That blue dotted line reminds me of the red one that the Chinese have slung around the south China Sea. Was this the imagined extent of the Greater East Asia Prosperity Zone that the Japanese envisaged, stopping between those large islands and Australia? The remark about Goshu (Australia) being western lands adds to this feeling that Australia was to be 'outside' and not being considered for invasion. Was the mass attack on Darwin to cut supply routes, yes, but primarily to signify to the west to keep out of Indonesia and SW Asia?