 While this was still going on General Marshall , had contacted Brett and asked him to get the Australian government to nominate MacArthur , whose arrival in Australia was now imminent , as its choice for supreme commander . This was done on 17 March when MacArthur arrived at Batchelor , Northern Territory . On 24 March 1942 , the Combined Chiefs of Staff issued a directive formally designating the Pacific theatre an area of American strategic responsibility . On 30 March , the Joint Chiefs of Staff divided the Pacific theatre into three areas : the Pacific Ocean Areas ( POA ) , under Admiral Chester Nimitz ; the Southwest Pacific Area ( SWPA ) , under MacArthur ; and the Southeast Pacific Area , which never became an active theatre . The former Anzac Area was divided between SWPA and the POA . 
