Labour leadership hopeful Owen Smith said he will vote to renew Trident despite being a former member of the Campaign for Nuclear Disarmament.
MPs are set to vote on Monday night on whether to renew the nuclear deterrent, which is estimated to cost around £40 billion.
Labour leader Jeremy Corbyn is strongly opposed to Trident but has given his MPs a free vote on the issue.
The Times has reported that more than half of Labour MPs are expected to break ranks with their leader and support the nuclear deterrent.
Read more: SNP demand delay to vote on "immoral" Trident
Mr Smith, who is formally launching his bid for the Labour leadership on Sunday, told the BBC's Andrew Marr Show: "I will vote to renew Trident.
"I'm a multilateralist and I believe that the world has actually got more volatile and more insecure over the last few years.
"I want a world without nuclear weapons altogether, but I don't believe that we hasten that by divesting."
He said he abandoned his commitment to unilateral nuclear disarmament 15 years ago as he realised "we need to retain it until we can use it as a bargaining chip to get everybody to get rid of their nuclear weapons".
The former shadow work and pensions secretary also criticised Mr Corbyn for saying that if he became Prime Minister he would not push the nuclear button.
Asked if he would be prepared to deploy nuclear weapons if it came to it, Mr Smith said: "You have got to be prepared to say yes to that, that is absolutely right.
Read more: Leadership candidate warns that Labour risks becoming the "new nasty party"
"It was a mistake of Jeremy's to say that. I understand of course why it is a terrible thought for any person."
Laying out his position, he added: "I want all nuclear weapons in our country and across the world to be got rid of, I don't think that we make that more likely by unilaterally disarming ourselves.
"I don't think we will succeed in encouraging other countries to do likewise, and indeed I think the world has got more volatile so we have got to stick with what we've got, we've got to renew it if that's the advice of the security services.
"And it's awful that we have got to do that, but I'm afraid it's true."
His comments came as the SNP called on Prime Minister Theresa May to delay the parliamentary debate on Trident until the full cost is known.
In a statement reported by the BBC, SNP Westminster leader Angus Robertson said the decision needed "proper scrutiny".
"Trident is an immoral, obscene and redundant weapons system - and the decision on whether to renew it is one of the most important votes this parliament will ever take," Mr Robertson said.
"Having spent the best part of a month engaged in backstabbing, score-settling and navel-gazing, neither the Tories nor Labour are in any fit state to be giving proper scrutiny to decisions as important as this."
Deputy Labour leader Tom Watson dismissed the vote on Trident as "partisan political game-playing" by the Tories because Parliament has already approved the funds to renew the nuclear deterrent.
He drew attention to unions' support for renewal, claiming 30,000 jobs including 6,000 at BAE Systems in Barrow-in Furness could be at risk if it is not renewed, raising the prospect of "ghost towns" and "economic catastrophe".
Read more: Labour leadership hopeful Owen Smith vows to push for second EU referendum
Writing in the Observer, Mr Watson said: "Labour's policy on Trident is clear, but our MPs have been offered a free vote because there is a difference of opinion in the shadow cabinet. I support that.
"But those MPs who vote against Trident should be in no doubt that they are voting to put tens of thousands of defence engineers out of work, many of them members of Unite and the GMB.
"If you are a union general secretary supporting a unilateralist politician, you do so in the knowledge that thousands of your members may lose their jobs."
He dismissed suggestions that Labour MPs should abstain because the party is waiting for the outcome of its defence review, which is heavily focused on Trident.
Mr Watson said: "To do so (abstain) is an abdication of responsibility. No matter what low cunning has engineered this vote, MPs have a duty to take a position. We cannot say to the country that we haven't made up our minds on strategic defence."
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