Vietnam was Australia’s longest war, and their draft was in full force during the Vietnam war, the draft of neither nation has anything to do with Mel Gibson, he was too young.
Hutton Gibson said that one reason he moved was an effort to keep his OLDEST son from being drafted, he did not think that the Australia draft would take that son.
No one knew how long the war or the draft would last and his sons were all close in age, so, of course he was reasonably concerned that ALL of his sons might be drafted in rapid succession. As far as the Australian draft is concerned, idk, but that's another interesting question. Did they ever become Australian citizens? The old man might have been crazy but "like a fox" shrewd. He also collected some employment disability monies from his job at the railroad, if I recall.