The defence secretary has said Britain's nuclear deterrent is central to its national security.
Des Browne said nuclear weapons were not "inherently evil" and were required to protect against the rise of any dictator who may be willing to use nuclear arms.
Speaking to an audience of academics and students at King's College London, he said Britain had to ask that given this power exists, "is it wrong for us to have it, to deter others from using it against us?"
"In most circumstances imaginable to use that power would be an evil thing to do," Browne said.
"To be consistent, any proponent of the absolutist moral argument must argue that, even were a Hitler to possess a nuclear weapon, it would be morally wrong for us to possess a counterbalancing nuclear force.
"Frankly, I suspect many of us think the opposite - that it is at the very least morally permissible, maybe even morally required, for us to possess a nuclear deterrent under these circumstances."
His comments come ahead of a crucial Commons vote in March on the government's decision to acquire a new generation of nuclear submarines and warheads to maintain the Trident deterrent into the middle of the century.
Many Labour MPs are angered by the move; they argue the weapons are no longer necessary following the end of the Cold War.
But Browne said there was no guarantee that fresh nuclear threats could not emerge in the future.
And he rejected suggestions that the government did not need to make a decision on replacing the Trident system at this stage.
With the new submarines taking 17 years to design and build and the existing submarine fleet coming to the end of its life from 2022, the government had to act now, he said.
"Otherwise we will effectively be committing future generations to disarmament - by depriving them of the option of a credible deterrent."
