All of us were permitted to come and go freely and to visit and talk with anyone in any area that interested us. We watched the entire operation and had all the techniques explained in great detail. We were thoroughly briefed on the latest techniques applied to the solution of Enigma and in the operation of the Bombes. We had ample opportunity to take as many notes as we wanted and to watch first hand all operations involved. Furnishings were sparse, a desk with a chair for each of us, a pad of paper and a few pencils. The rooms were a bit cold and uncarpeted and a bit dusty but we soon found out that this was a condition common to all work spaces, including the Director's.
The British codebreakers also did everything they could to make the Americans feel at home, Currier recalled.
During lunch hour on one of the many days at BP, we were introduced to ‘rounders’, a game resembling baseball played with a broomstick and a tennis ball. It was a relatively simple game with few complicated rules; just hit and run and keep running. It was not long before I could hit ‘home runs’ almost at will and soon wore myself out running around the bases. Many of our evenings were spent at the home of one or another of our British colleagues. Food and liquor were both rationed, especially liquor, and it was not easy for them to entertain. Whisky and gin were generally unavailable in the pubs and most people had to be satisfied with sherry.
7
WORKING WITH THE AMERICANS
Two days after the American delegation arrived at Bletchley Park, Admiral John Godfrey, the British Director of Naval Intelligence, authorized a full exchange of Japanese signals intelligence between the Far East Combined Bureau and the US Navy's ‘Cast’ codebreaking and intercept site, on the island of Corregidor in the Philippines. The Cast site was based in an underground tunnel at Monkey Point, so called because of a colony of monkeys that had once inhabited the area.
Lieutenant Jefferson R. Dennis, head of the Cast codebreaking section, spent a week in Singapore setting up the procedures for the routine exchange of all information on Japanese codes, ciphers and intercepts. Dennis wore civilian clothes throughout his mission in order to disguise what was going on. He handed over a ‘pinch’ – a stolen version of the Japanese merchant shipping code; a naval personnel code; a new diplomatic hand cipher called ‘Hagi’; and details of how to tell the various types of Japanese naval unit from their call signs.
But the primary target for both Shaw and Dennis was the Japanese Navy's General Operational Code, known to the Americans as JN25. In return for the material Dennis had brought with him, Shaw gave him ‘a current JN25 book and the indicator and subtractor tables up to 31 January, on all of which the US Navy had no information’.
Eric Nave (second from left, front row), the Australian codebreaker who pioneered the breaking of Japanese codes during the inter-war years, acting as interpreter during a visit by the Japanese Navy to Australia, January 1924. Margaret Nave
John Tiltman (right) with Alistair Denniston, the original head of the Government Code and Cipher School (left), and Professor E. R. P. Vincent, later one of the Japanese naval codebreakers, before the move from Broadway Buildings to Bletchley Park. National Archives, Washington, DC
Members of ‘Captain Ridley's Shooting Party’ arriving at Bletchley Park, the country mansion bought by the head of MI6, Admiral Hugh ‘Quex’ Sinclair, from his own funds as the codebreakers’ wartime home. Barbara Eachus
The GC&CS diplomatic and commercial codebreaking operations at No. 7–9 Berkeley Street, London. National Archives, Washington, DC
The accommodation for the operators of the Far East Combined Bureau at Kranji Royal Naval base, Singapore, 1942. Geoffrey Day
John Tiltman, the British cryptographer who broke many of the Japanese codes, including JN25. National Archives, Washington, DC
A Sikh guard at the Kranji wireless station. Geoffrey Day
The market in the North-West Frontier town of Abbottabad, where British codebreakers monitored Russian radio transmissions in the pre-war years. Dennis Underwood
The British intercept and codebreaking base outside Abbottabad. Dennis Underwood
An American Purple machine designed to decipher messages enciphered by the Japanese Type B diplomatic cipher machine, also known to the Japanese as 97-shiki-oo-bun-inji-ki. National Archives, Washington, DC
Frank Rowlett (back left), who broke the Purple machine, Abe Sinkov (right), who took the Purple secret to Bletchley Park, and William Friedman (seated), the ‘father’ of the U.S. Army codebreaking organization.
Oshima Hiroshi, the Japanese Ambassador to Germany, whose reports from Berlin, sent in the Purple cipher, kept the Allies informed of what was going on inside Germany. Oshima is seen talking to a Wehrmacht general in the foyer of the Hanover Opera House. © Public Record Office, WO208/4702
A cartoon by a Bletchley Park codebreaker depicting the variety of unusual people working there. © Public Record Office, HW3/171
Members of Hut 7 during a Japanese language course. Angus Wilson is pictured third from right, front row, Bentley Bridgewater on the extreme left, and Isobel Sandison fifth from left also front row. Isobel Sandison
A page from a Japanese Navy air-ground codebook, designated 2867.
A rare Bletchley Park decrypt of a JN25c message. Movement reports such as these were the most commonly read JN25 messages. © Public Record Office, HW23/1
Prescott and Currier had taken an ‘almost empty’ JN25 codebook with them to Bletchley Park, perhaps unsurprisingly given that the Japanese had introduced a completely new book only two months earlier. The new book, designated JN25b, was larger than the first. There were also several differences in the way in which the keys were generated. But this had not deterred the British codebreakers. Tiltman's early break into the superenciphered code and the fact that the Far East Combined Bureau had around forty people solely employed on JN25 put them in a distinctly advantageous position.
By May 1940, the original JN25 codebook had been sufficiently rebuilt for simple messages to be translated. This success and a bad mistake by the Japanese ensured that the introduction of the new codebook, JN25b, on 1 December 1940 was nowhere near as bad a blow as it might have been, said one of the naval codebreakers working in Singapore at the time. ‘The Japanese introduced a new codebook but, unfortunately for them, retained in use the current reciphering table and indicator system. These had already been solved in some positions and new code groups were discovered immediately. But for this mistake on the part of the Japanese the form of the book might have taken a matter of months to discover.’
The JN25b book given to Lieutenant Dennis already had 500 of its 33,333 code groups recovered. He was also given 4,000 cipher additive groups and 290 indicator additive groups, all of which were from the old system in use before the codebook changed, which was now known as JN25a.
Although these additive groups were no longer in use, they covered the two-month window given to the codebreakers by the Japanese mistake. They were vitally important for the research into that period which was still producing new JN25b code groups. These in turn allowed sustained recovery of the new additive and further recoveries of other groups from the JN25b codebook.
The British in turn were grateful for another source of JN25 messages to supplement their own intercept sites. They were unable at Singapore to receive any messages by day from the Combined Fleet, based in the Japanese Home Waters, and reception of traffic from the Japanese Mandated Islands in the western Pacific was intermittent. The smaller sites at Hong Kong, Esquimalt, in Canada, and Auckland in New Zealand helped, but the Cast station was in an ideal site for reception of both the Home Waters and the Mandated Islands traffic.
The British were not co-operating just with the Americans. They set up an exchange arrangement with a Dutch codebreaking unit, known as Kamer 14 (Room 14), which was based at the Bandung Technical College, in Java, part of the Dutch East Indies. A retired Royal Navy officer, Commander Burroughs, who was living in Java, was called up and appointed as Liaison O
fficer to Kamer 14. The technical exchange was restricted by London to information on diplomatic ciphers because the Dutch were deemed not to have made enough progress on the military and naval codes and ciphers. There was, however, a limited exchange of decrypts and intelligence on military and naval material, particularly where it had a direct importance for the other side.
Nave was meanwhile diagnosed unfit for service in the tropics and sent back on leave to Australia. Since he was flying via the Dutch East Indies, he travelled in civilian clothes and was issued with a civilian passport describing him as an ‘accountant’. But once there, the doctors refused to let him go back to Singapore and he had to be loaned to the Royal Australian Navy to head up a new Australian codebreaking unit.
Captain F. J. Wylie, the head of the FECB, flew to Australia to discuss the setting-up of the new ‘Special Intelligence Bureau’ and co-operation with the Australian intercept units. There were two RAN intercept sites in operation, at Canberra and Townsville, and a small Royal Australian Air Force site at Darwin. Wylie toured all three sites and held a series of meetings with senior RAN officers, including Commander Jack Newman, the Director of Signals and Communications. He also briefed the Australian Prime Minister Robert Menzies and his Defence and Finance ministers on the British codebreaking operations.
The RAN agreed to provide the British with additional coverage of Japanese Navy, consular and commercial traffic, as well as Russian Navy traffic, which Singapore was now too busy to cover. Wylie agreed that Nave should be allowed to set up the new Australian codebreaking section, conceding that ‘in wartime there are certain advantages in avoiding having all eggs in one basket and, in view of the necessity for Commander Nave to remain in Australia, considerable value should be obtained from a subsidiary organization’. But he insisted that its operations would have to be controlled by Singapore.
Wylie also flew to New Zealand to talk to the small Royal New Zealand Navy unit which had been formed in 1940 and as a result two senior RNZN wireless experts were attached to the Kranji intercept site.
The Australian Army had intercept operators and traffic analysts attached to Allied forces in the Middle East working with the Combined Bureau Middle East, a Bletchley Park offshoot based in the former Egyptian Flora and Fauna Museum at Heliopolis, near Cairo. There was no central signals intelligence organization in Australia itself, but Australian military intelligence had intercepted a number of Japanese messages which it had passed on to a four-man ‘unofficial group’ set up at Sydney University to examine enemy codes and ciphers. The group included Thomas G. Room, Professor of Mathematics, and Dale Trendall, Professor of Greek, a knowledge of mathematics being regarded as evidence of the necessary aptitude to understand codes and ciphers and the ability to master unusual languages an assumed prerequisite for mastering Japanese.
Nave's Special Intelligence Bureau was set up at HMAS Canberra in April 1941 to work on material provided by the RAN wireless operators at Canberra and Townsville, the RAAF intercept section at Darwin and a similarly sized military operation in an attic at the Victoria barracks, Park Orchards in Melbourne. Using GC&CS as a model, Nave began recruiting a small number of RAN officers with knowledge of Japanese and by 12 January 1942 had absorbed all four of the academics of the Sydney University Cypher Section.
The military intelligence people had told me that Military Intelligence Sydney had a small group at the university who were studying Japanese cable messages. This showed most commendable planning by the army and also an excellent spirit on the part of the university staff who gave their time in the interests of the country. I met the gentlemen concerned. All agreed to come to Melbourne and the necessary arrangements were made by the army.
An exchange of information on a number of codes and ciphers was agreed between Shaw and Nave. As part of the exchange deal, Professor Room and one of Nave's RAN codebreakers flew to Singapore to ‘pick up tips’ while a Royal Navy Japanese interpreter, Paymaster Lieutenant-Commander Alan Merry, was sent to Melbourne to act as British Liaison Officer.
The British were still well ahead of the Americans on JN25 at this point and the additional traffic from the Philippines, Australia and New Zealand was helping them speed up the breaking of both additive and code groups. By April 1941, they had recovered 30 per cent of the new additive book, although it is not clear how many more of the code groups had been recovered at this point.
A full agreement on exchange of material was completed in May 1941. The Americans appointed a liaison officer, Commander Jack Creighton, to ensure that the exchange worked smoothly, Shaw recalled. ‘To avoid duplication, a mutual signal was sent every three days, giving date and first three groups of JN25 messages received by each party; both would then send copies of the traffic which the other had not received.’
Hard copies and any correspondence on codebreaking methods were sent by safe-hand bag in the weekly Pan-American Airways ‘Clipper’ between Manila and Singapore, securely stashed away in a strongbox specially built into the hull of all the Pan-American Clippers specifically to carry secret government documents.
Since it was ‘well ahead with JN25 results’, the Far East Combined Bureau was initially the ‘controlling unit’ for the deciphering of the JN25 messages, making the vast majority of the recoveries. An improvised one-time pad system was brought in to allow daily exchange of information. The increased co-operation allowed both stations to surge ahead with their recoveries. The Americans had developed a highly mechanized system of using punch-card tabulating machines to sort the code groups and they soon began to catch up with their British counterparts.
There was also collaboration on Japanese military systems between the British codebreakers and the US Army's ‘Station 6’ intercept site at Fort McKinley, near Manila. Two US Army code-breakers were sent to Singapore, where Peter Marr-Johnson, the chief British Army cryptographer, handed them partial solutions of two Japanese Army codes, and Lieutenant Geoffrey Stevens, the FECB's other military codebreaker, was posted to Washington to liaise with the US Army codebreakers.
By now Joan Sprinks and her fellow Wrens had arrived in Singapore and had been integrated into the watch system in operation at the Kranji intercept site.
Kranji was a very happy ship. We all mixed very happily together, except in the station swimming pool where no mixed bathing was permitted. Our mess and quarters had been built specially for the Civilian Wireless Service Personnel but were reallocated to us. The buildings were on six-foot concrete pillars and six of us were accommodated in each block, each with a well-furnished room, bathroom and small veranda. A Chinese ‘amah’ was provided for each block for cleaning and dhobying. The space under the block was a happy hunting ground for frogs and was presumably to discourage snakes and to keep out the flooding caused by sudden tropical downpours.
The Wrens were divided among the four watches alongside the British servicemen and Malayan naval wireless operators who had been drafted in to bolster the bureau's limited resources. George Gamlin, one of the British Army ‘Special Operators’, or Spec Ops, as they were known, recalled.
The Kranji radio sets were rigged in banks of two, one tuned to the transmitting station, the other to the receiving station. Each operator grew to recognize the ‘fist’ or sending technique of the Japanese operators they were monitoring. If required, they could pick out a particular ‘fist’ from dozens of others. This ability became a valuable asset when Japanese units began changing their transmission frequencies and call signs. When this was reported to Kranji, an intense search of the air waves was undertaken, a gruelling task around the clock, not knowing where or when the lost Japanese Army transmitters would be discovered. Y operators searched through so-called ‘banks’ of frequencies. The operators who would recognize the missing ‘fists’ would hurry from set to set, to listen to any strange Japanese signal. Usually a head shake was the answer. Eventually, an exultant cry of ‘That's him’ would be followed by the search for the other end.
Regardless of w
hich service they were in, the intercept operators all worked Royal Navy watches of four to eight hours on and four to eight hours off. With daytime temperatures inside the concrete watchroom often unbearable, the time off came as a welcome relief, said Joan Sprinks.
Working in the watchroom was the hottest thing I have ever known. You had to be there to believe the heat. We were in a concrete building with no windows, no air-conditioning, constantly manned so that it was never aired, additional heating from the sets and a haze and smell of smoking that could almost be cut with a knife. We went on watch armed with giant flasks of iced ‘ayer lima’ [lime water] and small towels to wrap around our necks to absorb as much as possible of the constant sweat. The tropical heat outside seemed almost cool by comparison.
The female operators were reinforced by a further ten Wrens in July 1941. But the third overseas draft of WRNS wireless intercept operators which was sent to Gibraltar met with disaster, Joan Sprinks recalled. ‘They had sailed on the SS Aguila and had been torpedoed by the U-201 in the waters to the west of the Bay of Biscay, the ship sinking in less than a minute with very few survivors. We could hardly believe it. Some of those girls had been on watch with us at Scarborough. They were all really nice girls and first-class operators.’
The Emperor's Codes Page 10