Scottish Labour has overwhelmingly voted against renewing the UK's Trident nuclear weapon system, putting policy north of the border at odds with the UK party's stance.
The vote also means UK leader Jeremy Corbyn and Scottish Labour leader Kezia Dugdale both now have a different view on the controversial issue to their party members.
While Labour's position continues to be to support the continuation of Trident, Mr Corbyn is firmly against nuclear weapons.
Ms Dugdale, who supports multilateral disarmament, watched from the stage as a vote to scrap Trident won just over 70% of the votes at the Scottish Labour Party conference in Perth.
The new Scottish leader has not yet commented on the result.
But the Labour activist who moved the motion hailed it as hugely significant.
Stephen Low, also a member of the Unison trade union, said: "It's without question Scottish party policy now. The Scottish Labour Party is now completely committed to a non-renewal position."
This will feed into UK Labour's policy process, and could help Mr Corbyn persuade his party to back a policy of unilateral disarmament, he said.
Mr Low added the stance in Scotland could help the party win votes in next May's Holyrood elections, and stated: "Every journey begins with a single step, and this was the first step, but it was a significant step, it's a step we're delighted to have taken."
The Trident debate saw trade unions, MSPs and party members all divided over the controversial issue, with the motion backed by 70.3% to 29.7%.
A total of 11,444 votes were cast by members of Constituency Labour Parties, with 70.2% backing the motion, and 29.8% rejecting it. Meanwhile trade unions cast 196,875 votes, with 70.4% voting in favour, and 29.6% voting against.
Afterwards shadow Scottish secretary Ian Murray - who has already said he is opposed to renewing Trident - said he was pleased party members had been allowed to debate the key issue.
Mr Murray, now Scottish Labour's only MP after the general election defeat, said: "My position has always been clear on this, I don't think we should be renewing Trident. I'm pleased the party membership have been given the space - the space created by Kez incidentally - to have these debates today.
"I'm pleased at the democracy of the party and Kezia has been able to re-democratise the party and give the members a real say."
He added: "I thought it was a very high quality debate from all sides, I think it's been great for the party and the members are delighted they've had a say on what is a major policy issue.
"You can't on the one had want to democratise your party and then say you can only be a democratic party if you agree with the leader."
However he could not guarantee Scottish Labour's anti-Trident stance would be included in the manifesto for next year's Holyrood elections.
Mr Murray said the motion had won the two thirds support necessary for it to be in the manifesto, but added that this may not contain a section for reserved policy areas.
He said: "If there is more than two thirds at conference like this then it should automatically go into the manifesto, but there might not be a section in the manifesto for these kind of issues."
Pat Rafferty, Scottish secretary of the Unite union, backed the calls for the nuclear weapons not to be renewed - but stressed this must go ''hand in hand'' with efforts to support workers into new jobs.
He said: ''The argument for non-renewal must go hand in hand with a guarantee that positions, jobs and skills sustained by the current system must be supported by the creation of defence diversification agencies at Scottish and UK level.
''Until we see some commitments to this, as stated in the motion, then trade unions will continue to support the continuity of employment of our members.''
But Gary Smith, of the GMB, said the motion's backing for a ''firm commitment on the retention of defence workers' jobs'', contained no detail about future employment opportunities and pay and conditions.
''This debate is a nonsense, and frankly it is an utter indulgence,'' he said.
''We've closed dozens of yards, we have closed thousands of factories up and down this country, and people have seen what actually happens.
''High skilled well paid union jobs replaced by part-time, low skill, low paid work. Rising levels of unemployment, increasingly levels of poverty - that's what the real alternative is.''
MSP Neil Findlay, who opposes nuclear weapons, told delegates the emphasis must now be placed on reassuring defence workers.
''In this debate, the workforce is key, and we have to give reassurance to the engineers, the technicians, the fabricators and the small business owners that we have a real and genuine plan to create jobs for every worker," he said.
MSP Jackie Baillie, whose constituency includes the Faslane base, said some 13,000 jobs could be under threat if Trident is scrapped.
She 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.''
Adam Ingram, a former armed forces minister at Westminster, said while no moral case could be made for having nuclear weapons, keeping them could allow the UK to influence other countries to disarm.
He argued: "We don't teach by example. What we have got to do is to use our power geopolitically as a proud nation, as one that is a force for good globally, to try to negotiate those weapons away.
"That won't be easy, but by giving them up we would have nothing to negotiate with."
Teenage activist Christopher Rimicans, from Labour's Cunninghame South branch, won cheers from the hall when he gave a passionate speech against renewal.
The 16-year-old said: ''Trident will cost over £100 billion for renewal, we could fund 150,000 more nurses, we could pay for 180 state of the art schools.
''This shows the money could be used elsewhere to make sure we have a better society."
He added: ''The one thing I struggle to understand about Trident is why you would use it in the first place? I'm proud of Jeremy Corbyn's stance against Trident, saying he would not push the button. I think everyone in this room should have the same stance. It's obvious."
But Thomas Docherty, the former Labour MP for West Fife and Dunfermline, said during his time on the House of Commons defence committee he ''did not meet one single serving or retired senior officer in any of the three services who advocated unilateral disarmament''.
But leaders of the other unionist parties in Scotland criticised Labour's decision.
Scottish Conservative leader Ruth Davidson said: "Trident is Britain's last line of defence. It is also a vital part of Scotland's economic security, sustaining thousands of jobs. At a time when the world is growing ever more uncertain, and when Britain's role in the world is desperately needed, the case for renewal is clear.
"The GMB union told Scottish Labour it needed to 'get real' that opposing renewal would cost thousands of jobs. Instead of heeding that warning, Labour has turned its back on vital part of our defence on which thousands of Scottish jobs depend. And it has done so purely in order to ape the SNP in the hope it can win back some of the support it has lost in Scotland."
She added: "I support the retention of our Trident submarines in some form.
"As Jeremy Corbyn leads Labour into chaos and irrelevance, I pledge to stand up for all those people who want to see Scotland remain part of the United Kingdom, and want to see a country protected with a firm line of defence."
Scottish Liberal Democrat leader Willie Rennie said: "At their conference Scottish Labour have confirmed their shift to the left contesting that political territory with the SNP. With the Scottish Tories lurching to the right it leaves a huge space for the Liberal Democrats in the liberal, centre ground.
"Liberal Democrats are building a platform that is pro-environment, pro-Europe, pro-business and pro fairness. It is a positive platform for those people abandoned by the other parties."
UK Labour spokesman said: "The vote reflects Scottish Labour's position and will feed in to the UK-wide defence review."