Subs contract now to be finalised

French shipbuilder DCNS and the federal government will now set about negotiating the details of the $50 billion contract to build 12 new submarines for Australia.

That will take some months.

Sean Costello, chief executive of DCNS Australia, says actual industrial activity will start quite soon, with the construction of a factory at the Techport facility outside Adelaide.

That plant will be larger than Adelaide Oval, he said.

Mr Costello said before they could start building new submarines, they needed to build a new factory.

"As soon as we finish that, we begin the build of the submarine itself. That will be a few years. Between now and then we start to develop all components that go into the submarine," he said.

Mr Costello said the first new boat would be in the water in the late 2020s.

Planning for the new subs has to fit in with other major shipbuilding projects soon to get under way.

Construction of new offshore patrol vessels starts in Adelaide in 2018, then transfers to Western Australia to make way for construction of nine future frigates, scheduled to start in 2020.

DCNS is proposing its FREMM frigate for that project and is one of three firms shortlisted.