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

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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.

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Jack McDonald says

October 6, 2015

The question posed - whether a nuclear strike in response to the destruction of the British state would be legal - is interesting, and I can't fault the basic legal analysis that follows. However, the explicit/implicit threat of a nuclear response to nuclear attack is the basis for nuclear deterrence, both in the UK, and among other nuclear states. If this threat is manifestly illegal, then so are all similar 'end of the world' protocols and procedures. Nuclear deterrence, then, would be illegal. Given that nuclear weapon states tend to predicate their possession of nuclear weapons on their deterrent capability, this poses a bit of a problem. The legal analysis set forth would (according to deterrence theory) make the world a less stable place - law abiding states, by refusing to launch retaliatory strikes when annihilated - would be vulnerable to massive first strikes by non-law abiding nuclear weapon states. Given that the character of an armed attack using nuclear weapons that is sufficient to extinguish a state would by definition be illegal, then defining retaliations as illegal in this context would be stacking the deck against law-abiding states.

Three alternate analyses:

A) Two people armed with guns, A and B, have an argument. A shoots B, and fatally wounds them. B, with their dying breath, shoots A and kills them. The law that would proclaim B's action to be illegal would seem quite strange to most, and I doubt that anyone would consider B's actions to be unjust. There are obvious non-parallels here - in nuclear deterrence B would be dead, but B's trigger finger (the Submarine commander) would be alive, also, B's bullet would (probably) be killing millions of civilians. Nonetheless, the standard that A could go around murdering people so long as they murder them before they get a chance to fight back would be a strange one.

B) The orders, predicated on an attack that decapitates the state, are considered self defence in response to that attack because they are the only means of preventing such attacks without resorting to preventive or anticipatory self defence.

C) The submarine commander, at the precise moment of launch, is a non-state actor due to the demise of the British state. The act of launching the nuclear weapons is therefore something like an act of terrorism, and whatever state harbours the submarine crew subsequent to the launch is liable to all sorts of penalties if they don't bring them to justice.

All of the above ignores, of course, that if a nuclear attack occurred that wiped out the British state, it would likely be part of a general nuclear exchange that would put paid to the international system/human species. Who would be left to pass judgement?

Dapo Akande says

October 6, 2015

Jack, your point at the end of your comment, in relation to how in this scenario there probably won't be anyone left to pass judgment, is correct. However, our point was just to use the scenario as a way of thinking about what self-defence is for and how we interpret the conditions therefor.

You make a good point about how the analysis poses a problem for the legality of nuclear deterrence. Nuclear deterrence, of course, consists of a threat to use force. In the Nuclear Weapons Advisory Opinion, the ICJ stated that a threat to use force would be unlawful where the threatened force would be also be unlawful. If it is correct that a use force in the circumstances set out in letter of last resort would be unlawful, then, on the ICJ's analysis, the threat would also be unlawful. However, the question is raised as to whether the threat is a valuable one which we should allow, in order to prevent other (prior) violations, even though the force threatened is unlawful. While this may be a useful way of inducing others not to commit violations, it is hard to see that a system of law could indeed allow threats to take unlawful action.

JaKob, the question of whether the action would or would not be immoral is also an interesting one. Perhaps even more important both for the prime minister (when writing the letter), and for the commander, when deciding what to do. Of course opinions will vary but I think that if one examines the criteria set out in Just War theory - particularly the last resort requirement - then one might come to the conclusion that it would also be immoral. My colleague, David Rodin speaks about this in the BBC Radio 4 programme that we link to above.

Anton Secule says

October 6, 2015

The Cambridge U youtube channel has an interesting (albeit unrealistic) short film on the nuclear defense question which tries to sell the issue as a "legal dilemma". This is the link:

Jakob Cornides says

October 6, 2015

When the loyal application of a doctrine to a concrete scenario leads to absurd results, then maybe the doctrine is at fault.

In this blog post, the scenario is that the UK has been effectively wiped out by a nuclear attack, so that "legitimate self-defence" is not possible because there is nothing left to be defended. And I take it that the two authors consider "retaliation" in such a case unlawful or unethical.

But the absurd result of this argument is that another country can effectively wipe out the UK. If it manages to do so in one strike, then it has nothing to fear.

Setting aside the question whether in such a situation would be lawful, I definitely think it would not be immoral. Although there would be no UK left to be defended, the retaliation would at least serve to defend the abstract principle of equity and discourage the aggressor from attacking further victims.

Exoriare aliquis nostris ex ossibus ultor...

Patricia Jimenez Kwast says

October 6, 2015

Thanks for a very interesting post! I would tend to disagree, however, with the conclusion that “it would seem that a use of force against a completely devastating attack would be neither necessary nor proportional for either repelling an ongoing attack or for stopping an imminent one.”

1. Necessity requirement:

You write that “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.”

I would argue the contrary. Even if (nearly) nothing of the UK remains, this would not easily bring an end to the State as a legal entity in international law: presumably the UK would still have (some) overseas territories with a British population, as well as a diplomatic apparatus, security personnel etc. and other nationals operating abroad. So even if “there is no longer any functioning state to speak of”, it would still be a state - one whose survival is very much at risk. You state that in such a case the attack “is already complete and has achieved its objectives”. But judging from the severity of attack that would be necessary before the UK would be “effectively destroyed”, I would say that the attacker presumably or arguably wants the complete annihilation of anything that remains of it (incl. overseas). I find it difficult to imagine a scenario in which the use of force can be any more “necessary” for the survival of a state than this.

Now of course this scenario depends on a presumption that the UK does not suffer an attack that wipes out all its territories, officials, etc. at once. But even if that were to happen, I would still not easily accept that the UK would (legally) cease to exist and that therefore necessity-condition for the exercise of the right of self-defence cannot be met.

2. Proportionality criterion:

You write that it is hard to see how the use of force in self-defence can be said to be proportionate if there would no longer be a state to defend. But I would argue (see 1) that what is left of the UK would still be a state in international law. So the right of self-defence would not have lost its raison d’être. If the use of force in self-defence would be necessary, the proportionality test would be a matter of weighing the survival of the UK against the (massive) harm caused by the exercise of self-defence. This is a difficult but presumably not un-passable test.

Aurel Sari says

October 6, 2015

You seem to focus on individual self-defence. Even in circumstances where the UK is effectively destroyed, might a nuclear engagement not remain a legal option in the exercise of the right of collective self-defence?

T.Flynn says

October 8, 2015

There would be no State remaining - not in terms of what is recognised as a State for the purposes of international law such as the constituent components of a permanent population (obliterated); a recognised government and the capacity to enter into legal relations.

John Paul Jones says

October 12, 2015

A very interesting thought exercise. It seems to presume the end of a state from the desolation of its home islands. I would assume to the contrary duties on the part of the Royal Navy to persist in defense of British Overseas Territories and Crown Dependencies, as well as to respond obediently to a government in exile.

Lee Chirtel says

October 15, 2015

Interesting discussion here, although I fear that the presentation of the question is fairly circular (ala Zeno's paradox of motion).

Indeed, if the existence of the nation/state (the destruction of the United Kingdom as a state might not extinguish its citizens as a national body) is necessary for self defense, and the attack destroys the nation/state, then self defense necessarily fails.

On the other hand, an attack that destroyed the entire governmental, military, and economic infrastructure of the UK home islands but left some percent of the citizenship alive both there and abroad, is more likely and interesting.

In that case, a submarine commander might want to look for or even create a government in exile, and then use the threat (or limited actual use of) nuclear weapons to preempt further attacks or to convince the adversary to spend substantial funds repairing some of the damage.

As most surviving citizens would be suffering from radiation burns, blast damage, and in threat of starvation or other imminent threats, that seems to be a literal case of national survival where proportionality would be satisfied even in the destruction of an enemy city.

Another, more historical than legal point is that I doubt that 2(4) of the charter is an enforceable norm without nuclear deterrence. After all, the history of warfare before nuclear weapons shows a steady increase in deadliness and absolute casualty level. What previously took decades of brutal destruction could be achieved in days or weeks with massed artillery or conventional strategic bombing. But we kept fighting nevertheless.

On the other hand core developed states no longer attack each others urban centers after nuclear weapons. There are a few reasons:

1). the psychological terror of nuclear bombs. As it is somehow mythic in that a single bomb or weapon can destroy and permanently poison a city, people fear nuclear weapons more than equally deadly super conventional means (like a MOAB or a series of cluster bombs). It is an "all in" option.

2). Government self preservation. As a full scale nuclear attack or retaliation is likely to kill most, if not all, of a government's personnel (no bunker, even NORAD is truly secure against a modern icbm), so governments are presumably hesitant to take actions that result in their own (and their families) deaths.

3). There is a hard limit to nuclear power. Indeed, as long as you have enough nuclear weapons to survive and retaliate after even the most catastrophic full scale attack by the US or Russia, you are golden. After all, the potential loss of New York, D.C., and San Francisco (or Moscow, Saint Petersburg, and Novosibirsk) is so devastating that no policy would justify a substantial risk of this. That explains why North Korea is immune to US or Chinese military intervention. There would also be no Ukraine crisis today if they had their nuclear weapons.

Conventional power, on the other hand, has no real limit outside of economics and willpower: more tanks and planes always helps.

Where most of the worlds powerful states either 1). have nuclear weapons, or 2). are allied with nuclear powers/have nuclear capacity, then 2(4) works. Even if the whole world is against them, they can say "we are inviolable".

Without such weapons, states can use warfare to capture valuable resources, appease domestic political opinion, or otherwise advance interests without the threat of imminent destruction. Russia in the Crimea is the very proof of the necessity of deterrence to world peace.

Antonios Tzanakopoulos says

October 18, 2015

Both Dapo and I are very glad that this short piece continues to provoke debate. Many commentators here have raised the question of whether the (presumed) nuclear attack giving rise to the opening of the letter of last resort would lead to the destruction of the UK's international legal personality, or whether there should be no right of self-defence in cases where at least some UK citizens or overseas territories remain etc.

I think the whole premise of the letter of last resort is that an attack has been completed which was so devastating as to eliminate the whole UK chain of command and as to effectively destroy the state. Should that happen, then it is under domestic UK law that the state no longer exists, rather than under international law. Even if it retains its international legal personality (which is an interesting question), our argument is that the UK (the submarine commander being its organ) would not be acting lawfully in retaliating. This is because the lawful aim of self-defence is not to protect the (international) legal personality of the State, nor to retaliate on account of the few scattered nationals or overseas territories that have survived the nuclear holocaust, but either to stop an ongoing attack (too late) and/or to prevent an imminent one (again, rather too late).

So the premise is the destruction of the UK--only this leads to the opening of the letter of last resort (following the indicia which lead the submarine commander to irrebuttably presume such destruction). It is on the basis of this scenario that our analysis takes place. What constitutes such 'destruction' is for the UK to decide (by adopting the indicia related to the opening of the letter). After all, states may even commit suicide (and have done so in the past).