand by German command-and-control, and the effect of unrepaired destruction, forced the Germans to rely ever more heavily on encrypted radio traffic, which the Allies were able to read.
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 of "making the rubble bounce" in every large German city.
F.W. Winterbotham, the first author to outline, in his 1974 book The Ultra Secret, the influence of Enigma decryption on the course of World War II, likewise made the earliest contribution to an appreciation of Ultra's postwar influence, which now continues into the 21st century—and not only in the postwar establishment of Britain's GCHQ (Government Communication Headquarters) and the United States' NSA (National Security Agency). "Let no one be fooled," Winterbotham admonishes in chapter 3, "by the spate of television films and propaganda which has made the war seem like some great triumphant epic. It was, in fact, a very narrow shave, and the reader may like to ponder [...] whether [...] we might have won [without] Ultra."