It is a marked contrast to the policy of outgoing leader Jeremy Corbyn, a passionate and long-standing advocate of nuclear disarmament.
Ms Long-Bailey, a staunch defender of Mr Corbyn’s failed leadership of the party, has previously been accused of being his “continuity candidate”.
Asked on BBC Radio 4’s Today programme whether she would be prepared to launch a nuclear strike, Ms Long-Bailey said: “If you have a deterrent you have to be prepared to use it.”
But she added: “I’m not going to be a warmonger foaming at the mouth and saying that I’m going to press a button.
“Because any leader needs to ensure that they assess the situation, they address the consequences of their actions.
Any leader needs to ensure they assess the consequences of their actions, says MP
“And, of course, any country that was considering pushing the nuclear button needed to realise that we were facing nuclear annihilation right across the whole world.
“But, yes, a leader would need to be prepared to engage in that if they were going to use the nuclear deterrent going forward.”
The Salford and Eccles MP launched her leadership campaign on Monday night, saying: “We need a proud socialist to lead the Labour Party, driven by their principles and an unwavering determination to see democratic socialism in our lifetime.”
Read more from Yahoo News UK
Ms Long-Bailey is currently the bookmakers’ second favourite to win the contest, behind Sir Keir Starmer.
The winner will be announced at a special party conference on 4 April.