▁Australian ▁waters ▁immediately ▁after ▁the ▁attack . ▁The ▁first ▁reconna issance ▁flight ▁went ▁un not iced , ▁and ▁although ▁FR U ME L ▁intercept ed ▁the ▁report ▁and ▁distributed ▁it ▁to ▁Al lied ▁command ers ▁on ▁ 3 0 ▁May , ▁Mu ir head - G ould ▁apparently ▁did ▁not ▁react . ▁New ▁Zealand ▁naval ▁authorities ▁detected ▁radio ▁ch atter ▁between ▁the ▁Japanese ▁sub mar ines ▁on ▁ 2 6 ▁and ▁ 2 9 ▁May , ▁and ▁although ▁they ▁could ▁not ▁dec rypt ▁the ▁transm issions , ▁radio ▁direction ▁finding ▁indicated ▁that ▁a ▁sub marine ▁or ▁sub mar ines ▁were ▁approaching ▁Sydney . ▁The ▁Al lies ▁considered ▁dispatch ing ▁an ▁anti - sub marine ▁pat rol ▁in ▁response ▁to ▁the ▁ 2 9 ▁May ▁fix , ▁but ▁were ▁unable ▁to ▁do ▁so ▁as ▁all ▁anti - sub marine ▁craft ▁were ▁already ▁committed ▁to ▁protect ing ▁a ▁north bound ▁tro op ▁con voy . ▁The ▁only ▁response ▁to ▁the ▁second ▁reconna issance ▁flight ▁on ▁ 2 9 ▁May ▁was ▁the ▁launch ing ▁of ▁search ▁plan es . ▁No ▁other ▁defence ▁measures ▁were ▁put ▁into ▁place . ▁Although ▁the ▁m idget ▁attack ▁on ▁Diego ▁Su are z ▁in ▁Mad agas car ▁occurred ▁on ▁the ▁morning ▁of ▁ 3 1 ▁May ▁( S yd ney ▁time ), ▁the ▁Al lies ▁sent ▁no ▁alert ▁to ▁other ▁command ▁regions , ▁as ▁they ▁believed ▁that ▁V ich y ▁French ▁forces ▁had ▁launched ▁the ▁attack . ▁ ▁Histor ians ▁have ▁question ed ▁the ▁compet ence ▁of ▁the ▁senior ▁Al lied