Australia will need to add $30 billion to its military spend if it's to defend itself without help against a potential future attack by a major regional power, strategist and academic Hugh White says.
The nation has to lift its defence spend to 3.5 per cent of national economic activity, much higher than the federal government's 2020-21 spending goal, if it wants to be a self-reliant middle power, he says.
Professor White told an Australian National University leadership forum on Tuesday the federal government's defence spending target of 2 per cent of GDP would leave the nation unable to protect itself against a future attack without the United States' backing. That figure, underpinning the nation's defence strategy, made Australia neither a middle power nor a small one.
"We're spending enough to get into trouble but not enough to get out of it," he said.
Australia's defence budget this year will be $38.7 billion.
Professor White said defence spending was not a test of national virtue or virility, but a policy question of what Australia wanted its armed forces to achieve given old assumptions about regional security may soon no longer apply.
The nation needed to ask itself whether the US would remain the primary power in Asia and would come to Australia's aid in a conflict in the next few decades.
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Anyone who was sure the US would continue playing its past role in Asia would be more likely to settle on a defence spend of 2 per cent of GDP, he said.
Professor White, an ANU academic and long-time defence analyst, expressed doubt that this regional scenario would remain the case, calling the rise of China the most fundamental redistribution of wealth and power in 200 years.
Australia could build armed forces capable of defending the nation alone if it was cost-effective in its defence spending decisions.
A larger investment would be a "hedge" against China becoming an aggressive and intrusive regional superpower, Professor White said.
He admitted the near-doubling of the 2019-20 defence budget needed to achieve middle power status would require a "huge diversion" of resources.
Professor White said he wasn't arguing for the government to take the money from other programs, and asked whether it could be funded with an expansion of the tax base.