The Commons voted overwhelmingly to renew the Trident nuclear deterrent system as Labour leader Jeremy Corbyn was angrily condemned by his own MPs for opposing the measure.
MPs voted by 472 votes to 117 in support of a Government motion to replace the ageing Vanguard submarine fleet carrying the missiles with four new vessels.
The overwhelming victory came after Theresa May, in her first Commons speech as Prime Minister, confirmed she would be prepared to authorise a nuclear strike if necessary.
Mr Corbyn, a long-standing opponent of nuclear weapons, came under fire from his backbenchers over his opposition to Trident and the replacement of the Vanguard boats.
Labour split three ways, with the majority of the party's MPs voting in favour of renewing the Trident system - in line with the opposition's official policy - while others abstained or, like Mr Corbyn, opposed the motion.
Mr Corbyn repeated his position that he would not be prepared to press the nuclear button if he was in Number 10, arguing that threatening "mass murder" was not the way to handle international relations.
But a series of Labour MPs lined up to challenge him about his support for unilateral disarmament in the latest public sign of discontent over his leadership.
Labour MP Toby Perkins, who last month resigned as shadow armed forces minister, compared Labour frontbench opposition to Trident with the arguments "of a 13-year-old".
Jamie Reed, Labour MP for Copeland, launched a blistering attack on his leadership's position and warned it could split the party.
He branded Mr Corbyn's opposition "juvenile" and "narcissistic" and said shadow cabinet members who voted against Trident should resign and return to the backbenches because they would be voting against Labour Party policy.
Mr Reed said: "I urge all colleagues on the Labour frontbench tonight to respect the democratic processes of the Labour Party, to respect the conference decision of the Labour Party, to vote with the established policy of the Labour Party.
"And if you can't do that, return to the backbenches."
John Woodcock, in whose Barrow and Furness constituency the new boats will be built, said: "For the official opposition to have a free vote on a matter of such strategic national importance is a terrible indictment of how far this once great party has fallen.
"There has long been a principled tradition of unilateralism in the Labour Party, I myself was born into it.
"But what Labour's front bench is currently doing is not principled. It shows contempt for the public, for party members and, often in what they say, for the truth."
Mr Corbyn used the Commons debate to reiterate his opposition to the potential use of the weapons - one of the key elements of the doctrine of nuclear deterrence.
He said: "I make it clear today that I would not take a decision that kills millions of innocent people. I do not believe the threat of mass murder is a legitimate way to go about dealing with international relations."
His comments came after Mrs May was challenged over whether she would be prepared to authorise a nuclear strike that could kill thousands of "innocent men, women and children".
She replied firmly: "Yes. The whole point of a deterrent is that our enemies need to know that we would be prepared to use it, unlike the suggestion that we could have a nuclear deterrent but not actually be willing to use it, which seemed to come from the Labour front bench."
Setting out the case for remaining a nuclear power, the Prime Minister told MPs: "The threats from countries like Russia and North Korea remain very real. As our Strategic Defence and Security Review made clear, there is a continuing risk of further proliferation of nuclear weapons.
"We must continually convince any potential aggressors that the benefits of an attack on Britain are far outweighed by their consequences.
"And we cannot afford to relax our guard or rule out further shifts which would put our country in grave danger. We need to be prepared to deter threats to our lives and our livelihoods and to those of generations who are yet to be born."