The Bletchley Park Codebreakers (20 page)

Harry Hinsley, the leading naval intelligence analyst at Bletchley Park, was sent to Washington in late 1943 in an attempt to improve co-operation with the US Navy. The result was an agreement, in January 1944, to set up a comprehensive exchange circuit between the main stations tackling Japanese Navy material, including Bletchley Park and the Royal Navy site at Anderson, ‘as early as practicable'.

Perhaps the best example of the new spirit of co-operation came in the breaking of Coral, the successor to the Japanese naval attaché machine cipher broken by Foss and Strachey. With the US Navy now bearing the brunt of the attacks on the German U-boat Enigma, Hugh Alexander, the head of the German naval Enigma section Hut 8, began to examine the Coral cipher. Since the permutations effected by its banks of stepping switches were broadly similar to those made by Enigma, many of the processes used were similar. At the end of September 1943, the British began to make real headway and Alexander produced a report, which according to the official US history, ‘marks the birth of the successful attack on the Coral'.

Alexander flew across to America in early 1944 to help in the final attack on Coral. Since Foss, who had broken Coral's predecessor, had
also just arrived in Washington as liaison officer, he may have been involved too in the discussions with Lieutenant-Commander Frank Raven, who had been leading the US Navy team that solved Jade, a different Japanese navy machine. By 11 March, the codebreakers had solved the wiring of the Coral machine and read a few messages. The British codebreakers ‘contributed heavily' to what was a joint US-British success, the US history records. Coral, together with the Japanese military attaché code and the Purple diplomatic cipher, would also contribute to the Allies' knowledge of the German defences in Normandy and thus to the success of the D-Day landings.

As the Allies pushed forward on a number of fronts in the Far East, the codebreakers benefited from an increasing number of ‘pinches' of Japanese codebooks. One of the most important, and certainly the largest, occurred in early 1944 when the 9th Australian Division overran the positions of the 20th Japanese Division at Sio in northern New Guinea. The division's chief signals officer should have burned its codebooks. Instead he dumped them into a water-filled pit inside a metal container. When it was retrieved it was found to contain the current code-books for six different mainline systems, allowing the Allies to read the Japanese military codes for the next two months and to keep on top of most of the main military systems after new code-books were introduced. The Central Bureau was able to provide General Douglas MacArthur, the Allied commander, with full details of the Japanese order of battle in New Guinea, greatly aiding his advance.

Bletchley Park now began to reinforce the Central Bureau with a number of graduates of the Bedford course. Hugh Melinsky, who had been recruited from Christ's College, Cambridge, arrived in April 1944 as one of a dozen or more British reinforcements. He was put to work on the naval air desk, part of Eric Nave's air-ground section. ‘What Captain Nave did not know about code-breaking was not worth knowing,' Melinsky said. ‘He had a sixth sense which enabled him to sniff out a meaning in what looked to me like a jumble of letters or numbers.' Melinsky and other British codebreakers were sent forward with Australian mobile wireless units to provide MacArthur with up-to-date tactical intelligence as the Allies pushed northwards.

The British and Indian advances in Burma during the second half of 1944 and into 1945 were also aided by mobile signals intelligence units that pushed forward with the Allied troops. But one of the most
significant pieces of assistance they received from Sigint was a result of Bletchley Park's breaking of the three-figure super-enciphered code used by the Japanese Army Air Force for its communications with the ground, known as
kuuchi renraku kanji-hyoo 2-goo
to the Japanese and BULBUL to the Allies. The code was broken in the new Japanese air section, which was rapidly expanding, with around 250 people working on army air alone in September 1944, but was exploited in India to great effect.

Michael Kerry was one of the codebreakers assigned to work on the BULBUL code in Comilla. ‘The Japanese bombers used to be kept safely down in Bangkok and then when there was a full moon, they were moved forward to the Mingaladon air base in Rangoon. On one occasion we got wind in advance that a raid was going to take place and passed the information on. Most of the time, we had no way of knowing if what we did was a pennyworth of use but in this particular instance the nightfighters got the lot and all night we could hear Mingaladon air base calling for its lost children.'

The US codebreakers' achievement in breaking the Purple cipher, and the fact that they were reading the main Japanese Navy code JN-25, was revealed almost immediately the war ended through a series of leaks and the congressional inquiry into the attack on Pearl Harbor. But the part played by the British codebreakers in the war in the Far East remained secret until the late 1990s when GCHQ began to release the files that recorded the achievements of men like Tiltman, Foss and Nave. As a result, most of the existing literature credits the Americans with having led the way in the breaking of the Japanese codes and ciphers. Only now are the British codebreakers beginning to receive the recognition they deserve.

9

SOLVING JN-25 AT BLETCHLEY PARK: 1943–5

EDWARD SIMPSON

When Italy surrendered in August 1943 I was a mathematician cryptanalyst TJAO (Temporary Junior Administrative Officer) in Italian Naval Section, in Block B, which was headed by Wilfred Bodsworth (‘Boddy'). He in turn reported to Frank Birch, Head of Naval Section.

Mostly I worked on the main Italian Naval subtractor
Cifrario Libia
. It was not being read currently, so there was less sense of urgency than elsewhere. By contrast, for the first few days of each month I joined the Italian Naval Hagelin team under Colin Thompson (later Director of the National Galleries of Scotland). The Hagelin C-38 cipher was read currently and was of major importance for the harrying of Axis shipping carrying supplies to North Africa. Its keys changed monthly and the team then borrowed additional mathematicians. We worked intensively on three shifts until the new month's keys were broken.

Elsewhere in Italian Naval there were many small ciphers on the go as well as the big ones. One simply used the Calendar of Saints
for a daily key; we called it the Holy Indicator. We all looked over each others' shoulders a lot and chipped in with comments and suggestions. Boddy's management style was that of the senior member of a common room rather than that of a director.

So when I was made TSAO (Temporary Senior Administrative Officer) and told to head the new team on the cryptanalysis of JN-25, this was a novel concept. Having gone to Bletchley Park in October 1942, directly after graduating at age 19, I had neither managed nor been managed. I now reported to Commander J. P. McIntyre RN, a Japanese linguist with experience of JN-25 in Singapore.

Those who moved from Italian to JN-25 with me were mainly the younger ones. The aristocrats and the senior academics (June Capel, Elizabeth Wyndham, Philip Hall of King's and later Sadleirian Professor at Cambridge, Professor (of Classics) T.B.L. Webster and his equally Hellenic wife Margery Dale, Patrick Wilkinson of King's, Cambridge, and his wife-to-be Sydney Eason, Professor (of Italian) E. R. Vincent, Professor (of German) Walter Bruford who had worked in Room 40, Willy King (from Ceramics at the British Museum) all dispersed elsewhere.

Of our group, Tony (A. J.) Phelps (an Oxford classicist) and Gladys Gibson (an English graduate and now my wife Rebecca Simpson) and I immediately went on John Lloyd's first short Japanese Language Course within the Park for the month of September. Mathematicians who joined me were Ian (J. W. S.) Cassels, later Fellow of Trinity and Sadleirian Professor at Cambridge, and Jimmy (J. V.) Whitworth. Both were newcomers to Bletchley Park. Also from elsewhere came Lieutenant-Commander Belfield RN, grey-haired and courteous but without any known Christian name, who had intelligence experience in the 1914–18 war and had worked on Italian ciphers in Alexandria in this one.

At the beginning of October our team numbered 20. The four men TJAOs had a total – not an average – cryptanalytical experience of 23 months. Of the more junior staff, all civilians, I can name: José Cassar, Gill Cave, Adelaide Dickens, David Foxon, Mary Fraser, June Jarratt, Christine Kendall, Jimmy Love, Mary Manners, Margaret Pyke, Frances Sidebotham, Olive Thorogood, Joyce White, Petronella Wise. They varied in rank from unskilled Grade III to junior cryptographer TA and in experience from three months to four years. Ability to do the JN-25 job was not well correlated with rank and experience; a
problem which was exacerbated with the arrival later of Wrens whose quickness more than compensated for their inexperience.

We acquired a third Japanese linguist at the end of March 1944: following the Italian surrender Henry Reed had gone from Italian Naval to the six-month language course. After a year in our party he took over the direction of the one-month course. Although he was older than most of us – all of thirty – and in poor health, Henry was not exempt from serving in the Bletchley Park Company of the Home Guard. He was not a very military person but his Home Guard service has left us a memorable experience. His poems ‘The Naming of Parts', described as ‘the best-loved and most anthologised poem of the Second World War', and ‘Judging Distances' beautifully and laconically balance the unforgettable teaching style of our two regular Army Sergeant-Instructors with what caught his eye when his attention wandered.
*

For six months from January to July 1944 Japanese Naval was joined by Marshall Hall, already a noted academic mathematician at Yale, and thinly disguised as a Lieutenant, US Navy. He was for that period OP-20-G's Liaison Officer on Japanese matters. He was not attached to any one party but moved around them all, including ours, discussing and advising in a very wry and acceptable way. He introduced to us ‘Hall's Weights', a statistical approach which I describe (but inadequately) in Appendix VII.

Two Lieutenants of the Royal Canadian Navy were posted to our party: Alan Roffey and Wally Fraser. They joined seamlessly both in the work and in off-duty visits that a number of us made together by train and bicycle to the Shakespeare Memorial Theatre at Stratford-upon-Avon whose building was then quite new.

We did not move geographically but remained where we had been in Italian Naval on the upper floor of Block B. The internal partitions have all gone but it is easy to reconstruct them. There is a staircase at the East end of the Block, directly overlooking Block C: the mathematicians had the room at the head of it. Next to it a very small room which Commander Belfield, in recognition of his seniority, had to himself. Next, on the side of the central corridor facing the lake, was our headquarters room occupied by myself with our Japanese linguists and Olive Thorogood who worked with them in producing in-team intelligence: this group took the name GEN.
Across the corridor in the Big Room, Adelaide Dickens had day-to-day charge of the main additive recovery work, ranging from servicing the paperwork to the cryptanalysis itself.

In passing, the room next to our headquarters was occupied by two Army Intelligence Captains who ran JN-11, the system in use by the Japanese Auxiliary Fleet. One of them, Brian Augarde, a professional jazz clarinettist, created the BP Jazz Quintet which contributed joyfully to the Park's rich musical life but is usually overlooked by those who write about the classical music performances and operas. The range and celebrity quality of these was astonishing, as has often been observed. They took place in the Assembly Hall which had been built outside the perimeter fence so that the people of Bletchley could use it too.

In July 1943 a performance of ‘Acis and Galatea' produced within the Park had Peter Pears and Elizabeth Welch as visiting singers in the title roles. Myra Hess gave a recital in November. These were followed by Denis Matthews, the Jacques String Orchestra, Isobel Baillie, Leon Goossens, Maggie Teyte, Francis Poulenc and Pierre Bernac. The Ballet Rambert were dancing on 7 May 1945 as Germany surrendered. We had equally distinguished lectures: three talks in September 1943 on invasions of Sicily from the Normans through Garibaldi (the Allies had landed there in July); the Marquess of Linlithgow, former Viceroy, on India; Arthur Bryant; Emil Cammaerts (whose daughter Jeanne was in the Park and son Francis was among the most distinguished of the Special Operations Executive) on Rubens. These are occasions that I attended; it does not pretend to be a complete list.

Unmentioned elsewhere, to my knowledge, is a special occasion in the cinema which also operated in the Assembly Hall. In April 1945 it showed
Münchhausen
, in Agfacolor with German soundtrack and no subtitles: this had been released in Germany in March 1943. It was shortly followed by a showing of the less distinguished
Die Goldene Stadt
(1942). There must be a good story as to how these came to be shown at Bletchley Park, but I do not remember any comment on this at the time.

Encoding and enciphering by JN-25 is described in Appendix V. Very briefly, the message text was first transformed into a series of 5-digit codegroups. These were then disguised by adding to each, using non-carrying addition, 5-digit ‘additives' taken consecutively from a table of many pages, with ten rows and ten columns of additives on each page. An ‘indicator' system showed where to start.
The cryptanalysis of JN-25 was no different in principle from that of the Italian
Libia
with which we were familiar. True, the code-groups had five digits instead of four, they ‘scanned' (as a garble check, the sum of the five digits was divisible by three in virtually all the JN-25 codes) and the language was totally foreign whereas Italian had never seemed forbidding even to those who had not studied it. But we were taking aboard variations, not starting something new.

The JN-25 ‘traffic' – the intercepted messages – was by now divided into four channels sharing the same codebook but each with its own additive table and indicators. The Channel labelled A, which was used by nearly all vessels for important routine communications, had about 300 messages daily. The B Channel was used by most vessels, except submarines, for strategic communications and had about a quarter of that number: enough in each case to make the cipher readable. Two other channels had too little traffic to approach readibility. It did not take us long to decide that the A Channel was too big for us and that we would concentrate on the B Channel. As each new codebook came into use it was given a capital letter designation, and each new additive table an Arabic numeral. For example, the B Channel system in force when we started was J-24.

Allied cryptanalysts had been working on JN-25 for a long time so we had at our disposal at once a substantial body of established ‘good groups': groups known to be in the codebook because they had appeared in bits of message text previously deciphered. Far from starting from scratch, we were straight into the systematic recovery of new additives. At first we regarded ourselves as experimenting and learning, but by 6 October we felt ready to tell Washington we had been filling in gaps and had recovered over 250 additives: would they like them? When they replied ‘please', we were officially in business.

On 16 October Table 30 came into use in the B Channel; it was not known whether the codebook had changed too. We attacked the traffic using the J codebook anyway, and on 12 November, before any additives had been published elsewhere, we signalled seven additives and the conclusion that codebook J was still in use. Washington agreed that they ‘looked good'. On 6 November we had a visit from Commander Howard T. Engstrom, US Navy, who saw what we were doing and hazarded that, as we grew, there might have to be a partition of work between us and the American stations. With these two encouragements we ended November with high hopes.