Back in the day, we trained to fight against the mysterious Kamarians who's country was located somewhere around where Indonesia is - but definitely NOT Indonesia....
Rumour had it that if the Indonesians had the will, and managed to quickly obtain enough transport ships, they could be halfway across Australia before we were even able to mobilise. A couple of weeks later and Australia would consist of little more than the 400,000 living on Tasmania plus another 50,000 or so refugees from the mainland.
Of course there were a number of prerequisites for that scenario to occur (namely will and transport), but it was a topic of discussion late at night around the Company bar - the consensus was that as a unit we'd hit the hills and do what we could from there.