Piercing the Fog - Air Force Historical Studies Office

Piercing the Fog
Once secure in New Guinea and then the Halmahera Islands, Allied
commanders drew up formal plans for the assault on the Philippines, Formosa,
and China. As part of this process, the planners reviewed the continuing ULTRA
disclosures and other information, learning a number of key factors in Japan’s
regional defense planning. By mid-September 1944, continuing Allied guerrilla
raids on Japanese garrisons in the Philippines allowed greater opportunity for
intelligence gathering that might supplement the more detached analyses from
Brisbane. Assessments drawn from ULTRA led the Allies to believe that Japan
was carrying out a strategic withdrawal of air units to Formosa, Luzon, and the
home islands, with a consequent reduction in air defenses south of Luzon,
especially the Visayan Islands in the central Philippines. The Japanese air
reaction to carrier air strikes on Yap, Palau, and elsewhere, as reflected in
intercepted messages, seemed one of semiparalysis. Japanese commanders
seemed unable to mount any significant air operations. Despite the fact that
Japanese naval intelligence had located an Allied carrier task force within 300
miles of Leyte, they made no response. The opposite seemed to be true, with a
strengthening of the Formosa-home islands defense line.
The absence of substantial message traffic to Balikpapan in eastern Borneo
indicated a reduction of air defenses around the major oil production and
refinery complex there. Direct evidence from ULTRA illustrated some regional
oil, aviation gasoline, and naval fuel stockpiles. For example, the Japanese
Army Air Force aviation gasoline storage capacity in the Philippines stood at
6.6 million gallons in the Manila area (enough to fuel 166 medium bombers for
30 days), 5.8 million gallons at Hondagua in southeastern Luzon, 3.2 million
gallons at Iloilo, and 2.4 million gallons at Cebu. The Japanese Navy’s air arm
also had storage at Manila, Cebu, and Davao. The Allies surmised correctly that
this storage pattern reflected the relative importance of these areas in Japanese
air operations planning. Balikpapan itself held stocks of an extremely large
amount of aviation gasoline-9.9 million gallons-plus 67,894 tons of fuel oil.
The amounts stored in Borneo, however, were not there for operational use.
This materiel represented a shipping backlog, a result of the constantly
constricting hold that the Allied air and submarine forces had on Japanese
logistics lines.74
Japan’s difficulties in moving fuel to various places along her outer Empire
defense perimeter, and her growing and very serious problems in troop transport
and general shipping, prove the efficacy of Allied aerial and submarine attacks
on her merchant fleet as it moved through the Pacific. From this information
and long experience in the area, Kenney saw achance to make Japan’s problems
even more severe. He believed that the RAAF’s April 1944 mining raids on
Balikpapan’s harbor had badly disrupted transfer of fuel supplies, and he
pleaded unsuccessfully for two groups of B-29s to be based temporarily in
Australia for an attack on Borneo’s oil production. To facilitate acceptance in
Washington of his B-29 suggestion, Kenney had even gone so far as to build
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