The Emperor's Codes

by Michael Smith

  Partly in order to improve security, a Special Liaison Unit (SLU) was set up in Delhi in early 1944 to pass the intelligence gathered by the codebreakers on to Slim. The SLUs had first emerged during the Battle for France in 1940 and were designed to provide Ultra intelligence swiftly and securely to commanders in the field. They were made up of communications experts to link the unit to the codebreaking centres plus intelligence officers provided by MI6, who passed the Ultra material on to the commanders. Their role was to control the use of high-grade signals intelligence strictly to ensure that only those who had been indoctrinated knew of its existence. They also had to enforce the regulations on its use, making sure that it was never acted upon without a secondary source being available, and to liaise with the codebreakers on any queries from commanders. Two other SLUs were set up, one at Comilla to pass the signals intelligence to Slim and the other at Mountbatten's headquarters in Peradeniya four miles west of Kandy.

  Frederick Winterbotham, the MI6 officer in charge of the SLUs, flew to Comilla to discuss the arrangements with Slim himself.

  General Slim's HQ was in a large old Indian house, its spacious grounds covered with scented shrubs and shady trees and a small tented camp in a sunken garden. Beneath the house lived father, mother and three baby mongoose who kept the snakes away both from the house and our tents, which was a comforting thought.

  The type of Ultra information received from the Japanese was much the same as that received from the German Army in Europe, operational and movement orders, strength returns and locations of Japanese formations which not only formed useful targets for the air but gave General Slim a complete order of battle of the Japanese forces.

  Ken Kelsey was posted to the Kandy SLU in mid-1944 as a twenty-one-year-old RAF sergeant cipher operator.

  Mountbatten's HQ was situated in the Botanical Gardens in Peradeniya. Its proud boast was that it contained a specimen of every species of tree in the world. Whether this is true or not I do not know, but it was a wonderful environment in which to work.

  All the SLU personnel were RAF and technically responsible to air intelligence in Whitehall. This gave us certain privileges – we could not be put on a charge; we were excused all fatigue and guard duties and the like; and it was our duty to avoid capture. We had two means of receiving signals, a teleprinter link from Colombo and a radio link from our Special Communications Unit receiving signals from the Wireless Experimental Centre in Delhi, which was essentially Bletchley Park overseas. It would come in Type X cipher in five-letter groups and we would decipher it on a strip of plain-language text which would then go to Mountbatten.

  The shifts were very, very onerous. We worked eight hours on, then sixteen hours off, followed by sixteen hours on and eight hours off, and when you went off to sleep you had these five-letter groups going through your mind all the time. We tried to swap shifts between ourselves to get a full twenty-four hours off occasionally but then you just had to work longer shifts when you came back.

  Our living quarters were in a rubber plantation two or three miles away. Wherever I went in the Far East the toilet arrangements were uniformly abysmal. Snakes used to collect in the pit beneath our thunderboxes, and we were advised to take a razor blade with us in case we were bitten. We were then supposed to ask a fellow squatter to take the blade, slice open the bite and suck the venom out! You can imagine the ribald comments which greeted this advice. However, Lord Louis's loo at the HQ was immaculate. It possessed a flush toilet, decent toilet paper, a mirror, a strip light and a shelf on which were perfumes and lotions. I used to like the night shift, for at around 3 a.m. when there was never a soul about I would slip across to his quarters and avail myself of all the facilities. You can have no idea of the extent to which my morale was lifted by these few but precious visits.

  As the 14th Army prepared for its thrust through central Burma, the codebreakers warned that the Japanese had reinforced their troops in the region with four divisions and appeared to be preparing an attack of their own. On 6 March the Japanese 15th Army crossed the Chindwin River on a broad front heading for the two small towns of Kohima and Imphal, centres for Assam's tea industry before the war but now home to the British frontline garrisons. Inspired by Slim's leadership, and sustained by occasional airlifts, the British and Indian troops stood firm through eighty days of siege and some of the bitterest fighting on any front of the war.

  Slim's determination that his men should not to yield to the Japanese was built on the detailed knowledge of the Japanese position that was being fed to him by the codebreakers. Winterbotham recalled:

  Some of the most interesting signals had been those showing the shortages of rations and equipment. General Slim told me that the intelligence from Ultra about the Japanese forces had been invaluable throughout the campaign, but the real triumph had been the information which led up to the final attack by the Japanese at Imphal and Kohima. It had become very evident from Ultra that the Japanese supply position was desperate and that their attack was being planned in order to capture the 14th Army supply depots, so as to keep the Japanese Army in business. Ultra had also shown that the Japanese Air Force in the area had dwindled so as to be practically useless. It was these two factors which determined the plan to allow the Japanese attack to spend itself while the 14th Army formed a defensive box around their bases at Imphal and Kohima while General Stratemeyer, commanding the Eastern Air Command, was able to supply the 14th Army from the air with men and materials, without the menace of Japanese fighter aircraft.

  Imphal was relieved on 22 June 1944, and shortly afterwards, their supply lines cut by the monsoon and ravaged by disease, the Japanese were forced to withdraw. Of the 85,000 troops in the enemy invasion force, less than a quarter were still fit to fight. But despite these difficulties and their lack of air support, their retreat was typically stubborn. The 14th Army pursued the Japanese back across the Chindwin, setting up bridgeheads on the eastern bank of the river and regrouping in anticipation of a renewed advance, once the monsoon came to an end, on the central Burmese town of Meiktila. The codebreakers were providing Slim with a wealth of information on the retreating Japanese forces. ‘Evidence was now coming in to me daily of the extent of the Japanese defeat, of their losses in tanks, guns, equipment, and vehicles, and of the disorganization of their higher command,’ the British commander said.

  One of the key reasons for the Japanese defeat was the air superiority enjoyed by the Allies, in part at least due to the ability of the codebreakers to predict Japanese air raids. The Bletchley Park air section had broken a three-figure reciphered army air-to-ground code, kuuchi renraku kanji-hyoo 2-goo, known to the British as BULBUL. By the late summer of 1944 it was clear that this would provide vital tactical intelligence and should be worked on in India rather than Bletchley.

  Traffic from the army air operational flying units based around Meiktila was particularly valuable, allowing the Japanese air section to produce detailed intelligence on all their activities. ‘It is thought that this is the first time that the complete correspondence of a number of stations on a particular network and in a particular cipher has become readable,’ Joe Hooper said in a report to Arlington Hall. ‘The correspondence is actually that of the operational flying units in the region reporting aircraft movements; revised unit dispositions before operations; accounts of operations; fuel stock on advanced airfields; Japanese air losses and claims; and DF data.’

  An agreement was reached with the WEC that BULBUL should be taken over by the outstations in India while Bletchley Park concentrated on the high-grade four-figure codes. Although good progress had been made at Bletchley on rebuilding the BULBUL codebook, the capture of a book and some additive sheets from a Japanese aircraft shot down over India made the task of reading it even easier, and by November many of the messages were being intercepted, decoded and sent out as finished intelligence within the space of ninety minutes.

  Michael Kerry was one of the codebreakers assigned to the BULBUL c
odes.

  When we started reading things regularly, five of us went down to Comilla. We travelled by train and had to change railway lines in Calcutta. The two different lines were on either side of the Hooghly River and I have this very vivid memory of the five of us with fifteen porters solemnly trudging across the Howrah Bridge to get to the other station.

  There was an interception unit at Comilla and we joined that and we read quite a lot. The Japanese bombers used to be kept safely down in Bangkok and then when there was a full moon they were moved forward to Mingaladon air base in Rangoon.

  The codebreakers were able to monitor the flight from Bangkok to the Burmese capital and to give warning of the impending air raids. ‘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 allocation of the various high-level army codes had been firmed up during a conference at Arlington Hall in early 1944 and by the autumn the only Japanese military codes being worked on at Bletchley Park apart from JMA were: the Army Air Force General Purpose Code, designated 3366; its Burma area variant 6633; and the Air Safety Service Code, koku hoan angoo-sho No. 1, designated 3636.

  Since Bletchley Park was now the central authority for the Allied codebreakers on all Japanese Air Force codes and ciphers it made sense that they should all be concentrated under one roof. So the military section's army air experts were transferred over to Hooper's Japanese air section. Among those working there was Tony Flew, a linguist who had been due to go to Oxford on a scholarship before becoming involved in a tug-of-war between the university and RAF intelligence.

  Some time in 1942 while I was doing a couple of turns at Oxford the word went out for applications to study East European languages. I won one of the scholarships. But before I could get my RAF service deferred I got my call-up papers. There was then a bit of argy-bargy over whether or not I should be allowed to go on to study Russian and in the end there was this curious auction between the university and the RAF which suggested other languages I might study instead. We eventually settled on Japanese and I then spent a year at the School of Oriental and African Studies. I was very much the odd bod. I was in civilian clothes and all the rest of my course were in uniform.

  He was initially posted to the Inter-Services Topographical Department based at the New Bodleian in Oxford, collecting topo-graphical intelligence on Japan, but in June 1944 was sent to Bletchley Park.

  By now, I was a flying officer. There was a whole lot of us, I would guess around ten, deciphering material that had been sent to us from elsewhere. Alexis Vlasto was in charge. We used captured army air force codebooks, heaven knows how we had ever captured them, to decipher four-figure army air force traffic and then translate it. It wasn't all plain sailing, I must say. You often found that there was a corrupt group and you had to work out what it might have been. We sent the translated messages on and they were radioed out to advance units. The army air force messages were also being deciphered at Comilla and it might seem more sensible to do it there closer to the front line, but the medical situation being what it was it was remarkably more efficient to do it at BP, where none of us ever reported sick, or much less frequently, at least.

  Flew was billeted in Bedford and as a result took no part in the Bletchley social life. ‘By the time we got back to the billets there wasn't much time to go anywhere, the occasional trip to the pub or to see a film. Despite what you sometimes hear, food in the canteen at Bletchley was nothing to complain about. We had different-coloured tickets issued to us for each day as vouchers for our meals. As you can imagine, we quickly broke the code to get extra food.’

  The Japanese air section received its material from India, Colombo, Arlington Hall, OP-20-G and from three set positions of its own at the RAF intercept site at Chicksands Priory in Bedfordshire. Bletchley Park's high productivity on Japanese air codes had led to a dramatic increase in size, with nearly 250 people working on the army air material and a much smaller number, around 75, on the navy air operation which during the latter part of 1944 was severely hampered by the frequent changes to JN25 and the continuing lack of assistance from the US Navy codebreakers.

  Slim's 14th Army began crossing the Chindwin in mass at Sittaungom on 19 November. That night W. C. Smith was just leaving the Wireless Experimental Centre when he was called back in. ‘Perhaps the most exciting moment was to come off duty at 2215 hours one night, only to be told to go back immediately and to discover from enemy sources that one and a quarter hours earlier our forces had crossed the Chindwin,’ Smith recalled. ‘I expect some wag said, “We have to learn it from the enemy.” ’

  By the end of January the American and Chinese forces forming the northern thrust of Operation Capital had reopened the Burma Road and were pushing forward into central Burma. The British 15th Corps on the left flank had captured Akyab and the main force of 14th Army in the centre was preparing for a final showdown with the enemy. As a result of the lack of resistance to 14th Army's advance on the Irrawaddy, Slim was expecting the Japanese commander, General Kimura Hoyotaro, to counter-attack as the main British force crossed the river.

  He devised a brilliant deception plan, leaving a dummy 4th Corps headquarters communicating with one division which continued to push forward towards the river north of Mandalay, the old royal capital of Burma, where the Japanese expected the British to cross. Meanwhile, the real 4th Corps cut south, behind 33rd Corps on its right flank, to cross the river 100 miles south of Mandalay. It then drove northwards to encircle the Japanese, who were swiftly driven out of the two main towns of Mandalay and Meiktila.

  The Allied troops were supported by a number of mobile army and RAF intercept units during the advance into Burma. Dennis Underwood was posted from Abbottabad to join ‘C’ (Indian) Special Wireless Group which was attached to Slim's tactical headquarters at Monywa on the Chindwin River.

  After a lengthy rail and river-boat journey across India to Comilla we were put through a short and sharp battle course, having been warned that if we got sunburn we would be put on a charge – this despite the fact we had come from the North-West Frontier! The temperature was 100 degrees Fahrenheit and we were out in the blazing sun, very lightly dressed, but at any event my fair skin did not burn.

  We then flew into Monywa. The unit was in tented accommodation, six to a tent. I found the makings of a charpoy, propped it on some empty boxes and that was home. We were working on lower-level traffic using low-powered transmitters. The set room was a large tent and we lived under canvas. We were much better off than one or two of our smaller units who were somewhat nearer the fighting and living in far worse conditions. There weren't many of us British other ranks and most of the unit consisted of Indian operators who were extremely good. We worked four- or five-hour shifts which was quite enough in the hot and sweaty conditions; after that your concentration went.

  Off duty we swam in the Chindwin River, which was within walking distance. As it was the dry season, it was quite low and only about 400 yards across with a pleasant sandy beach and a sunken river-boat to play around and dive off. While we did this we got our clothes washed by some of the local population who were happy to be paid in cigarettes.

  As the Japanese retreated we moved south and flew the unit with all its equipment to Meiktila. The aircraft we went in was very heavily loaded and on trying to take off the pilot was unable to get the tail plane to lift. So he came to a halt, came back and asked us all to move forward up to the front of the plane on top of all the equipment. Then he tried again. This time he made it but was not able to get very high. Fortunately, we were over the central Burmese plain and so we staggered on to Meiktila.

  The Special Wireless Groups were fairly large operations with around 300 men and a dozen officers. Smaller Special Wireless Compa
nies, around a third of the size, were attached to each of 14th Army's three corps, and similar-sized units were with the rear elements at Shillong, Imphal, Chittagong and Cox's Bazaar. Each unit had an Intelligence Corps Wireless Intelligence Section alongside it to interpret and analyse the intercepts and to carry out basic code-breaking. The RAF had 355 WU at Calcutta; 367 WU in Cox's Bazaar; 368 WU with TAIS in Comilla; and 358 WU attached to Slim in Meiktila. Underwood said:

  Our leisure time was again spent swimming in a large lake near by. It had small fresh-water crabs in it, although they never seemed to bite. Our drinking water came from this lake and it was rumoured that Japanese dead had been dumped in it. I never saw any but the drinking water had to be heavily treated and had an appalling taste. Snakes were plentiful; we suspected the heavy shelling had disturbed all their usual habitats and it was not unusual to find a cobra in the tent. Fortunately, they seemed as scared of us as we were of them but mosquito-nets were tucked in more securely here than anywhere else I got to. This had been the scene of very heavy fighting and dead Japanese were only a little below the surface where dugouts had been bulldozed over. Our latrine had a dead Japanese mounting guard over it and, as the body had been booby-trapped, no-one wanted to move it.

  The capture of Mandalay allowed motorized elements of 4th Corps to push forward along the central railroad while 33rd Corps advanced down the bank of the Irrawaddy and 15th Corps at Akyab prepared to hop down the coast to make an amphibious landing, south of Rangoon. The monsoon rains began just as the British troops converged on the Burmese capital. On 2 May an RAF Mosquito pilot flying over the city saw a message written by PoWs on the roof of Insein Jail announcing: ‘JAPS GONE.’ He landed his aircraft at Mingaladon air base and walked into the city centre where he visited the British PoWs and assured himself that the Japanese had indeed withdrawn. He then commandeered a sampan and sailed down the Rangoon River to meet the forward elements of the amphibious force and cheekily announced that the Burmese capital had been captured by the RAF.