Tony Abbott has called for Australia urgently to consider a missile defence shield to protect against attack by nuclear-armed North Korea.
This means that Australia's two most recent former leaders – one Labor and one Liberal – have now made such a call in the last four weeks.
Australia has no defence against intercontinental ballistic missiles. The government has yet to indicate any interest in acquiring one.
After US President Donald Trump this week said he would deal with Pyongyang's threats with "fire and fury", North Korea said that "only absolute force can work on him".
Foreign Affairs Minister Julie Bishop said on Wednesday that a North Korean ICBM capability posed "an unacceptable existential threat to our country" although she said Australia was "not a primary target".
She said that Australia's strategy was to deter North Korea through international solidarity and called on "all sides" to step back
But Kevin Rudd and Tony Abbott separately are urging defensive steps:
"Of course we should be able to defend ourselves if they have missiles that can reach Australia," Mr Abbott told Fairfax Media on Thursday in his first comments on the matter.
"We should be urgently investing in upgraded missile defences."
Kevin Rudd last month told Fairfax Media that Australia would be "well advised to begin analysing ballistic missile defence needs, available technologies and possible deployment feasibility for northern Australia."
While serving as prime minister, neither man proposed missile defences for Australia. Both now point to new danger.
North Korea last month demonstrated that it can launch ICBMs that experts assess have the range to reach northern Australia.
This week the US Defence Intelligence Agency estimated that North Korea already has a miniaturised nuclear warhead to put atop the missiles, according to US media reports.
Mr Abbott said: "We should upgrade the capability of the air warfare destroyers so they're not just able to track incoming missiles but shoot them down."
"And we should look at the sort of system the US is installing in South Korea," the Terminal High Altitude Area Defence system. Mr Abbott said that the main argument against a missile defence was cost.
"Some would say that it would contribute to an arms race, but it's a race that others are already running," he added.
Experts point out that neither system nominated by Mr Abbott is designed for intercepting intercontinental ballistic missiles but for shorter-range missiles.
However, the most effective missile shields use multiple systems – including shorter and longer range defences – "layered" on top of each other to increase the odds of success.
Missile defence systems are deployed in the US, Japan, western Europe, Israel and other countries.
North Korea said it was devising a plan to fire up to four missiles to land in a tight pattern in the waters around the Pacific island of Guam, a US territory and host to a vital American military base. The military said it would hand the plan to leader Kim Jong-un by mid-August.
Prime Minister Malcolm Turnbull told reporters on Thursday that North Korea was "putting the peace and stability of the region and indeed the world, at risk".
He added: "We note that China has unique leverage over North Korea and we encourage China to use that to bring this regime to its senses."