In the WW2 time period, Kim, landing almost anywhere in the west would have been fairly futile as a starting point for an invasion of the entire country because then, as now, the population is highly concentrated on the east coast, only more-so then than now. There is still almost nothing between Perth & Adelaide except a single railway line & a road. However, it would have given them access to a vast range of mineral deposits, if they could get them out of the ground. Most of the current mining operations get their water supplies from the post-war Ord River Scheme dams.
To take
Australia, though, an invader merely needs to take the east coast but to take it from the north down the coast leaves a limited front to attack through. Sydney, for example, from the Heads (where the Harbour meets the sea) to the Blue Mountains (which are a part of the Great Dividing Range) is only about 50km (
+/
-). Also, all of the rivers run west-east, from the mountains to the sea, across the path of advance. Awkward for an attacker, good for a defender.
Since starting to seriously consider this scenario, my thinking is that a Japanese attack on Australia would have been staged from New Caledonia. With landings at either Newcastle (north of Sydney) or Woollongong (south of Sydney), or both, because both places have good harbours & would not be as heavily defended, nor as easy to defend, as any Sydney landing points.
Others may thing differently & I'm waiting for their responses, so that I have more information to work with.
Having now lived on 2 islands occupied by the Japanese during WW2, one in the Pacific & the other here in the Indian Ocean, & learning of what happened to those who lived here during the occupations gives one an interesting perspective on the lengths to which the Japanese were willing to go to acheive their goals.
Anyway.
Waiting
Guy