Corbyn, Trident, and the Letter of Last Resort: Legality of Use of Nuclear Weapons

Jeremy Corbyn’s election to the leadership of the Labour Party in the United Kingdom by a landslide victory last month has renewed discussions in the UK about the ‘nuclear deterrent’. Corbyn, a long time anti-war activist and Vice-Chair of the Campaign for Nuclear Disarmament (CND) has, for many years, taken a very public and unequivocal stance against the use of nuclear weapons and in favour of scrapping the UK’s Trident nuclear weapons system. The Trident system is composed of submarine-launched ballistic missiles carried by four Vanguard-class submarines: HMS Vanguard, HMS Victorious, HMS Vigilant, and HMS Vengeance. One of those submarines is constantly on patrol somewhere around the globe. During the recent Labour Party conference, the party failed to take a position in favour of scrapping Trident, but its leader clearly and unequivocally stated that should he become Prime Minister of the UK, he would not use nuclear weapons. For this he was criticized both from within his own party, and beyond, as his statement would mean that were he to become Prime Minister, the UK would have effectively given up the possibility of any deterrent value of its nuclear arsenal.

It might be thought that even if Corbyn were to become Prime Minister the circumstances in which he would have to make a call as to whether to use nuclear weapons are very remote. Far from it! Each new Prime Minister of the UK must decide on the use of nuclear weapons in his or her first few days in office! This is when each new UK Prime Minister must draft the so-called ‘Letter of Last Resort’. This letter contains an instruction from the Prime Minister (indeed the final instruction) to the commanders of the Royal Navy submarines carrying the Trident system. The letter sets out what the commander is to do in case Britain has suffered a nuclear attack that has effectively destroyed the British state, resulted in the death of the Prime Minister and his or her nominated deputies, and led to a loss of contact between the submarine and the UK. There are a number of checks that must be carried out before the commander can presume that the UK has been attacked so devastatingly that nothing of the state and the chain of command remains. Apparently, one of those checks is to establish that BBC Radio 4 is no longer broadcasting! At that stage, the commander of the submarine is to obtain and fulfill the order stated in the letter of last resort, which is kept in the ship’s safe. No letter of last resort has been published. Each one is destroyed when a new PM takes office and issues a new letter of last resort. However, we do have some idea of the options available to the PM, which range from ‘scuttle the ship’, to ‘find and join the US or Australian Navy’, ‘retaliate’ or perhaps even ‘use your judgement’. (For a serious discussion of the Letter, listen to this BBC Radio 4 programme, for a more humorous discussion of the nuclear deterrent, watch this) .

Presumably, Corbyn’s letter of last resort will not involve a command to use the nuclear weapons aboard the vessel. However, it is interesting to consider whether an order to retaliate, in the circumstances in which a letter of last resort is actually opened, would be legal under public international law. To be sure, if such horrendous circumstances were to occur, we would be right at the vanishing point of the utility of law. Indeed, law, as well as other frameworks for organizing human society, would have failed us. However, thinking about whether a use of nuclear weapons (indeed any use of force) would be lawful in those circumstances helps us to understand what we think the purpose of the right of self-defence is, and how it ought to operate in international law.

In considering the question whether a decision by the commander of a UK nuclear submarine to fire the nuclear missiles under his command would be lawful in the circumstances contemplated by the letter of last resort, it is instructive to separate out the question of the legality of the use of nuclear weapons from the more general question of the legality of the use of force in such a scenario. It is now nearly 20 years, since the International Court of Justice rendered its decision in the Nuclear Weapons Advisory Opinion. As is well known, the Court’s decision on the question of the use of nuclear weapons was non-committal and rather ambiguous. The Court, which was even split and decided this point on the casting vote of the President, stated that

‘the threat or use of nuclear weapons would generally be contrary to the rules of international law applicable in armed conflict, and in particular the principles and rules of humanitarian law;

However, in view of the current state of international law, and of the elements of fact at its disposal, the Court cannot conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defence, in which the very survival of a State would be at stake’ (para 2F of what may be called the ‘dispositif’, p 266).

Much ink has been spilt on the interpretation of this passage, and the implications that flow from it (including by one of us in this piece). However, what seems clear is that the Court was leaving open the possibility that in extreme circumstances the use of nuclear weapons might be lawful in self-defence. But the question is in what sort of scenario might that use be lawful. With the letter of last resort, we do have a (more or less specific) scenario: the UK has suffered an attack so devastating that there is no longer any functioning state to speak of. The entire chain of command has been eliminated and the UK no longer exists except in the legal sphere (if at all). Would Article 51 of the United Nations Charter allow the use of a nuclear weapon in self-defence under these circumstances?

To answer this question we need to have a clear idea of what the purpose of the right of self-defence is. It is clear, and well known, that a use of force in self-defence must satisfy the conditions of necessity and proportionality, but what is less clear are the lawful aims or objectives of self-defence. A use of force must be necessary to do what? In broad terms, it may be said that the force must be necessary to respond to an actual armed attack, or to prevent an imminent one. But what exactly does that mean? What objectives may a defending state permissibly pursue in self-defence? Arguably, state practice suggests that when a state is actually suffering an armed attack from another state, the necessity requirement is construed rather loosely. Perhaps even so loosely as to be meaningless. When states are actually under attack from another state it never seems to be required that they seek alternative means or even that they refrain from using force even in cases where it would be futile. In cases of actual and on-going armed attack, there seems to be an almost irrebuttable presumption in law (though not in just war theory) that it is necessary to use force. Necessity only seems to come into its own (as a matter of law) in cases of attacks that are yet to occur, or where the attack is over, or in cases where the attack is by a non-state actor or perhaps against interests of the state abroad (eg nationals attacked abroad). So, to return to our letter of last resort scenario, the question would be whether or not the attack is to be seen as an ongoing attack or one which is over. If the circumstances are such that the UK is effectively destroyed, it is hard to see that this would not be a case where the attack is over. If that is so, then it is hard to see that it can be necessary to use force to repel an attack that is already complete and has achieved its objectives.

What of the proportionality requirement? There are a number of possible meanings of the proportionality criterion but the meaning that arguably has the widest support as a matter of international law (though, again perhaps not in moral philosophy) is that force used in self-defence must be no more than necessary to achieve the objective of repelling an armed attack (or preventing an imminent one). Where the attack has already occurred and has been so successful as to make further attacks unlikely, it is hard to see how force in self-defence can lawfully be said to be proportionate. In such a case, there would no longer be a state there to defend. The right of self-defence would have lost its raison d’être. Any use of force ostensibly in self-defence would be no more than retaliation – an act of vengeance – for a past wrong, rather seeking to achieve the goal of protecting the state from future harm. And self-defence is always about protecting the state from further/future harms to come – even when it is exercised with regard to actual and on-going armed attacks.

In the event that law were to play any role in decision-making in the circumstances contemplated by the letter of last resort, it would seem that a use of force against a completely devastating attack would be neither necessary nor proportional for either repelling an on-going attack or for stopping an imminent one. Corbyn, of course, takes it a step further: no use of nuclear weapons under any circumstances. In that, he may be answering the more general question that the ICJ refused to answer twenty years ago.