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Australia’s Turning Point – Signals Intelligence leading to the Battle of the Coral Sea


Australian/American Signals cooperation was not only important in stopping the Japanese advance to Australian shores but marked the beginning of Australia embedding its forces with the United States rather than simply furnishing troops for the British.  Whilst the British, in my opinion, had a long history of using Commonwealth troops to either protect their colonial interests or to take on deployments with high expected rates of attrition, when Australia faced the real possibility of invasion with the vast majority of its troops and equipment deployed overseas, it was the Americans, whose interests in the Pacific aligned with our own, that were on hand to push the Japanese back from our shores.

The Battle of the Coral Sea saw the beginnings of the deployment of Australian sea power under direct American command, a joint approach that would continue to the present time – it was, however, Signals Intelligence that led the way to the embedding of US/Australian forces and played a major role in the outcome of the Coral Sea engagement.

The Beginnings of the Australian Gathering of Japanese Signals Intelligence

In 1921 Lieutenant T.E. Nave of the Royal Australian Navy was attached to the British embassy in Tokyo with the mission of learning to intercept Japanese diplomatic and naval messages.  Although he was proficient in international morse code, the Japanese used their own phonetic version based on katakana containing 71 phonetic codes.  Nave purchased a Japanese morse book from a post office and a set of gramophone records on Japanese and proceeded to learn the language and the corresponding morse.

From 1937 to 1939 Nave was based in Hong Kong and at work listening in on enciphered messages between Japanese ships around the Chinese coast (Japan having taken over parts of the mainland and being in outright war with the Chinese) and their embassies in Hong Kong and Tokyo.  In late 1939 Nave was attached to British Far East Combined Bureau (Intelligence) in Singapore before returning to Melbourne in 1940 to add a Cryptology section to a small Royal Australian Navy signals interception unit.

Direction Finding stations had been established in Darwin, Canberra and Melbourne when Nave was given initial command of Australia’s first Cryptographic Organisation in 1941, run out of Victoria Barracks in Melbourne.  The first Royal Australian Air Force group of ‘volunteers’ began their Special Intelligence course in July 1941 (seven men plus two from the Army).  Due to the speed and complexity of the katakana transmissions the men also learned a developed shorthand to note down the transmissions.  The training lasted for eight intensive weeks.

This first group was ready to be sent to Darwin around 3 September 1941, the trip then taking 11 days.  The group set up two radios at RAAF Darwin aerodrome and worked around the clock in four-hour shifts monitoring messages emanating from Truk (the Caroline Islands), Saipan (Marianas), Palau and Tokyo.  Intercepts were sent to the Navy cryptology department in Melbourne via RAAF signals Darwin.  The work was entirely secret.  The RAAF began to set up its own administrative and intelligence group to learn how to process the information which was the beginnings of RAAF Wireless Units.

The March South

Australian air, ground and naval forces were deployed overseas in Europe, the Middle East and North Africa whilst the war in the Pacific hurtled south.  American and Japanese negotiations were breaking down, with Japanese stationing air groups and 30,000 supporting troops in Saigon and the United States then suspending oil supplies to Japan.  When the Japanese refused to withdraw from Vietnam and China a full embargo was imposed by both the Americans, the British and the Dutch.  The Japanese government fell and a new government led by General Tojo came to power.

Signals intelligence during this time showed detailed Japanese preparations for war, including troop build-ups, surveys, evacuation of Japanese nationals, moving of labourers to strategic points and a raft of other information.  The Japanese made a regular code change on the 1st of November 1941.  On the 19th of November the infamous ‘winds message’ was issued and duly intercepted.  On the 1st of December the Japanese made an unheard-of unscheduled code change – naval unit movements were temporarily lost whilst new call signs were identified, and the Japanese Pearl Harbour fleet set sail.

Whilst all Signals Intelligence pointed to war, diplomatic and foreign affairs expert assessments still believed war with Japan was unlikely – on the 2nd of December Admiral Yamamoto gave the order to “climb Mount Niitaka”.  On the same day a message to the Japanese consulate in Melbourne ordered them to burn codebooks and prepare for the worst.

On the 7th of December the Japanese attacked Pearl Harbour, and simultaneously landed troops in Thailand and Malaya and bombed Singapore.  Within seven days they crippled the US naval base in Manila, virtually wiped out US air strength in the Philippines, sunk the only British capital ships in the Singapore/Malaya area and seized Penang.

Australian Prime Minister John Curtin made the following statement on 27 December 1941:

"The Australian Government ... regards the Pacific struggle as primarily one in which the United States and Australia must have the fullest say in the direction of the democracies' fighting plan. Without inhibitions of any kind, I make it clear that Australia looks to America, free of any pangs as to our traditional links or kinship with the United Kingdom."

By the end of January Hong Kong, Guam, Wake Island and Malaya had fallen and Japanese troops landed in Rabual, New Ireland, New Guinea and the Solomon Islands.  The impregnable ‘fortress Singapore’ fell after a week in early February, Darwin was bombed for the first time on the 19th.  Burma was taken from the British and Borneo and Java were taken from the Dutch by March.   General MacArthur evacuated from the Philippines to Australia in March.


The Defence of Australia

By this stage signals intelligence was the only information available on enemy locations and movements aa there was virtually no reconnaissance information from any sources.  It had proved accurate throughout the first quarter of 1942 although many of the warnings were ignored or simply notice of the inevitable.  Due to the now large number of Japanese Pacific activities, the volume of traffic was tremendous and the process of expanding all related units was begun.

In January when the US evacuated their naval base in the Philippines, their intercept group along with a ‘Purple’ machine (used to read certain Japanese codes) was evacuated by submarine to Melbourne and joined up with a section of the Royal Australian Naval team.  In February MacArthur installed his small intercept group on Corregidor who continued to intercept Japanese traffic.

At 10AM on the 19th of February 1942 Mitsuo Fuchida (the same pilot who had led the first raid on Pearl Harbour) led a force of 190 carrier-borne Zeros and dive-bombers against Darwin supported by 54 land-based bombers from Kendari.  The aerodrome which housed the signals group was a target but the signals building was untouched.  Orders for the four remaining operators to disperse were received.

One went to Wyndham, one to Broome and two to Groote-Eyelandt.  The one bound for Wyndham arrived on the 3rd of March just as the Japanese attacked Wyndham and the plane was shot up on the runway but the officer was unscathed.  The one bound for Broome arrived thirty minutes after a Japanese attack on the town killed at least 70 people.  The dispersal was not successful as the operators were asked to share radio equipment with local civil operators.

In March 1942 the RAAF began setting up an intercept station in Townsville with operators relocating to the North Queensland town.  Priority was given to locating enemy airfields and to intercept signals of Japanese bombers heading for Port Moresby and other Australian held locations in Papua New Guinea as well as Australian targets to give warning of impending air raids.  A further 11 RAAF staff were selected for training.

By the middle of March, the Japanese had captured Lae and Salamaua, just 175 miles from Port Moresby and less than three hours flying time from the Australian mainland.  MacArthur arrived in Darwin on a B17 on the 14th of March during an air raid which meant he was diverted 60 miles south to Batchelor.  He then flew to Alice Springs and a special train was put on to get him to Melbourne three days later.

MacArthur effectively took command of the South West Pacific Area.  He was shocked to learn that extremely limited amount of manpower and equipment for the organised defence of Australia.  Invasion preparedness at that stage meant it was planned to abandon Queensland north of Brisbane should the Japanese land.

Macarthur immediately expanded the existing Signals Intelligence effort.  At the time the American signalmen who had been evacuated to Melbourne sent their information to Washington who then distributed back to area commanders but this was not to his liking for obvious reasons.  He had Major General Akin establish in Melbourne a joint American/Australian signals intelligence organisation called Central Bureau initially using the RAAF group at Townsville as the interceptors.

This is effectively the origin of joint US/Australian military cooperation and is a typical pattern of Australia really needing the manpower and organisation of the US and the US needing Australia’s strategic regional location and utilising it’s well trained and dedicated operatives.

The RAAF was in the process of training the 11 men and was about to begin training 13 women as katakana interceptors.  American operators were finally evacuated from Corregidor.  Central Bureau began operating in Melbourne with cryptographic, cryptanalytic, interpreter and translation personnel along with intercept and communication officers.  These were filled with a mix of RAAF staff and US staff relocated from several locations including Washington.  The mix at the start was 50% American and 50% Australian personnel.

On the 25th of April the Townsville intercept station officially became No 1 Wireless Unit RAAF, less than two weeks before what would be the Battle of the Coral Sea.  By this stage, it consisted of 12 people, 7 RAAF, 1 Australian Army and 4 United States Army (from Corregidor).

Lead Up to the Battle

Following their overwhelming success, the Japanese urged Australia to surrender as defeat was inevitable.  Intercepts on the 17th of April revealed carrier division 5 Zuikaku and Shokaku may arrive in Truk before the end of April and units of the Tainan Air Corps were en route to Rabaul.  The Central Bureau’s comment to MacArthur was that the movements along with extensive air patrols suggested an enemy offensive against Port Moresby before the end of April.

MacArthur believed Port Moresby must be held.  He had only 300 aircraft at his disposal in Australia, half of which were serviceable, and a handful of Australian naval vessels.  He was not in a position to hold off a landing attack on Port Moresby backed up by two carriers.  He initiated air raids against Rabaul and asked for carrier assistance from Washington.

US intercept stations had also arrived at the same conclusion, that Port Moresby was to be invaded by the Japanese.  A decision was taken in Washington to send the carrier Lexington and other available vessels to the Coral Sea area to join United States Task Force 17, which included the carrier Yorktown, to attempt to cut off the enemy attack force as it approached the eastern tip of Papua New Guinea.  This was delayed slightly due to Task Force 17 being in desperate need of some maintenance and the slight delays to the Japanese caused by bombings may have been eventually critical.

A code change due on the 1st of April has been put back to the 1st of May by the Japanese due to delays in distributing codebooks.

By 23 April it was known that the strike force heading towards Port Moresby included the carriers Zuikaku, Shokaku and Ryukaku.  They were due in Truk on 28 April and the attack was set for on or after 2 May.  Intercepts showed persistent bombings would be made on Darwin from 24 April to draw air strength away from the Coral Sea area.

Warnings based on intercepts were issued for possible air attacks on Cape York, Townsville and possibly Brisbane and possible occupations of Tulagi, New Caledonia and Fiji.  An Australian cruiser squadron was heading north to meet up with Task Force 17 in the Coral Sea as the Japanese headed towards their intended landing zone in Port Moresby.

The Battle of the Coral Sea

The first carrier battle in human history began on the 7th of May 1942.  The Australian squadron consisting of the cruisers Australia and Hobart and their escort had diverted to guard the Jomard Passage to prevent the landing fleet gaining access to Port Moresby, a task they would, unfortunately, have to undertake without air cover.

The battle was a pivotal moment in Australian history – the Japanese landing force was turned back and rather than the Japanese establishing themselves on the final stepping stone to Australia they were forced to attempt the same trip overland, with Australian troops fighting to a bitter victory in the jungles of Papua New Guinea.  It also marked an important joint naval operation between Australian and American forces.

Australian Signals Intelligence and the joint cooperation of the Central Bureau directly influenced the course of the Pacific War.  Amongst the stories of naval battles and jungle warfare, the importance of this sort of work is often overlooked, however, its importance cannot be overestimated.

You can read all about the Battle of the Coral Sea here, the focus of this article is Australian Signals Intelligence.

The bulk of the above information is summarised from the early chapters of the excellent Australian book The Eavesdroppers by Jack Bleakley, ISBN 0644223030 – an excellent, succinct and thorough work which I would highly recommend if you can find a copy.


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