ipping ▁between ▁Sydney ▁and ▁New castle ▁was ▁halt ed ▁for ▁ 2 4 ▁hours ▁while ▁aircraft ▁and ▁all ▁available ▁anti - sub marine ▁ships ▁from ▁Sydney , ▁including ▁Dutch ▁light ▁cru iser ▁H NL MS ▁T rom p , ▁Australian ▁destroy er ▁ ▁and ▁US ▁destroy er ▁, ▁searched ▁un success fully ▁for ▁the ▁sub marine . ▁Mu ir head - G ould ▁concluded ▁that ▁the ▁sub marine ▁had ▁operated ▁alone ▁and ▁had ▁left ▁the ▁area ▁immediately ▁after ▁the ▁attack . ▁ ▁I - 2 9 s ▁float plane ▁made ▁a ▁reconna issance ▁flight ▁over ▁Sydney ▁on ▁ 2 3 ▁May . ▁A ▁secret ▁rad ar ▁unit ▁set ▁up ▁in ▁Iron ▁C ove ▁detected ▁the ▁flight , ▁but ▁authorities ▁dismiss ed ▁its ▁report ▁as ▁a ▁gl itch , ▁as ▁there ▁were ▁no ▁Al lied ▁aircraft ▁operating ▁over ▁Sydney . ▁The ▁aircraft ▁was ▁dam aged ▁or ▁destroyed ▁on ▁landing , ▁although ▁its ▁two ▁crew ▁surv ived . ▁They ▁reported ▁the ▁presence ▁of ▁several ▁capital ▁ships , ▁including ▁two ▁batt les hips ▁or ▁large ▁cru is ers , ▁five ▁other ▁large ▁war ships , ▁several ▁minor ▁war ▁vessels ▁and ▁pat rol ▁boats , ▁and ▁pro l ific ▁merchant ▁sh ipping . ▁The ▁report , ▁which ▁the ▁Al lied ▁FR U ME L ▁signals ▁intelligence ▁network ▁partially ▁intercept ed , ▁resulted ▁in ▁the ▁Japanese ▁Navy ▁selecting ▁Sydney ▁as ▁the ▁target . ▁The ▁three ▁m idget - car ry ing ▁sub mar ines ▁rende z vous ed ▁with ▁I - 2 9 ▁and ▁I - 2 1