I'd say this is probably a better question for /r/HistoricalWhatIf

I'll leave you with Australia's WW2 population. Just over 7 million. Not very much.

hi OP; it's against the rules for respondents to speculate; as such, I'm removing this post. But as mentioned, this question would be appropriate in /r/HistoricalWhatIf ; hopefully the creative minds there can help you out