The extraordinary history of the Special Operations Executive, SOE, is both heroic and tragic. Established by Winston Churchill in July 1940 with a mission to ‘Set Occupied Europe Ablaze’, the SOE operated in more than fifteen occupied countries, sabotaging and subverting the Axis war effort, and tying down many thousands of enemy troops. Sadly, many of those who performed this daring work behind enemy lines died during their service.
But the SOE was more than just an insurgent, guerrilla outfit. It was also part of a deterrent strategy: it sent the clearest message possible to Hitler that any invasion of the British Isles would be met by extremely determined resistance. The organisation was disbanded in January 1946, just as the nuclear age was beginning. It is an example of pre-nuclear deterrence.

As we seek to deter an array of non-nuclear threats, from incremental land-grabs in the South China Sea to the next Crimea-like annexation of a sovereign territory, there is much to study from the experience of the SOE. And some of the most important lessons apply in the field of ethics: where should the acceptable limits of modern deterrence be set, and what does that mean for the effectiveness of a deterrence strategy?

The Special Operations Executive had a famously controversial approach to ethics. It explicitly sanctioned what it euphemistically described as ‘ungentlemanly behaviour’. Churchill believed that, if Hitler dominated all of Europe, the rights and freedoms the West held dear would be no more. Hence, he authorised the SOE to fight outside some of the Geneva Conventions — for example by assassinating certain officials who posed no direct or immediate threat.

On one occasion, after the SOE helped assassinate SS-Obergruppenführer Reinhard Heydrich (the Nazi governor of occupied Prague, and chairman of the 1942 Wannsee Conference which planned the ‘Final Solution’), the Nazis responded by razing the two villages thought to have harboured the British-trained assassins in then-Czechoslovakia, Lidice and Lezaky, and killed some five thousand civilians. The Nazi savagery was not just a punishment, it was meant to deter similar acts of insurrection in the future.

Ethics matters for modern deterrence, and for several reasons. It’s not just that we want to know we’re doing the right thing. For a democracy, it’s important that we retain sufficient support for whatever we do; after all, the military remains subservient to civilian authority. And those two reasons together mean that, to be credible to those we are seeking to deter, our deterrence strategies need to be sufficiently ethical — or our adversaries will not take them seriously.

So, what is ethical deterrence? There’s no simple answer — again, for several reasons. Rules of engagement and international law offer clues, but they tend not to deal with deterrence directly. Even Just War theory, the long-established doctrine on when conflict is justified, is only partially relevant, because successful deterrence means avoiding war, not starting it.
For the West trying to establish where the ethical boundaries for modern deterrence should be — and any adversary trying to understand how we might respond to various provocations — there are four main traditions of thought on which to draw. Each of these approaches offers clues to what ethical deterrence might be.

The first approach to ethics is to make judgements according to their likely consequences. A choice which generates a good result is better than an alternative option which leads to something worse. How good and bad outcomes are defined is up for debate, and there are several models with radically different approaches on this. Utilitarianism, for example, advises us to do whatever maximises overall well-being, whereas a ‘do no harm’ approach might rule out options where one person suffers so a greater number of people benefit. A key question for the deterrence debate is whether it’s just the well-being of the home nation and allies that counts, or whether the adversary’s welfare is factored in, too.

But judging deterrence tactics solely by their results doesn’t automatically lead to the best outcome overall. To follow through on a deterrent is to impose cost, making things worse. This means that, if an adversary knows you only judge by consequences, they could start negotiations after every bad thing they do, to offer a ‘peace settlement’ in which their bad action can go unpunished. Following through on deterrence requires a certain bloody-mindedness; the credibility of deterrence depends on it, and bloody-mindedness is near the opposite of being governed by the consequences of our actions. So, the outcomes of our decisions are important when plotting deterrence, but they cannot be the only guide.

The second approach to ethics is to establish rules. Ethics based on guidelines for behaviour is as old as the Ten Commandments, and has a long heritage in Western thinking — perhaps the most famous exponent of this approach is the Prussian philosopher, Immanuel Kant, whose famous categorical imperative has been summarised as ‘Always act in such a way that you would be willing for it to become a general law that everyone else should do the same in the same situation.’

A rules-based approach is intrinsic to deterrence: when you are acting out reciprocity, you are following a rule of ‘tit-for-tat’; it is the spur to bloody-mindedness. Indeed, reciprocity is so deeply ingrained in almost all human cultures that it is easily a credible bedrock for a deterrence strategy.

Mutually agreed rules can lead to the most effective examples of deterrence. The absence of nuclear use since 1945 is primarily because of widely understood precepts, based on reciprocity. Norms against invading each other’s territory have deterred many land wars, too. And internationally-agreed rules in the maritime realm have stopped many incidents escalating into violence over several centuries. Establishing norms in space, information and cyber may be best route to deterring malfeasance in those new and more contested domains.

But, like consequence-based thinking, rules alone cannot suffice. Simple tit-for-tat can lead to an endless cycle of reciprocity — following rules of how to respond means a small and accidental transgression can spiral into a large-scale conflagration. That’s the problem Churchill confronted when he recognised that, for the SOE to defend the laws of war, those very laws would themselves have to be broken. And any clear set of rules invites an adversary to work around them. To both deter and be ethical, ethical deterrence needs more than just a set of rules.

The third Western tradition on ethics is all about virtue. This is about developing a set of characteristics, or a personality, which is intrinsically good. For the Ancient Greeks, this was a matter of judgement. Aristotle, for example, believed there was a golden mean which only experience could deliver, such as adopting the right amount of bravery, which is somewhere between cowardice and recklessness.

A virtue-based approach has uses in deterrence: it helps convince an adversary that you are the sort of person, or team, which follows through. There’s a reason why the military train so hard to perfect their warrior spirit — it doesn’t just make them good at fighting, but it helps convince an enemy that they’ll fight with determination, which may help scare the enemy away. The 2018 US National Defence Strategy didn’t make a virtue of ‘lethality’ by accident.

But making a virtue out of fighting is not, by itself, enough to deter effectively. It doesn’t tell you how much to deter, how you should fight back, or how to signal your intent. There will be times when virtue deters in exactly the wrong way — for example, making a response judicious when it should be swift. The right virtues will depend on the situation, which means virtues alone cannot determine the boundaries of ethical deterrence.

The fourth and final approach to ethics which prevails in the West is not really an ethical tradition at all. It is the set of views that ethics is somehow a mistake — a figment of our evolution, or a grandiose expression of nothing more than personal tastes. These sorts of approaches argue that the whole concept of a ‘right approach’ is flawed, and some of them are harder to dismiss than they might seem. If one of these views is right, then the notion that anything can really be ethical, including deterrence, is nonsense.

But even if that’s true, it doesn’t mean that ethical deterrence can be ignored. As long as people think ethics is important, then it will affect their behaviour, and ethics will matter automatically. And most people will accept that the very act of deterring something bad is itself ethical, whether their ideas of ethics make sense or not. It is one thing to think ethics are a mistake, but that doesn’t mean deterrence can’t be ethical.

So, all four of the approaches which dominate Western ethics offer something, but none of them offer a single, simple route to defining ethical deterrence. To be clear, that doesn’t mean ethical deterrence is impossible, it just makes it hard to define. And that, in turn, leads to some interesting conclusions.

First, it means your adversary will find it harder to predict your responses. Past behaviour will not always be a reliable guide, and an attack which was once below the threshold of a reaction may not remain so in the future. Prevailing culture can influence which approach comes to the fore. Ethical deterrence still allows for a flexible response.

Second, it means ethics can be used to underwrite a broad range of deterrent effects. By highlighting an outcome, or an action, or an attitude to be deterred, a strategist can use ethical concepts to make their deterrence posture more credible. This, in turn, encourages an adversary to understand and perhaps even adopt your approach to ethics, since this allows them, in turn, to deter more effectively, and because absolute ruthlessness will provoke a more motivated response.

Third, it means different part of the defence community can contribute to ethical deterrence in different ways. A war-fighter might emphasise their warrior spirit, and hence pursue a virtue-based approach. A lawyer or policy official may focus on rules, while a planner or strategist will look to outcomes. Three very different approaches, but all of them can be a central part of ethical deterrence.

And fourth, it means that ethical deterrence will be inherently complicated. Like the people and society ethical deterrence should defend, it will be mixed and diverse. In a way, this is reassuring. Just as we want deterrence to protect our people, we want it to safeguard our values. It can be comforting to realise both are similarly complex.

Murdering five thousand civilians to signal their will was an evil use of deterrence by the Nazis, while the assassination of Reinhard Heydrich was probably justified. That’s not just because of which side in the War performed those actions; it’s something about those actions themselves, the motivations for them, and the consequences to which they led. Hopefully, as ethical deterrence matures, we will establish a firm basis on which to be sure that Churchill’s deterrence strategy was right, and that Hitler’s was wrong.