The opposition is calling for a re-think on the number of submarines the federal government is planning to build.

This year's defence white paper called for as many as 12 missile-carrying "future submarines" to be built as part of a large military build-up.

"We are waiting for a reasonable explanation from the government as to why you need 12," opposition defence science and personnel spokesman Bob Baldwin told AAP on Thursday.

"There needs to be more dialogue, and I think they need to bring the opposition in."

Mr Baldwin suggested part of the problem was the resignation of former defence minister Joel Fitzgibbon after the release of the white paper.

"Now is the time for (Defence Minister John) Faulkner and (Defence Personnel, Materiel and Science Minister Greg) Combet to stamp their own authority on the white paper and rationalise the number of submarines," he said.

Mr Baldwin questioned how defence was going to run so many submarines given the ongoing struggle to man the navy's ageing Collins class subs.

"What we don't need is a dozen submarines with ten tied up at the wharf and only two operational."

In a landmark speech delivered on Thursday, Mr Combet declared the submarine project one of immense industrial and scientific significance.

"The Rudd government is confident that Australian industry can again rise to the occasion, as it did with the Collins project 25 years ago," Mr Combet said.