Former prime minister Tony Abbott is warning the Government its new fleet of Shortfin Barracuda submarines may not be powerful enough to protect Australia's interests in the Pacific.
He has urged the Turnbull Government to consider nuclear submarines, saying he regrets not giving the technology more consideration when he was prime minister.
"I worry that a decade or so hence, maybe sooner, Australia might face a security crisis in our region and find that governments of yesterday and today had left their successors with inadequate means to deal with it."
The Government signed a contract for 12 new submarines with the French company DCNS last year.
The subs will be built in Australia, modelled off a French nuclear submarine but using conventional power.
Mr Abbott says the submarines will take a long time to build and may be out of date by the time they arrive.
"Now I'm not saying that we must go nuclear, but surely we should at least consider the option before the opportunity is lost for another several decades."
Mr Abbott's speech at the Centre for Independent Studies in Sydney comes at the end of a difficult week for the Government.
He has made several media appearances sharply criticising his Liberal colleague Christopher Pyne for his recently leaked comments on same-sex marriage.
Mr Abbott says he laments the media's fixation with Liberal Party infighting and what he sees as a lack of interest in his policy concerns.
"And it's not nearly as significant to the people who shape our national conversation as whether Person X or Person Y currently has his or her nose ahead in the latest leadership 'brouhaha-ha' in Canberra."
Mr Abbott says nuclear submarines could be purchased from the United States, removing the need to build them in South Australia.
Labor MP Richard Marles has released a statement saying the Opposition is committed to the local build.
And he says the nuclear idea is not realistic, considering the lack of a domestic nuclear industry.
But in his speech, Mr Abbott took the unusual step of praising Labor, expressing hope that Bill Shorten would consider supporting the idea.
"I am confident that, at least under the present Labor leadership, it would get a fair hearing. Labor has actually been stronger than the Government on the assertion of freedom of navigation rights in the South China Sea."
Meanwhile, the Greens are dealing with their own internal division.
The party room voted to ban New South Wales Senate colleague Lee Rhiannon from voting in its decisions on contentious legislation.
She is accused of undermining the Greens' negotiations with the Government over its Gonski school-funding package.
Greens leader Richard Di Natale has told the ABC a New South Wales Greens rule that binds their members to state policy is making national decisions difficult.
"What we have is, in one state where a senator is bound to a particular position, it makes it impossible for us to have a process that's based on consensus, because they're bringing a fixed position into the party room."
Labor has attacked both the Liberals and the Greens for their internal bickering.
The Greens leader says Lee Rhiannon is not being punished.
But deputy Labor leader Tanya Plibersek says the Greens are too divided to negotiate effectively.
"The Government was better able to negotiate with the crossbench than they were with the Greens, and it really seems bizarre that Lee Rhiannon is now being punished for advocating the position that the Greens eventually took in the Parliament anyway. I mean, it's a mess. It's a mess."
