Missing Pieces: - Royal Australian Navy

Taking The OFFensiVe 1942–45
for new construction escorts, such as sonars from the United Kingdom, were being
delayed or lost to enemy action, and there was little effective at-sea practical ASW
training capability in Australia. 314 In the Allied Air Forces order of battle there were
insufficient aircraft and aircrew to provide the necessary level of ASW cooperation
and deterrent patrols. Finally, as has been observed previously, General MacArthur’s
SWPA was of low priority to CCS Governments when it came to the strengthening of
its maritime resources.
Fortunately, the Allied forces had some putative advantages in this battle. Besides the
IJN doctrinal and operational experience limitations described previously, the size of
the Japanese boats made them very slow in submerging and, while underwater, they
presented excellent large sonar targets. 315 Their safe diving depth was relatively shallow.
The breadth of the battlefield seized by the IJN diluted the concentration of submarines
to levels well below those faced by Allied forces in the Atlantic, and the generally better
sonar conditions enjoyed in the Pacific made detection of submarines easier. However,
this observation did not apply to the waters contiguous to the Australian east coast,
where sonar conditions were (and are) difficult. For the RAN, the large numbers of
their officers and sailors who had gained experience in battling German U-boats were
potentially a most valuable resource, but few of these personnel returned to the RAN
before the IJN submarine attacks had dwindled. 316
Besides this strategic intelligence, in the early stages of the campaign there appears
to have been little substantive knowledge of the IJN’s submarine force. However, by
the second and subsequent years of the war against Japan this had changed. ONI
Intelligence Report 65—43, Japanese Submarines, of 18 May 1943 contained a great
deal of information on the characteristics of the boats, allegedly based on captured
documents. In September 1943 ONI produced Intelligence Report 84—43, General
Characteristics of Japanese Submarines, which dealt with submarine and weapons tactics.
‘Various sources’ were credited with this information, although the security warning
strongly suggested that Sigint was the basis of some of the data. Both confidential
reports were forwarded to the RAN via the Australian Joint Staff in Washington. In
1944 Allied Air Forces SWPA Intelligence Summary 175 of 22 January consolidated
knowledge about IJN submarines from operational experience, while in June the British
Eastern Fleet issued Intelligence Summary JF/1120 concerning Japanese U-boats. 317
This contained data from interrogations of German U-boat POWs from a boat that had
been based with the Japanese in Penang.
Sigint was of assistance. The IJN submarine force used a separate code, JN-4, which was
broken in June 1942, to report the routine movements of its boats, and these decrypts
were made available to CSWPSF. The Admiralty DF network, supplemented by a local
chain of RAAF DF sites established along the east coast, was frequently able to detect
and fix submarines signalling their post-attack report, as required by IJN doctrine.
Had this information been available regularly, CSWPSF and his NOICs would have had
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