Southwestern Pacific Operations

   After most of his forces in the Philippines were conquered in early 1942, General Douglas MacArthur was ordered to Australia as Commander of the Southwest Pacific.  His first headquarters was at Melbourne but later moved to Brisbane.  In MacArthur’s intelligence chain were Chief of Staff Brigadier General Richard K. Southerland, G-2 Colonel Charles A. Willoughby and Colonel Spencer B. Akin.  Akin produced Army radio intelligence as the head of the joint U.S./Australian Central Bureau at Brisbane. Willoughby analyzed most of it and Southerland decided what would be passed on to MacArthur. Akin retained the authority to bypass Willoughby on certain sensitive reports.  Willoughby did not fully appreciate radio intelligence and tended to rely on his own intelligence intuition, thus often making inaccurate intelligence estimates particularly in the early part of the war.  Although Central Bureau was supported by SIS, who had changed it name to Signal Security Agency (SSA), MacArthur kept the Bureau fairly independent of any SSA control.

    MacArthur had administrative control of considerable U.S. and Australian naval forces in his area including the combined U.S. Navy and Australian Navy radio intelligence operation called Fleet Radio Unit Melbourne (FRUMEL).  The latter consisted of Station Cast personnel that had been evacuated from Corregidor and augmented by Australian men and women naval personnel as well as additional personnel from the U.S. proper.  However, its operational control remained with OP-20-G.   Due to the paucity of intelligence from Japanese Army traffic by SSA and Central Bureau, most of the hard radio intelligence initially came from FRUMEL, Hypo and even Station AL.  Fortunately, many Japanese Army movements and activities were found in Japanese naval communications allowing U.S. naval decrypts, traffic analysis and HFDF fixes to provide considerable intelligence as to Japanese Army and Japanese air intentions and dispositions.  The first high level decrypts of Japanese Army traffic by SSA and Central Bureau were made in April 1943.  Even then, the Army called on two experienced translators from FRUMEL to help with Japanese military and communications jargon.  By 1944, SSA and Central Bureau were producing Japanese Army decrypts on a large-scale basis.  This was helped by the capture of the complete Japanese Army code library at Sio, New Guinea in January 1944.

     Throughout the war, naval radio intelligence reached MacArthur via several channels. In 1942, FRUMEL’s OIC, Commander Rudolph J. Fabian, reported daily to MacArthur’s office and briefed the general and his chief of staff on all information obtained or received from Japanese diplomatic and naval communications although operational control of FRUMEL resided in the Seventh Fleet Intelligence Officer and OP-20-G.  When MacArthur moved to Brisbane, FRUMEL transmitted a daily radio intelligence summary to the naval staff officer with MacArthur’s Southwest Pacific Headquarters.  This officer conducted the navy’s daily briefing to MacArthur.  As a theatre commander, MacArthur also received the U.S. Navy’s radio intelligence summaries and bulletins from CinCPAC and Washington by radio.

    Naval radio intelligence predictions on 16 April 1942 of the planned Port Moresby attack were previously discussed under the Battle of the Coral Sea.  Willoughby received the same intelligence but reported that the attack would be on the Australian coast or New Caledonia since carrier aircraft were involved.  Finally, Willoughby reversed himself, which often became his habit.  After Coral Sea, it was naval radio intelligence that forewarned MacArthur of the Japanese Army’s overland attempt to seize Port Moresby and allow for a counteraction effort, primarily by Australian troops.  Naval analysts were able to track Japanese Army units supported by naval communications through decryption of the WE WE address cipher used to deliver messages to Army units over naval communications circuits.  This applied to Japanese Army units in New Guinea as well as in the Solomons.  Naval Special Landing Force (Japanese Marine) detachments in New Guinea and the Solomons were also located by WE WE addressed messages.

   On 27 July, naval radio intelligence predicted a convoy would arrive at Buna two days later.  Alerted, Allied airmen attacked the ships forcing one transport to beach itself.  A subsequent night bombing crippled the surviving transport, which limped back into Rabaul harbor.  Major General George C. Kenney, MacArthur’s new air chieftain, became one of the most receptive of naval radio intelligence clients on MacArthur’s staff.

   U.S. Navy’s decryption of a submarine picket line blockading the approaches to Milne Bay foretold the location of the next anticipated Japanese movement.  In response, MacArthur rushed Australian reinforcements to the threatened area and air surveillance was stepped up.  The resultant Allied victory at Milne Bay checked the Japanese advance.

   The Royal Australian Navy had established a Coastwatcher network in the Bismark Archipelago and New Guinea similar to the one setup in the Solomons.  This network provided warnings of many convoys and aircraft departing Rabaul destined for New Guinea and also served as a cover for the radio intelligence information as to enemy movements.  However, only radio intelligence could provide advance notification of Japanese deployments.  For example, Hypo warned MacArthur on 2 December that the Japanese would stage fighters at southern New Britain to cover the next Buna convoy.  Forewarned of the fighter escort, American B-17 pilots altered their tactics.  They struck the convoy in successive waves.  When the Zero pilots wheeled after one wave of bombers, another wave arrived to bore in on the ships.  These tactics caused the Japanese Army commander at Rabaul to request the Navy to abort the supply run and return to base.  Runs predicted by radio intelligence were successful only when bad weather prevented air attacks.

    On 13 December, Hypo predicted a major deployment in New Guinea.  A later decrypt disclosed the Japanese would first occupy Madang, Wewak and other points on the northern coast of New Guinea.  By 17 December, U.S. Navy radio intelligence uncovered the scope of the Japanese force aimed at Madang.   Forewarned of convoy destinations, Albacore torpedoed and sank the convoy flagship, the light cruiser Tenryu, whose loss was confirmed in decrypts of Japanese messages.  On 18 December, naval decrypts unmasked Japanese plans to construct a series of airfields at Madang, Wewak, Hollandia, and Wakde. Moemi and other enclaves along the northern New Guinea coast.  Attempts to send the 6th Air Division’s command group and bomber pilots of the 45th Squadron from Japan to Rabaul by the light carrier Ryuho was denied when the submarine Drum was vectored to Ryuho. Drum torpedoed the carrier off the Japanese coast and forced it to return with the loss of 45 pilots.

   Naval radio intelligence often gave advance warning of planned Japanese air raids on U.S. forces in New Guinea, including postponements of such plans.  Waiting P-38’s resulting in the loss of eleven Japanese aircraft surprised a 28 December attack on U.S. facilities at Buna.

   In short, MacArthur was dependent on the U.S. Navy for radio intelligence decrypts and other assistance through at least mid-1943 and naval radio intelligence retained a prominent intelligence role in his headquarters throughout the war.  One more example of naval radio intelligence successful support of MacArthur was the advance notification of IJN’s Convoy Number 81 to move the 51st Division to Lae in March 1943.  This advance intelligence allowed Kenney to mastermind a gigantic air ambush that destroyed the transports in what is known as the Battle of the Bismark Sea.  This defeat was so complete the strategic initiative in New Guinea shifted forever from Japanese to U.S. hands.

   Central Bureau expanded to 4,000 personnel and in 1944 it and SSA provided important Japanese Army decrypts that enabled MacArthur to plan his bold leap to Hollandia.  However, one of MacArthur’s intelligence officers observed that their primary source of tactical air information were navy decoded messages with Washington (SSA) decrypts a secondary source and Central Bureau a “relatively minor” third, while another said “MacArthur has been oversold by his subordinates on the quality of production of his theatre agency, Central Bureau….Tactically, the Navy is incomparably superior to Army production.”

   In late April and May 1944, Ultra decrypts helped submarines destroy the Take convoy of reinforcements for Palau and western New Guinea with a loss of 3,900 men.  The 6,800 survivors lost their equipment.

   As were prior landings on Hollandia, the Allied invasion of Biak was supported by TF58.  Admiral Crutchley’s cruiser-destroyer force was positioned by Ultra decrypts to intercept a similar IJN force that intended to attack troop ships.  Search planes vectored by Ultra found the Japanese surface force and the latter abandoned their nighttime attack after firing their torpedoes at long range.  IJN codebooks were captured at Biak on 8 June, but despite specific regulations for their handling, they were mysteriously delayed.

  The large numbers of land forces, ships and air forces that became available to MacArthur and his knowledge of enemy disposition primarily through Army and Navy Ultra sources, allowed him to hit the weakest enemy points in his leap frog campaign through the remainder of New Guinea, Leyte and the conquest of the Philippines.