The most common response to the humanitarian concerns raised about nuclear weapons is ‘of course nuclear weapons would never be used, they are merely a deterrent’.

The UK’s nuclear weapons are not designed for military use during conflict but instead to deter and prevent nuclear blackmail and acts of aggression against our vital interests that cannot be countered by other means…

(‘The Future of the uk’s Nuclear Deterrent’ White Paper, 2006)

The British government indeed prefers to refer to its own nuclear weapons, not as a weapons system at all, but as ‘the deterrent’, as if this categorically defines what a nuclear weapon is. But a nuclear weapon is not ‘a deterrent’ in and of itself. Even the BBC acknowledges that in its internal guidance to journalists. Any government possessing nuclear weapons hopes these weapons will act as a deterrent and will never actually be used as weapons. But what does deterrence actually mean?

According to the us Department of Defence, deterrence is ‘the prevention from action by fear of the consequences. Deterrence is a state of mind brought about by the existence of a credible threat of unacceptable counteraction.’ In other words, deterrence is a psychological term, not a military term. It is about trying to create a sense of fear that you hope will convince someone that they don’t actually want to do something they might otherwise choose to do.


As a strategy for controlling someone else’s behaviour, deterrence relies on threatening that person with some form of punishment if they do something you don’t want them to do. Leaving aside whether coercion through fear is morally palatable, ‘successful’ deterrence means the punishment never has to be carried out because the mere threat of it is sufficient to control the behaviour. ‘Unsuccessful’ deterrence is when the threat has to be carried out in order to control the behaviour in question.


Nuclear deterrence

The theory of nuclear deterrence depends upon it working not just most of the time but all the time – and for all time. There is no room for a margin of error if the consequence of nuclear deterrence not working is an all-out nuclear war that destroys the whole of human civilisation.

The ‘credibility’ of US nuclear deterrence furthermore rests completely on the fact that two atom bombs were dropped on Japan more than 70 years ago. While subsequent nuclear tests have shown how enormously devastating the consequences of a nuclear weapon would be, they do not in themselves demonstrate a willingness by the us to use such a weapon. The UK meanwhile has never used a nuclear weapon against another country in anger. This makes it exceedingly difficult to argue that the UK’s threat to use a nuclear weapon is a credible one.

This credibility ‘gap’ is a dangerous one when it comes to nuclear deterrence, because it increases the likelihood that sooner or later a nuclear weapon will be used, if only to send a clear signal to some future adversary that the deterrent is backed up by real intention and willingness to use it.

The logic of nuclear deterrence gets more and more convoluted the deeper one goes into it. It is assumed, for instance, that the leaders of Russia, in contemplating an attack on the us, would be sufficiently sane and rational as to weigh up the consequences of a possible retaliatory nuclear strike from the US and decide on that basis to refrain from attacking. On the other hand, it is assumed that those same leaders would base their sane and rational decision on the likelihood of their counterparts in the us acting so insanely and irrationally as to be willing to launch nuclear weapons against Russia that would almost certainly bring about their own total self-destruction (see Mutually Assured Destruction).

Furthermore, the theory demands that ‘we’ must be willing to use our nuclear weapons if necessary and that willingness must be sufficiently convincing to our opponent that they believe we really will actually use our nuclear weapons if they dared to attack us. On the other hand, if we are willing ‘if necessary’ to use our nuclear weapons against another country which also has nuclear weapons, then at some level we are not ‘deterred’ by them having nuclear weapons. That other country is likewise not deterred by the fact that we have nuclear weapons if it is to be believed that they also would use their nuclear weapons ‘if necessary’ against us.

Ultimately, nuclear deterrence rests on the assumption that no ordinary, sane person would choose to bring death and destruction down upon family and friends and loved ones, and would therefore choose some alternative route other than to invite nuclear retaliation. The problem with this line of thinking is that nuclear deterrence does not operate at the level of ordinary, sane people who care about their loved ones. It operates at the level of generals and politicians who make their decisions according to quite different criteria.

It was the logic of those same generals and politicians who sent millions to their certain death in the trenches of WWI and authorised the saturation bombing of German and Japanese cities and the dropping of atom bombs in WWII. The actual use of nuclear weapons would cause wholescale slaughter on an unimaginable scale, but there is no evidence that such a result would necessarily ‘deter’ generals and politicians from embarking on such a course should they decide the circumstances ‘justified’ it. Indeed, they have been ready to launch nuclear war on several occasions and it is luck, more than ‘deterrence’, which has kept us from having a nuclear war up to now.

Pressing the button

In her first full speech as British Prime Minister on 18 July 2016, Theresa May was asked in parliament if she was personally prepared to authorise a nuclear strike that could kill hundreds of thousands of innocent men, women and children. Her answer was an unequivocal ‘yes’. ‘And I have to say,’ she went on, ‘that the whole point of a deterrent is that our enemies need to know that we would be prepared to use it.’ Nuclear weapons as a ‘deterrent’, therefore, are not somehow distinct from the intention to use nuclear weapons as a weapon.

In the words of the late Sir Michael Quinlan:

We cannot say that nuclear weapons are for deterrence and never for use, however remote we judge the latter possibility to be. Weapons deter by the possibility of their use and by no other route.

We do not know whether any President or Prime Minister really would press the button in the event that Russia or another potential opponent called their bluff and launched an attack anyway. Saying that they would does not by itself make the threat credible. A Russian leader might calculate that actually, if push came to shove, a us president wouldn’t actually press the button even though he said he would. It all comes down to psychology and there are so many unknowns it is impossible to know what anyone would do under any number of possible scenarios. That is what makes the whole theory of deterrence so fanciful.