We received Japanese intercepts and one of my jobs was to work on the estimated times of arrival and departure of the aircraft and sometimes the naval traffic. I would keep Captain Nave's book of messages up to date as to the particular whereabouts of these aircraft. Sometimes we would receive plain-text Japanese messages advising of their sightings of Allied ships and aircraft and once in a while they were careless enough to give their latitude and longitude as well as the time of observation. This type of intelligence was usually sent immediately to General MacArthur's HQ which was located about five miles away in downtown Brisbane. Captain Nave was all business. I sat about twenty feet from him for one and a half years but I didn't know until after the war what a well-known cryptanalyst he was and his past accomplishments.
As MacArthur prepared to return to the Philippines, Melinsky was sent to the RAAF's 2 Wireless Unit, which was based near Darwin, monitoring naval air traffic, alongside 3 Wireless Unit, which had responsibility for army air communications. There were about sixty men in Melinsky's unit, all Australians.
They received me politely but were somewhat puzzled by this strange young Pommie who had dropped in from nowhere.
The operational part of the unit was at the top of a hill and consisted of three large lorries with a canvas awning stretched between two of them. Under this I and four or five others worked at tables, with the wireless sets in one lorry and the Intelligence Officer in the other. The third lorry contained generators for providing the electricity. Airmen brought me messages which the operators had picked up listening to Japanese aircraft, and I did my best to decode and translate them. The other traffic consisted of all the other signals sent out by the planes and their bases, and this was carefully examined and collected.
We had a teleprinter link to Brisbane and every message we received was sent down to Captain Nave. Life was very busy when I arrived, with over a hundred messages a day. I started work at eight in the morning, had breaks for lunch and tea and then went back till nine or ten at night. I had a corporal to help me and later two airmen as well. I did not have a day off for three and a half months. The commonest messages were weather reports, which were valuable to us for forecasts. The most exciting were those from and to aircraft escorting convoys and giving their positions. Every evening I sent to Captain Nave a list of code groups which I thought I had broken, together with their meanings, and every morning I received back from him a list confirming them if they were right, correcting them if they were wrong, and giving me additional ones.
The US advance across the central Pacific had meanwhile reached the strategically important Mariana Islands, where Japanese naval messages intercepted by FRUPAC in Hawaii and US Navy ship-borne radio intelligence units would prove vital. One message decoded at Pearl Harbor revealed the exact locations of Japanese submarines forming a defensive patrol line west of the islands. A new ‘hunter-killer’ group of destroyer escorts was sent to attack the Japanese submarines, destroying five as a direct result of the intelligence supplied by FRUPAC. There was one drawback to this US success. The Japanese realized it could only have come from signals intelligence of some sort and changed their procedures, making life harder for the traffic analysts.
The landings by US Marines on Saipan, the first of the Marianas to be attacked, triggered the last large-scale carrier battle of the Second World War. The Japanese 1st Mobile Fleet, including nine aircraft carriers, aimed to squeeze the US 5th Fleet between itself and the land-based air power on the island of Guam. But the Japanese movements were monitored by FRUPAC and the radio intelligence units on board USS Indianapolis, Hornet and Yorktown, allowing the US Navy aircraft to anticipate the Japanese aerial attacks. Only one small group of twenty Japanese aircraft managed to get through, the rest being shot down in a victory so overwhelming that it became known as ‘The Great Marianas Turkey Shoot’.
At the end of 1943, Central Bureau had placed liaison officers at MacArthur's forward headquarters at Port Moresby and the headquarters of 6th Army at Finschhafen. An advanced echelon of Central Bureau was sent to New Guinea in August 1944 to join the forward headquarters which was on its way to a new base at Hollandia, recalled Geoff Ballard, the Central Bureau Liaison Officer.
When we reached Hollandia and drove up to our camp at GHQ, we were overwhelmed by the majestic scene all around us. For sheer, awesome grandeur, this place had no parallel and for us, on our hill at GHQ, it was like being suspended in mid-air. To the north, an immense valley, sweeping up to the Cyclops Mountains with their shapely peaks and girdle of clouds; below us Lake Sentani, of shining mother of pearl, and strewn with green islets like small boats on the surface. In the midst of this grand architecture of nature were the man-made wonders of the US engineers. Within the space of three months they had built two towns – one for GHQ and the other for the 7th Fleet HQ – and to approach them from the valley beneath they had built a highway eight kilometres long.
Back in Brisbane, the size of Central Bureau had increased considerably and had 1,350 staff, 772 of them Americans, including a large Women's Army Corps contingent, 558 Australians, many of whom were members of the AWAS or the WAAAF, 20 British Army and 4 RAF interpreters, and 2 Royal Canadian Air Force code-breakers.
The bureau was divided into eight separate branches, but in terms of intelligence work there were five main branches. B Branch was ‘solution’, comprising the various codebreaking sections. It was led by Abe Sinkov, who dealt with high-grade army systems, and Eric Nave, who was in charge of attacking the codes used for air–ground communications. It also included Professor Thomas Room, who was in charge of a section breaking meteorological codes and ciphers providing advanced warning of Japanese targets. E Branch was traffic analysis, under Captain Stan Clark, one of the Australian officers. G Branch was ‘machine procedure’, the IBM tabulating machine operation based in the three-car garage of 21 Henry Street and controlled by Major Zach Halpin of the US Army. H Branch was translation, under another American officer, Major Hugh S. Erskine. I Branch was general intelligence and liaison, reporting as before solely to the Australian authorities.
The bureau also controlled nearly 3,400 intercept operators, including several hundred women. The forward elements were now 53 Australian Wireless Section, 111th, 125th and 126th Signal Radio Intelligence Companies, US Army, all based in Hollandia, 1 Wireless Unit RAAF based on the island of Biak, off the north-west coast of New Guinea, and 112th Signal Radio Intelligence Company, US Army, which was based in the Solomon Islands.
When the invasion of the Philippines began with the assault on Leyte, on 20 October, General Akin ordered Ballard to make arrangements for an Australian mobile intercept unit to accompany the first landings. The Australian operators were regarded as being more experienced than their American counterparts. A new RAAF mobile intercept unit, 6 WU, was formed, based on a small nucleus drawn from the 1 WU personnel based on Biak, and supplemented by operators sent from 4 WU in Brisbane. General Akin also took a small detachment from the Central Bureau advanced echelon, comprising five Australians and one of the British codebreakers, Peter Hall, with him in the first assault.
The landings on Leyte sparked the Battle of Leyte Gulf, the largest and the last major naval battle of the Second World War and the first phase of the Shoo (Victory) operations launched by Japan as a final attempt to defend the homeland. Naval Ultra was useful but not decisive in the Allied victory. This was largely due to the superior air power of the US Navy and Admiral Kurita Takeo's decision to withdraw just as he had the chance to destroy the 7th Fleet task group protecting the invasion force.
The RAAF intercept unit was operational throughout the journey to Tacloban in Leyte, and was able to report that the convoy had been sighted by enemy aircraft. Once on the ground, the Australian operators soon located the enemy air–ground frequencies and passed warnings of attacks to the US air controllers. They also intercepted details of Japanese convoys attempting to reinforce the Japanese troops on Leyte and were credited with responsibili
ty for the sinking of seventeen ships, including the complete destruction of a convoy of Japanese transports attempting to reinforce Ormoc on the western coast of Leyte. A dozen Japanese naval aircraft escorted the convoy in a concentrated effort to protect it, but it was their radio signals, intercepted by the Australian operators, that sealed the convoy's fate. A mile from Ormoc it was attacked by 347 US aircraft. All five troop transports and four escorting destroyers, including the Shimakaze, the fastest ship in the Japanese fleet, were sunk. The only Japanese soldiers to survive were the few who managed to swim to shore.
Other intelligence garnered from the airwaves by 6 WU included: the location of convoys moving along the Indochina coast; enemy sightings of Allied shipping and task forces operating in the area; air base activity and movements of Japanese aircraft; movements of enemy air formations and high-ranking officers; serviceability reports for enemy airfields; and enemy weather reports. But the most ominous was the creation of a Japanese ‘Special Attack Unit’ of kamikaze suicide pilots at the Clark Air Base on Luzon, the most northerly of the main Philippines islands. The Australian intercept operators were able to plot the flight patterns of the aircraft and volunteer pilots coming in from Japan via Formosa. Many were shot down before they even reached their air base.
The Australian operators and codebreakers, together with their British companion, aroused the curiosity of the war correspondents attached to the US forces, who reported that MacArthur appeared to be accompanied by a small ‘Foreign Legion’.
Back in Brisbane, Central Bureau was also benefiting from the Japanese disarray in the face of overwhelming US military and naval force. The enemy's attempts to co-ordinate the activities of their army and navy air units were providing Eric Nave with large numbers of cribs for the naval air codebook. A Japanese army air unit was co-operating with the Japanese naval aircraft searching for Allied convoys, he said.
The army air unit reported all sightings back to the base in a three-figure code with simple substitution spelling table apparently devised for the purpose. This was most valuable as in addition to being very easy to read these reports had to be re-enciphered in the naval air book for passing to naval air units. These Allied convoy sightings, reports, involving the most carefully prepared section of the book with a vast variety of groups for ship types, courses, etc., were the most difficult to break. However, with the aid of these cribs and the grid system for positions, our information was complete.
In early November MacArthur's GHQ moved to Tacloban, Geoff Ballard recalled.
I was ordered to set up my office in a tumbledown bowling-alley, which was surrounded by a sea of mud. It at least had the merit of a certain isolation. We put up our board by the door which now read ‘Forward Echelon, Central Bureau’ to distinguish it from the Advance Echelon, still at Hollandia. Going to the office was quite an adventure, first stepping along the duckboards over the mud and water, and, once inside, stepping over the alleys to the one level area where we had our tables. Just across the road was the ‘Big House’ where, every evening, we would see General MacArthur, corn-cob pipe in mouth, pacing the long balcony and now and again waving to children in the street below.
The production of Ultra by Central Bureau had continued to expand to the point where Japanese plans and strategy became known to us as soon as they had been formulated and communicated for action to their own forces. Accordingly, it was vital for this intelligence to be available to GHQ at every stage of its planning because its own operations were largely based upon it. As a consequence, my liaison duties assumed a still more intensive role and most days saw an exhausting round of intelligence briefings and discussions not only at GHQ but at the 7th Fleet HQ and aboard the command ship USS Arkansas moored in Tacloban Harbour. My visits to the Arkansas were a special experience. The technical gadgetry in the operations room had all the elements of that in a science-fiction laboratory, particularly of illuminated screens with intelligence items moving constantly upwards upon them.
The capture of the Marianas island of Guam, and the new-found willingness of the US Navy and Army codebreakers to co-operate, allowed the creation of an advanced joint signals intelligence operation. The level of inter-service co-operation was remarkable by US standards. Radio Analysis Group, Forward Area, or RAGFOR, had more than 600 army codebreakers and a similar number of navy codebreakers working alongside each other under the command of a US Navy officer and fed by army and navy intercept operators. It was located far closer to Tokyo than any other Allied static intercept site and was in operation and fully integrated with the US and British sites via the BRUSA Circuit by December 1944. The US Navy element of RAGFOR effectively replaced FRUMEL, which with the battle now having moved far forward of Melbourne was stripped of most of its US personnel and handed over to the Australians.
22
THE ATOMIC BOMB
For several months the Allied codebreakers had been monitoring the build-up of Japanese troops in the Philippines as part of the Shoo campaign, the last-ditch defence of the empire. A combination of messages decoded by Central Bureau and the Japanese military attachés’ ‘Tokyo Circular’ had revealed that a quarter of a million Japanese troops were defending Luzon, the largest and most heavily populated island in the Philippines.
The Japanese general Yamashita Tomoyuki, known as the ‘Tiger of Malaya’ for his role in masterminding the fall of Singapore, believed the Americans would be at their most vulnerable on the island. By December 1944 it was clear that the attempts to reinforce Leyte had significantly reduced his forces on Luzon. When the Central Bureau codebreakers caught him bemoaning the state of the Japanese defenders, MacArthur decided he must strike now or risk further Japanese reinforcements causing serious disruption to the fulfilment of his promise to liberate the Philippines.
As the US troops fought their way across Leyte and MacArthur prepared for the assault on Luzon, the Australian and British ‘Foreign Legion’ based at Tacloban was joined by two US Army intercept units which also came under the control of Central Bureau. The 111th and 125th Signal Radio Intelligence Companies covered mainline army and army air systems, radioing the results back to the codebreakers in Hollandia and Brisbane for decryption.
Central Bureau's army air ‘solution’ section moved to Leyte where the RAAF intercept operators of 6 Wireless Unit had been augmented by a detachment from 4 Wireless Unit to cover naval air traffic. The codebreakers were able to monitor times and targets of planned enemy air raids, details of Japanese attempts to move reinforcements into the region, flights carrying high-ranking personalities and details of weather reports.
When the first US troops came ashore at Dagupan in the Lingayen Gulf they were joined by a detachment of 6 Wireless Unit and their American counterparts from 112th Signal Radio Intelligence Company. The Allied intercept operators hit the beaches within twenty minutes of the first assault but while the RAAF operators were soon at work, their US counterparts were waylaid by army commanders who inexplicably put them to work as a shore party, unloading ammunition, fuel and other supplies for the US troops. It was a week before they were released for their proper duties but eventually they rejoined the RAAF ‘Foreign Legion’ who had commenced intercept operations at San Miguel, the new site picked out for Central Bureau's forward elements.
The ability of the Central Bureau codebreakers to produce useful intelligence was hampered at the beginning of February by a change in the Army General Administrative System codebook which deprived them of a key source of intelligence. Worse, since the Japanese High Command had by now decided that the Philippines were bound eventually to fall to superior US resources, Yamashita's forces were no longer being reinforced and the water transport messages provided little intelligence of any value. But gradually the codebreakers began to rebuild the book, and during the battle for Okinawa in April, a near complete cryptographic library, including the new codebook, was captured, ensuring that they were able to read all the main Japanese Army messages immediately for several weeks a
nd without major difficulty until the end of the war.
Both Central Bureau and the Royal Navy codebreakers in Colombo provided small radio intelligence or ‘Y’ units on the American model for the ships of the recently formed British Pacific Fleet and the US Navy's 5th Fleet. The units, which comprised two officers and fourteen intercept operators, monitored air–ground frequencies in order to warn of any impending Japanese attacks on the Allied ships. The most successful of these parties was that led by Colombo's Lieutenant John Silkin (later a senior Labour Party politician and Environment Secretary in the British Government) during the assault on Okinawa. Silkin's party was on board HMS King George V, the same ship that had brought the first Purple machine across the Atlantic to Britain. Although lacking the experience and knowledge of the known frequencies enjoyed by their US counterparts, they provided an accurate, up-to-date picture of the enemy air activity in the region which was vital in ensuring that the British ships did not fall victim to the increasingly desperate Japanese kamikaze attacks. ‘We were dealing with a beaten and disorientated enemy, whose sole power of retaliation lay in his suicide bombers,’ Silkin said in his report of the operation. ‘These last hopes were foiled, largely by the watch kept by Y parties.’
The invasion of Okinawa saw the Japanese Navy's final attempt to take the battle to the Americans when the Imperial Naval General Staff ordered the super-battleship Yamato to lead a force of one cruiser and six destroyers in a suicidal attack on the US ships supporting the invasion force. But the entire Japanese plan was decoded by the US Navy codebreakers in Hawaii and the ‘unsinkable’ Yamato was sent to the bottom of the ocean by US carrier aircraft along with her cruiser and four destroyers.
The Royal Navy codebreakers at Colombo were given more autonomy over their operations with the creation of their own unit, HMS Anderson, and Hugh Alexander was sent out to revitalize their operations against the key codes JN25 and JN11.
The Emperor's Codes Page 32