This is coming out of a political announcement, Australia is having a grand budget spendathon in the lead up to an election which will be called next week.
And this particular article pretends analysis but simply provides the government press release and talking points.
The expenditure is mostly loaded into the last six years, often viewed as the political never-never. Forecasts are performed over the next four years, revenue, deficient etc. By putting the expenditure outside of that period they get to claim spending big without being accountable for it. Additionally, four years is two elections, the current leader and ministers won't be around by then to be held accountable in any way.
The fine print also shows that the funding includes money already allocated to the Defence Integrated Investment Program. That is, money that has already been allocated to be spent has been counted twice, it is not a new "bolstering" of anything except electoral fortunes.
Actual analysts are suggesting a new expenditure of $588.7M AUD over the next four years. Which is 147M AUD / year, or roughly 150M AUD / year.
The other huge asterisk is that the current government is predicted to lose, the opposition and probable incoming government has already said that they will immediately redo the budget. So in three months it will probably all change anyway.