Scottish Labour party delegates have backed a vote to scrap the UK's Trident nuclear missile system, which is based at Faslane naval base on the Clyde.
A motion at the party's conference in Perth calling for the system not to be renewed was supported by an overwhelming majority.
Both party members and unions voted 70% in favour of the motion.
It means Labour now holds different positions on the issue north and south of the border.
However, UK leader Jeremy Corbyn supports not renewing the system.
Analysis by BBC Scotland Political Editor Brian Taylor
The Scottish Labour party now has a policy of opposition to Trident. The extent of the vote makes that verdict incontestable. It will permit Labour members to counter the SNP - who have a long-standing anti-Trident position.
But in practice, what next? Scottish Labour routinely opposed nuclear deterrence in conference votes throughout the 1980s and 1990s, with zero effect.
Might that change now? Not in the short term. The replacement of Trident is a Westminster decision and the Conservatives have a Westminster majority.
Beyond that? Might Labour throughout the UK now adopt an anti-nuclear stance? Certainly it has a leader in Jeremy Corbyn who favours such an approach.
Still, as one seasoned party observer noted in Perth, Scottish Labour now has a supporter of multilateral disarmament leading a party which has endorsed unilateralism. It is conceivable, said the observer, that the UK party ends up offering the mirror image.
After the vote, a spokesman for Mr Corbyn said: "Scottish Labour Party members have spoken. That will now feed into the wider UK Labour debate and review of defence policy."
Mr Corbyn's backing for unilateral disarmament puts him at odds with Scottish Labour leader Kezia Dugdale, who instead supports the removal of nuclear weapons on a multilateral basis.
But Labour's only surviving Scottish MP insisted the party could have different policies on renewing Trident north and south of the border.
Shadow Scottish secretary Ian Murray said moves to make the party in Scotland more autonomous meant it could "have a different position on anything it wants".
Scottish activists made Trident a priority issue for a policy vote at the conference after it received the most votes of the 17 issues proposed for debate.
The conference debate was opened by Stephen Low, of Unison and Glasgow Southside Constituency Labour Party, who said renewing Trident "is something that we do not need and cannot afford".
Mr Low said: "Its purpose is to detonate a nuclear warhead above a city, killing everyone in its radius.
"There are other facts about Trident, but that's the central one, and one we should never forget."
He added: "When it comes to the real threats to this country, things like terrorism, things like cyber attacks, things like climate change, Trident is utterly, utterly useless."
"We shouldn't want Trident renewal even if it were free, but of course it is not free, it comes at an utterly bewildering cost."
Trade union Unison is committed to getting rid of Trident.
During the debate, Davina Rankin from the union told delegates there was no military argument for it and no moral case.
Pat Rafferty, from Unite, which represents Faslane workers, said Britain should take lead in nuclear non-proliferation.
Mr Rafferty said the argument for non-renewal must go "hand in hand" with a jobs diversification plan and the billions saved from Trident could help workers and be used against a "crisis" in industry and the public sector.
However, BBC Scotland has learned that the vote has exposed a rift in the union, with workers at Trident's home base frustrated with the national position taken by Unite's national leader Len McCluskey.
GMB Scotland, which also represents shipyard and defence workers, made clear its support for renewal of Trident.
The union's Gary Smith told the conference the "glaring omission" from the debate was what alternative jobs would be for those working at the base.
Mr Smith said: "This debate is a nonsense and frankly an utter indulgence."
He said the GMB was standing against "Alice in Wonderland politics".
MSP Jackie Baillie, whose Dumbarton constituency includes the naval base, said: "Faslane is the biggest single-site employer in Scotland. More than a quarter of West Dunbartonshire's full-time workforce are employed there in good quality, well-paid jobs."
She hit out at the SNP, who want to move the Trident submarines from the Clyde, describing this stance as "nimbyism on a national scale and the worst kind of gesture politics".
South of Scotland region MSP Claudia Beamish told delegates there was a firm commitment to protect defence workers' jobs regardless of Trident renewal.
Scottish Labour suffered a devastating defeat in May's general election, with the party losing 40 of its 41 seats to the SNP, which has pledged to remove nuclear weapons from Scottish waters.
Analysis by BBC Scotland political reporter Philip Sim
Delegates seemed to thoroughly enjoy a lengthy debate, which featured impassioned arguments from both sides.
But the vocal reception made it clear that the bulk of those in the hall in Perth were behind the motion to oppose Trident.
The result was almost a formality, with delegates cheering as the margin of victory was read out.
In a way this may not be hugely surprising; prior to devolution, Labour conferences north of the border regularly voted against nuclear weapons.
But this was a significant moment for the autonomy of Scottish Labour, as a distinct party from the UK-wide movement.
Not only is it taking a stance on matters reserved to Westminster, there is now clear policy water between the two parties - although leader Jeremy Corbyn will actually be happier than most about this.
As an avowed opponent of Trident, he may well use today's vote to put pressure on party members south of the border to follow suit.
The reaction of Kezia Dugdale, who all but sat on her hands throughout the debate, will be something else entirely.
She used the weekend to set out her stall as the leader of a separate, distinct Scottish Labour party - but as this vote shows, it is a party which is not going to let her have everything her own way.
Where do the parties stand on Trident renewal?
Conservative leader and Prime Minister David Cameron has always maintained the UK needs to keep its nuclear weapons, calling it as "insurance policy" against attacks. Replacing Trident was a Tory manifesto pledge in the general election.
Labour has supported Trident renewal, saying it has been a "cornerstone" of peace and security for nearly 50 years - but that policy is now in doubt after the election of long-time opponent Jeremy Corbyn as party leader. He says the issue will form part of their defence review, but has also said that even if there were a replacement system, he would never use them as PM.
The SNP, which now has 56 MPs in the House of Commons, opposes Trident renewal. During the election campaign it described Trident as "unusable and indefensible - and the plans to renew it are ludicrous on both defence and financial grounds".
The Lib Dems, who insisted on no final decision being taken while they were in coalition, have always been sceptical about a like-for-like replacement and insisted on a value for money review. They back a "step down the nuclear ladder" with a smaller nuclear weapons system providing a "minimal yet credible" deterrent.