Opposition Leader Bill Shorten has made an early election promise - if elected in two years time, Labor will definitely build new submarines in South Australia.

Standing outside the ASC shipyard in Adelaide where the navy's six Collins subs were constructed, Mr Shorten said Labor believed in "Aussie" jobs, whereas Prime Minister Tony Abbott's plan was to create jobs in foreign countries.

"Labor, if elected, will build submarines in Australia unequivocally. Labor knows we have world's best practice in these shipyards," he told reporters.

Defence Minister David Johnston retorted that Labor promised in 2007 to build new submarines in SA, then did nothing for the next six years.

Despite reports that the government plans to buy Japanese submarines, Senator Johnston insists no decision has been made and when it is, the government will rely on the advice of defence chiefs.

The debate on defence requirements for new submarines turned into a full-scale row this week, involving the government, opposition, unions and industry.

The new submarines will be the nation's most complex and expensive defence procurement, potentially costing more than $40 billion.

Submarine company ASC built six Collins submarines in SA between 1990 and 2003 and both Labor and the coalition envisaged constructing their replacements in the same yard.

Mr Abbott on Monday implied the work could go offshore.

"The most important thing is to get the best and most capable submarines at a reasonable price to the Australian taxpayer," he said.

He added the government should make decisions "based on defence requirements, not on the basis of industry policy".

It has been reported the Japanese submarines would cost around half the price of an Australian built boat.

Mr Shorten said the government was contracting Australia's national security offshore and disposing of jobs, skills and intellectual property.

Opposition junior defence spokesman David Feeney said Mr Abbott let the automotive industry wither and die and there was concern he would do the same for shipbuilding.

"It is a nonsense to imagine that in a time of crisis we as a country could not build or repair or sustain our own ships and submarines but that is the nonsense being seriously entertained," he told reporters in Adelaide.

Senator Johnston thinks Mr Shorten should apologise to workers over actions of the former Labor government.

"Labor made big promises to SA and proceeded to break them by making massive cuts to the defence budget and putting key projects on the never-never," he said in a statement.

That included former Labor PM Kevin Rudd's 2007 promise to kick start the building of the new submarines in Adelaide.

SA Premier Jay Weatherill said Senator Johnston, who promised last year that submarines would be built in Adelaide, has assured him no decision had yet been made.

"It would be a monstrous act of betrayal if the federal government were to turn its back on those very clear commitments," Mr Weatherill said.