New subs needed to make Aust safe: PM

Malcolm Turnbull has defended his government's planned $50 billion spend on 12 new submarines, saying it's needed to safeguard the country.

The prime minister dismissed suggestions by radio 3AW host Neil Mitchell that it was an expensive way to create 3000 jobs, especially in South Australia.

"We've got to spend the money to have the means to defend Australia," Mr Turnbull said on Friday

The prime minister also had to defend the decision as he responded to the concerns of a former special forces soldier.

"James, you sound like a soldier asking the question why do we need the navy," Mr Turnbull told him.

On a more serious note, he said Australia had to prepare for potential tensions and conflicts in the region.

"You have to prepare to defend yourself."