The Secrets of Station X (26 page)

More than that,
Ultra
had come of age. The new organisation sketched out by Welchman and Travis had taken over from the GC&CS of the inter-war years. The dedication and
enthusiasm
that had characterised the inter-war years remained but the need to work in new ways to cope with the huge scale of wartime codebreaking had been fully embraced.

‘Until Alam Halfa, we had always been hoping for proper recognition of our product,’ said Ralph Bennett of his return to Bletchley Park from Egypt in March 1943. ‘Now the
recognition
was a fact of life and we had to go on deserving it. I had left as one of a group of enthusiastic amateurs. I returned to a professional organisation with standards and an acknowledged reputation to maintain.’

The War Office now saw sense in sending potential
codebreakers
to Bletchley where previously it had felt that it was not getting enough in return for the effort its intercept operators and intelligence analysts were putting in. Members of the Army and the ATS were quartered at Shenley Rd Military Camp, about half a mile from Bletchley Park. Bernard Keefe, who worked on Japanese codes, recalled that the camp was commanded by an infantry officer, Colonel George Fillingham.

The Allies now turned their attention to the invasion of
southern
Europe, for which
Operation Torch
had been a necessary precursor. They began by disguising their intentions using a deception plan worked out by the Double Cross Committee which did not involve a double agent at all, but did rely heavily on the codebreakers being able to confirm that the
Abwehr
had been fooled. The most obvious stepping stone to Italy was Sicily, just a short hop across the Mediterranean from Tunisia. The
problem was to find a way of giving the Germans the
impression
that General Dwight Eisenhower and his British colleague General Harold Alexander had other plans, forcing the Germans to reinforce other areas and weakening the defences in Sicily.

Charles Cholmondley, the RAF representative on the Double Cross Committee, devised
Operation Mincemeat
, a plan centred around the known level of collaboration between the Spanish authorities and the Germans. The idea was to drop the body of a dead ‘British officer’ off the coast of Spain, close enough to ensure it would be washed up on the beach, with the intention of making it look as if it had come from a crashed aircraft. He would be carrying documents indicating that the main thrust of the Allied attack would be somewhere other than Sicily. The Spanish were neutral but their sympathies lay with the Nazis and they would undoubtedly pass these on to the Germans, who would reinforce their garrisons in the suggested targets at the expense of the real one.

Ewen Montagu, the Royal Navy representative, took charge of the operation, acquiring the body of a dead tramp from a London hospital and giving it the identity of Major William Martin, Royal Marines, an official courier. Attached to Martin’s wrist by a chain was a briefcase containing a number of
documents
, including a letter from one senior British general to another discussing planned assaults on Greece and an
unspecified
location in the western Mediterranean, for which Sicily was to be a cover. A further letter from Lord Mountbatten, the Chief of Combined Operations, referred jocularly to sardines, which was rightly thought enough of a hint to make the Germans believe the real attack was going to be on Sardinia.

The members of the Double Cross Committee were highly inventive in their choice of other documents to be planted on the body. Two ‘used’ West End theatre tickets for a few days before the intended launch of the body were in his pocket to show that he must have been travelling by air. A photograph
of Martin’s ‘fiancée’, actually that of a female MI5 clerk, was placed in his wallet. For several weeks, Cholmondley carried two love letters from the ‘fiancée’ around in his pocket to give them the proper crumpled look. There was even an irate letter from Martin’s bank manager.

The body was floated ashore near the southern Spanish town of Huelva from a submarine. The Allies now had to find out if the Germans had swallowed the bait and the only sure way of knowing was from
Ultra
, and in particular from the
Abwehr
Enigma traffic between Madrid and Berlin. Following the death of Dilly Knox, his ISK section had been taken over by Peter Twinn with Mavis Lever still one of its key members. The
Abwehr
officers in Madrid were as anxious to find out Berlin’s ruling on the documents as the codebreakers and the deception planners. ‘We were asked to look out for German reactions and the delighted Double Cross Committee knew as soon as Berlin had decided, following a detailed investigation, that “no further doubts remain regarding the reliability of the captured
documents
”,’ Lever said.

Noel Currer-Briggs was still in Tunisia with 1 Special Intelligence Section, when the
Mincemeat
deception reached its denouement.

When Bletchley decyphered the
Abwehr
intercept confirming the results of the German investigation, which showed that the Germans were totally taken in by the deception, a message was sent to Churchill, then in the US for the Trident Conference with US President Franklin D. Roosevelt, saying simply: ‘
Mincemeat
swallowed whole.’

The ability the Allies now had, through
Ultra
, to tell whether or not the enemy had been fooled by deception operations was another crucial contribution made by the codebreakers to Allied intelligence operations, said Ralph Bennett.

Even two months later, when the invasion of Sicily had been launched, German intelligence continued to insist that the original plan had been to attack Sardinia and Greece and that it had only had been switched to Sicily at the last moment.

T
he Allied landings first in Sicily in July 1943 and then in Italy itself in September, followed swiftly by the Italian surrender, provided
Ultra
with its first strategic test. Hitler’s reaction was uncertain. Would he accept Rommel’s advice and take the
logical
course and retreat to the Alps, saving men and material, or would he fight every inch of the way as proposed by the German commander in Italy, Field Marshal Albert Kesselring? Bletchley Park was able to follow Hitler’s decision-making, as he initially agreed with Rommel and then accepted the
argument
of Kesselring that the Germans must make a stand on successive defence lines all the way up the peninsula. ‘This was the strategic prize of the greatest moment,’ said Ralph Bennett. ‘It enabled the Allies to design the Italian campaign to draw maximum advantage from the willingness Hitler thus displayed to allow Italy to drain away his resources.’

The German ability during the Italian campaign to use long pre-established landline communications limited the ability of Hut 6 to produce useful material from the Enigma decrypts. The breaks into the
Red
continued but while other Enigma keys could be broken intermittently, sometimes in floods, it was more often in a trickle that could not be used to produce reporting of any great substance. One former Hut 6 codebreaker said:

Fortunately, the Bletchley Park codebreakers now had another source of high-grade German intelligence that more than filled the gap in Italy, and ensured they not only knew what Hitler and his generals were thinking but also had a constant and comprehensive guide to all the German dispositions and intentions.

The Germans were using an encyphered radio teleprinter system for communications between Hitler and his senior commanders. The earliest indications of this encyphered radio teleprinter system came in the second half of 1940 when the Metropolitan Police unit at Denmark Hill under Harold Kenworthy picked up unidentified German non-Morse signals. No effort was put into intercepting these transmissions until mid-1941 when an RAF station at Capel-le-Ferne, near Folkestone, picked up similar signals. ‘The transmissions were erratic,’ said Kenworthy. ‘But on one occasion, a secret
teleprinter
message in clear was intercepted reporting the removal of a Flak [
Fliegerabwehrkanone
– anti-aircraft gun] battery to the Eastern Front.’ Denmark Hill was asked to take a closer look at the teleprinter signals with the assistance of the GPO intercept station at St Albans.

The first regular transmissions intercepted by the British were on an experimental
Wehrmacht
link between Vienna and Athens which used the Lorenz SZ40 cypher machine. The
radio-teleprinter
traffic had been mentioned in the Enigma traffic as
Sägefisch
(sawfish), probably because of the teeth on the SZ40’s rotors, and as a result the Bletchley codebreakers gave the
radio-teleprinter
traffic the codename
Fish
, with the SZ40 traffic itself given the codename
Tunny
. Another teleprinter encyphering system, the Siemens and Halske T52
Geheimschreiber
, was also
detected in use by the Germans, mainly by the
Luftwaffe
, and was codenamed
Sturgeon
, but because of the lack of Army Enigma the codebreakers decided to concentrate on the
Tunny
material produced by the Lorenz machine.

This worked on a system invented in America in 1918 by Gilbert Vernam. Teleprinter transmissions are based on the international Baudot system, a binary code in which each letter is made up of a series of five elements, or ‘bits’. Each of these ‘bits’ is either a ‘mark’ – the equivalent of the binary 1 and denoted by a cross – or a ‘space’ – the counterpart of the binary 0 and represented by a dot. Each ‘bit’ is transmitted as a separate negative or positive impulse.

‘The letters were in the form of five elements, always preceded by a start signal and always followed by a stop signal,’ said Ken Halton, one of the GPO teleprinter engineers who worked at Bletchley. ‘So they were basically seven units in length, the middle five being the active code elements. The start signal and the stop signal were there to start and stop the machine at the receiving end.’

The Baudot Code as it is known was not secret, but Vernam’s cypher system combined the five elements for one letter with those of another letter ‘randomly’ selected by a cypher machine to produce a third encyphered letter. Each of the five elements that made up the letter under the Baudot Code were added to each other on the basis that like and like, either two marks or two spaces, would produce a space, while like and unlike, i.e. a mark combined with a space, produced a mark. Once the cypher machine was introduced the new combination of marks and spaces constituted a third, encyphered letter. For example, if the letter A – which in the Baudot Code is represented by ×ו•• – is added to B – which is ו•×× – the result would be •×•×× or the letter G.

The beauty of this system lay in the decyphering process. Since, in binary mathematics, addition is the same as
subtraction
, an identically set cypher machine at the receiving end
had only to add the same pattern of ‘random’ letters to the encyphered letters, or effectively re-encypher the message on the same setting, to come up with the original clear text. The Lorenz SZ40 took Vernam’s idea one stage further, adding not one but two separate ‘random’ letters to the original letter in an attempt to make it even more difficult to decypher.

The Lorenz machine had twelve wheels, ten to encypher the message, paired in two separate rows of five, and two motor wheels. The movement of the wheels was very complex. Each of the encyphering wheels had a number of springed teeth equally spaced around its circumference which could be put into an active or inactive position to form either a mark or a space. The first wheels in each of the pairs, known as the ‘chi’ wheels, moved regularly one position with each letter. The ‘chi’ wheels were geared to move at different speeds and each had a different number of positions it could adopt. The second wheels, known as the ‘psi’ wheels, moved intermittently with their motion controlled by the remaining two wheels – the motor wheels. The five elements of the letter were passed through the first set of five wheels, each element through one wheel, and were either modified or left unaltered depending on the addition principle described above and whether or not the pin at that point was active or inactive. They were then passed through the second set of wheels where a similar process took place.

The intercepted teleprinter messages were sent to Bletchley Park where they were examined by John Tiltman and his research group. Tiltman himself did the initial work, quickly identifying the messages as being encyphered using the Vernam system and began to work on a method of unravelling the messages by hand. Tiltman realised that, because of the way that binary mathematics worked, if two messages were sent using the same setting, and they could be lined up so that the starting points matched, adding them together would eliminate the ‘random’ letters that the Lorenz machine had introduced. What would be left would be a combination of the
letters in the two original messages, still in their original
positions
, as if their two binary values had been added together to form one.

A number of messages sent on the same setting, or as the codebreakers described it ‘in depth’, were recovered. But Tiltman was having difficulty separating the clear texts out. Then a lazy German operator came to his assistance. On 30 August 1941, the operator sent a message 3,976 characters long. When asked to repeat it, he sent it again with the exact same settings.

It should have produced exactly the same message which would have been no help to Tiltman at all. But although the codebreakers knew from the operator chat that the two messages were the same and they certainly began identically, within a few letters they had become different. The vital clue that allowed Tiltman to work out what had happened was the fact that this message had fewer characters. The operator had left something out of the original message.

Anxious to cut down the length of time the job would take, he had abbreviated a number of parts of the message, beginning with its introduction. He had cut the word
Spruchnummer
, message number, using the German abbreviation for number to make it
Spruchnr
. Tiltman now knew that if he lined the subsequent apparently different parts of the two messages up and added them together, it would strip off the keys, leaving him with two identical clear texts added together.

Because each character of the combined text represented only one letter, albeit it added to itself, the stripped text would have similar characteristics to the German language and could be recovered relatively easily by exploiting basic cryptanalytical tools such as letter frequency.

Sadly it was not quite as easy as that because the message had been abbreviated in a number of places. But Tiltman, who preferred to work alone, standing at a custom-built high desk, was a brilliant codebreaker. Gradually he worked his way through the message recovering the clear text up to the next
abbreviation, working out what that was, realigning the two texts and reconstructing the next piece of plain language.

Eventually he managed to recover the complete text. This was in itself an amazing feat. But it was to be followed by one that was perhaps even more remarkable. Once Tiltman had completely decyphered the message all he had to do was add the clear text to the encyphered version to find the elements that had been added by the Lorenz machine. He gave these to the research section so they could try to reconstruct the machine that would have produced those 4,000 letters of key.

‘They worked hard, guided by an ingenious theory, but to no avail,’ recalled Bill Tutte, one of the other members of the research section. He later wondered if it was ‘a gesture of despair’ that led Captain Gerry Morgan, his immediate
superior
, to hand him the key strip and some other documents and say: ‘See what you can do with this.’ Tutte, a young Cambridge chemistry graduate who had subsequently become interested in mathematics, wrote out a stream of the first of the five
individual
‘bits’ or ‘impulses’ that made up each of the
encyphering
characters, looking for some form of pattern. If only one wheel had been used then a repeating pattern would be found in which every repeat matched precisely with the pattern on the wheel. However if two wheels had been used the precise pattern repeated in each row produced by the first wheel would to some degree be altered by the effects of the second wheel in the pair. Tutte detected a pattern suggesting that one of the wheels might be able to produce twenty-three different positions, or possibly twenty-five. So he decided to test both out, multiplying the two together to form 575 and using that as a basis for his work. In doing so he realised that 574 was an even better fit.

It clearly worked. One of the wheels on the machine did have forty-one positions. At this stage of the process, the rest of the section joined in the attack. It later transpired that Tutte’s initial belief that one of the wheels had twenty-three positions was correct, but it was the last of the chi-wheels so it would have taken a lot longer for his attack to succeed, although it would have done so in the end. ‘Then I suppose my success would have been attributed entirely to close logical reasoning,’ Tutte later mused, suggesting that other members of the research section, frustrated in their own efforts, might not have been as generous in their praise as he deserved. ‘As things were, I was supposed to have had a stroke of undeserved luck,’ Tutte wrote. ‘Think twice, O Gentle reader, before thou takest an unexpected and opportune short cut.’

Once Tutte began to make progress, other members of the research section joined in and they managed to work out its complete internal structure and how it operated right down to the intermittent movement of the second row of wheels.

Given that no one at Bletchley had any idea what a Lorenz machine looked like, Tutte had achieved a near miracle, but he remained unassuming and modest about his feat, recalled Shaun Wylie, who later moved from Hut 8 to work on
Tunny
. ‘You could hardly get anything out of him,’ Wylie said. ‘I once wanted to hear from him the saga about how he’d done his astonishing bit of work and I think we got interrupted after about half an hour but I really hadn’t got much out of him.’

But the importance of the breakthrough was not lost on those in charge. ‘That the Research Section was in fact able to achieve this feat within a matter of a few months was one of the outstanding successes of the war,’ said Nigel de Grey. With Tiltman and Tutte having shown that it was possible to break the
Tunny
traffic, it was decided to set up a section to exploit it, de
Grey added. ‘The system was being fairly rapidly extended by the Germans over their high command networks and such messages as could be decyphered by “depth” reading left little doubt that their contents would have considerable intelligence value.’

The new section was run by Ralph Tester and therefore became known as ‘the Testery’. Ralph Tester was a 39-year-old accountant who, having spent much of his working life in Germany, had an exceptionally deep knowledge both of the country itself and the language. He had been working with Tiltman on police cyphers having only recently transferred to Bletchley from the BBC Monitoring Service at Caversham, near Reading, which intercepted German public radio broadcasts. A small site at Knockholt, near Sevenoaks in Kent, which was owned by Section VIII, the radio section of MI6, was used to intercept the
Tunny
material.