A furious new row has erupted within Labour over Trident after Jeremy Corbyn suggested the UK could retain the nuclear missile submarines, but they would go to sea without their warheads.
The plan appeared designed to win over trade unions who fear that scrapping Trident - as the Labour leader wishes - would destroy tens of thousands of jobs in the defence industry.
But the proposal was greeted with derision by pro-Trident Labour MPs, while the Conservatives said it showed that Labour was a "threat to national security".
Mr Corbyn floated the idea during a wide-ranging interview in which he suggested opening up a line of communication with Islamic State (IS) and called for a "sensible dialogue" with Argentina over the Falkland Islands.
Appearing on BBC1's The Andrew Marr Show he also pledged to repeal Conservative trade union laws banning sympathy strikes and did not rule out allowing the return of flying pickets.
On Trident, Mr Corbyn reiterated his long-standing opposition to nuclear weapons but pointed out that the submarines which carry the Trident missiles could be deployed without their nuclear warheads on board.
"They don't have to have nuclear warheads on them," he said. "There are options there."
Shadow defence secretary Emily Thornberry, who is carrying out a review of the party's defence policy, later confirmed she was looking at the "Japanese option" - retaining the capacity to build nuclear weapons without actually possessing them.
"That's certainly one that would be available to us, and that's one of the things that needs to be looked at," she told BBC1's Sunday Politics programme.
But any hopes by the leadership that it would defuse potentially the most divisive issue facing the party were quickly dashed as pro-Trident MPs rushed to pour scorn on the plan.
John Woodcock, the MP for Barrow and Furness, where the replacement submarines will be built, said it was completely implausible.
"Having a deterrent that has no ability to deter because it has no missiles is like having an army with broken rifles and no ammunition," he said.
"It is deeply frustrating because every day that we spend debating implausible schemes like this is a day we are not able to hold the Conservative Government to account."
Mr Corbyn risked further controversy with his suggestion there could be a line of communication with IS – also referred to as Isil – drawing comparisons with the "back channel" between the government and the IRA during the Troubles in Northern Ireland.
"There has to be a route through somewhere. A lot of the commanders in Isil (another name for IS) - particularly in Iraq, but also in Syria - are actually former officers in the Iraqi army," he said.
"Dialogue is perhaps the wrong word to use, but there has to be some understanding of where their strong points are, where their weak points are, and how we can challenge their ideology."
On the Falklands, while Mr Corbyn said the islanders should have an "enormous say" in any discussions with Argentina, he stopped short of saying they should have a veto over any new arrangements.
"I think there has to be a discussion about how you can bring about some reasonable accommodation with Argentina," he said.
"Let's have that discussion, and let's not set agendas in advance."
Mr Corbyn also confirmed he would seek to repeal the laws brought in by Margaret Thatcher's Conservative government outlawing sympathy strikes by trade unions not directly involved in an industrial dispute.
"Sympathy action is legal in most other countries, it should also be legal here," he said.
His comments were welcomed by Unite general secretary Len McCluskey, who said: "I think what I've seen this morning is a Labour leader on the side of the ordinary working people and that's what we've been urging for a long, long time."
However, Defence Secretary Michael Fallon said they showed Labour could not be trusted in government.
"It's clearer than ever that Labour are a threat to our national security and our economic security," he said.