Nobuo Hayashi

Nobuo Hayashi. Photo: Peter Madai.

Meet your professor and his research

Nobuo Hayashi and International Operational Law

This former lawyer at the Prosecutor’s Office at the International Criminal Tribunal for the former Yugoslavia describes teaching as a participatory thought process, taking a fresh look at reality and sharpening one another’s mind.

Nobuo Hayashi is responsible for the master’s program International Operational Law, and he will follow along your side throughout the program as course convenor, instructor, supervisor and examiner.

Please tell us a bit about your background and your first academic steps...

"I grew up in Tokyo, but one year I spent as a high school exchange student in New Zealand awakened a desire to study further abroad and work internationally. It gave me completely new perspectives and, when I came back to Tokyo, the familiar environment felt a little suffocating. So, I applied for admission to a university in the United States where I started reading international relations and later international law in Washington D.C., and that’s the way it is."

When and why did you start your position at SEDU?

"I started working at SEDU in 2020. I came from the International Law and Policy Institute in Oslo where I worked as a senior advisor. I had been looking around for an opportunity to combine research and teaching in international law. I knew about the Centre for International and Operational Law at SEDU from before. When I saw the job advertisement, I knew that the environment here would give me the opportunity to develop. And if my experience and skills were to come in handy and meet the Centre’s needs, so much the better."

What is it about the SEDU academic environment that suits you?

"I specialise in the law of armed conflict (LOAC), international criminal law, the law on resort to armed force (jus ad bellum), international weapons law and general public international law, among other things. Given the subject-matters of my research and teaching, SEDU offers an unbeatable setting where theory meets practice. At a typical law faculty, you may be surrounded by similar minds speaking your occupational language. At SEDU, that same setup is complemented by the very people whose conduct LOAC is meant to guide in war."

What fascinates you about international operational law – and why should your students be equally fascinated?

"I am fascinated by the contradiction between conflict which embodies chaos and disorder, on the one hand, and how we have endeavoured since time immemorial to breathe order into this chaos with the help of law, on the other hand. This is a timeless dilemma, and LOAC becomes the obvious subject to study."

"There is also one aspect to law that many of us miss. We very often associate law with enforcement, and enforcement with punishment. In fact, this association is so strong that, for some, rules disqualify as law if their violators go unpunished. But law has a distinctly behaviour-shaping function. Very often, duty-bearers obey laws either willingly or even unknowingly. If that is (also) part of what makes law law, then it is possible that LOAC also possesses and discharges a behaviour-shaping function, a possibility well worth studying in my view."

In your current academic research, you have been working on two major themes. Please tell us about the first one:

"The first theme concerns the evolution in our strategic, ethical and legal understanding of honest battlefield errors over the past eight decades and in the future."

"In July 2023, I finished co-editing a multi-disciplinary anthology on this theme. Entitled Honest Errors? Combat Decision-Making 75 Years After the Hostage Case (Asser/Springer, September 2023), this volume critically examines the devastation of northern Norway during World War II and the 1948 Hostage trial held at Nuremberg. Lothar Rendulic, the German commander who ordered the region’s destruction and the forcible evacuation of all of its inhabitants in order to obstruct a feared Soviet invasion, faced war crimes charges for his decisions. Although, in the event, the Red Army never pursued retreating German forces across northern Norway, Rendulic pleaded how he had honestly believed military necessity justified his actions at the time. The judges agreed, noting that Rendulic’s conduct might have been faulty but not criminal. His acquittal gave rise to the so-called “Rendulic Rule”. Now widely considered a customary LOAC principle, this rule admonishes that battlefield decisions made in difficult circumstances with limited information not be second-guessed with the benefit of a hindsight."

"Our anthology contains chapters written by Scandinavia’s leading World War II historians. Their ground-breaking research into new archival material shows that Rendulic did not in fact consider the region’s wholesale devastation and total evacuation militarily necessary. This discovery also casts significant doubts about the Hostage judgment’s acumen and undercuts Rendulic’s acquittal. Our law chapters feature discussions by some of today’s foremost international lawyers from Australia and the US. They expose the Hostage trial’s shortcomings, reflect on the Rendulic Rule’s significance in modern LOAC, and sharpen our understanding of the so-called reasonable commander test and the mistake of fact defence in international criminal law. Our collection also features contributions in military strategy, legal philosophy and military ethics. These writings show how, despite the unprecedented advancements in military technology, human judgment, de-empathetic battlespace and institutional bias shape war-time decisional errors and collateral harm."

"The Hostage trial has been constantly on my mind since I began working on military necessity in the late 1990s. The idea of a multi-disciplinary anthology struck me as soon as I moved to Oslo in 2006. Nevertheless, it is only when my employment with SEDU began that a real opportunity to turn this idea into reality – requiring time, patience, and perseverance as it does – presented itself. So, I developed the project and set its parameters, recruited a co-editor and assembled an international team of historians, lawyers, strategists and moral philosophers, obtained a publication offer from Asser/Springer, and coordinated research, drafting and editing."

Why is this research significant, in your words?

"Because it compels us to revise received wisdom about the devastation of northern Norway, Rendulic’s acquittal at Nuremberg and the provenance of a key LOAC rule that is named after the general himself. Some of our findings also raise timeless issues, such as what it means for a harmful error to be both honest and reasonable in combat, and how the institutional biases of a military organisation can hinder its commanders’ ability to maintain honesty and reasonableness in their decisions. The advent of artificial intelligence (AI) into the battlefield may force us to re-imagine the very notion of honest errors in combat decision-making."

And what is your second research theme?

"My other research theme investigates the relationship between humanitarian imperatives, on the one hand, and LOAC’s development, application and adjudication, on the other. I am working on an extension of my monograph entitled Military Necessity: The Art, Morality and Law of War (Cambridge University Press, 2020). In that book, I hypothesised that some categorical LOAC rules (e.g., that all prisoners of war must be repatriated to their home country after the end of hostilities) may be put aside if humanitarian imperatives so demand (e.g., that prisoners of war may not be repatriated against their will). Also, though more contentiously, I theorised situations in which doing what black-letter rules permit (e.g., that you may kill, injure or capture enemy soldiers) may not be enough if it is against humanitarian imperatives (e.g., that you may not kill enemy soldiers if you can injure them, and you may not injure them if you can capture them). There is scholarship that offers some explanations for these scenarios. These explanations have so far been superficial and fragmented, however. A more robust and structured account of humanitarian imperatives in their interaction with LOAC has yet to emerge."

"I have been preparing a long article on this theme for some time now. It studies the end-phase of the Korean War in 1952-1953 when the United Nations Command (UNC) found itself struggling to determine the fate of tens of thousands of North Korean and Chinese prisoners of war held in its custody. Many of them agreed to return, but many others refused. The 1949 Third Geneva Convention on the treatment of prisoners of war came into force in 1950. That convention’s Article 118 stipulates in its first paragraph that “[p]risoners of war shall be released and repatriated without delay after the cessation of active hostilities”. No exception was added to this provision, partly because its drafters did not want to see the repetition of lengthy delays in the repatriation of Axis prisoners after World War II. Against this background, UNC authorities had to decide whether to follow Article 118 by repatriating all of its prisoners, forcibly if necessary, or to put the rule aside by allowing unwilling ones to stay in South Korea or settle elsewhere."

How would we handle similar dilemmas today, with modern international human rights laws?

"Today, we would have little difficulty resolving this dilemma by interpreting Article 118 in light of the prisoners’ human rights. Modern international human rights law protects persons against being sent to places where they risk persecution (it is called the principle of non-refoulement). The same protection applies to today’s refugees and asylum seekers. We readily agree that, in contemporary conflicts, prisoners of war enjoy non-refoulement. In the early to mid-1950s, however, the UNC did not have access to this principle because it had not come into existence yet. Instead, UNC commanders were left to choose between the law obligating prisoner repatriations without exception, on the one hand, and weighty – indeed, compelling – humanitarian grounds for non-repatriation in appropriate cases, on the other. In the event, they chose to follow the latter."

"This episode, I think, illustrates two important facts about the interplay between humanitarian imperatives and LOAC. First, this law, like any other body of law, cannot anticipate and legislate for all eventualities in advance. In particular, law cannot pre-empt future clashes with contradictory moral demands by simply adopting categorical rules. Second, it is possible that war-time humanitarian imperatives are an especially weighty kind of moral demands that can sometimes justify deviations from legal obligations. By exploring these normative interactions, my article endeavours to lay the groundwork for a theory of humanity and LOAC that ultimately accompanies the military necessity theory that I developed earlier."

"Elucidating the humanity-LOAC interplay is important because we need to acknowledge possibilities that, in some situations, one’s innate sense of humanity could – or even should – take precedence over strict compliance with the law. At the same time, this clarification must be done carefully, lest it give pretext to rampant law-distortion and breaking in the name of humanity."

What are some of the potential practical applications or implications of your research findings benefiting society?

"I see two concrete practical applications or implications that our Honest Errors anthology may have. To begin with, despite its creation more than twenty years ago, the International Criminal Court (ICC) has yet to hear a case that involves a defendant pleading a mistake of fact under Article 32(1) of its statute. That article does not specify what constitutes a valid mistake of fact. Our anthology argues that, in order to be a valid defence against international crimes charges, the defendant’s factual mistake ought to be both honest (i.e., subjectively honest as far as the defendant him- or herself is concerned) and reasonable (i.e., objectively reasonable as far as the impartial observer is concerned). These findings could very well shape the future direction of the ICC’s case law on mistake of fact defences."

"More broadly, over the past decade or so, the use of AI in combat decision-making has become the subject of lively debate. The matter encompasses a wide spectrum of AI involvement, ranging from the provision of rapid and large-scale data analysis in support of human decision-makers to the employment of lethal force decided fully autonomously and without human supervision. It is exceedingly likely that, even with full AI autonomy, battlefield decisions will remain prone to errors. Where such errors occasion harm, the honesty and reasonableness of these errors – human or otherwise – will feature prominently in culpability questions. Our anthology stands a reasonably good chance of making a tangible difference there."

"As regards humanity and LOAC, my findings may illuminate the manner in which commanders act on their humanitarian impulses during combat, state representatives formulate war-time rules, and lawyers (e.g., legal advisors, prosecutors, defence lawyers, judges) approach non-compliance with the law on account of humanity."

"First, humanity has occupied a contentious place in the waging of war. For some, moderation merely lengthens wars and exacerbates their net suffering as a result. Others insist that even warriors acknowledge intrinsic value in limiting specific harm and that shortening conflicts with brutality is not what maximises humanity. My research will reveal when and how soldiers recognise humanity amid warfighting and decide whether to conduct themselves accordingly."

"Second, it is often said that states weave a compromise between military necessity and humanity into the LOAC rules that they enact. What that means exactly nevertheless remains obscure. My work endeavours to shed original insights into the matter, at least from humanity’s point of view (I have already done so from military necessity’s point of view)."

"Third, if humanitarian imperatives in some situations were to justify non-conformity with LOAC, their conditions must be clearly laid out. I intend to articulate them in such a way that they are capable of sound interpretation and practical application by judicial officials."

"Hopefully, in the end, my research on honest errors and humanity will help clarify the moral and legal parameters within which society expects militaries to make key decisions."

Do you find that your research informs your teaching practices or vice versa?

"Thematically, my post-graduate teaching and my advanced research do inform each other. When I run a LOAC course at the master’s level, its module on fundamental principles typically considers some of the original insights gained through my military necessity and humanity work. Also, thanks to the Honest Errors anthology, I intend to introduce a new segment on mistake of fact as a defence in my international criminal law curriculum. Conversely, student feedback on “ideas-in-progress” tested through teaching sometimes directly influences my research outcome. This happened, for example, when a master’s students questioned my tentative position at the time that the lack of military necessity alone is sufficient to delegitimise any belligerent act. Prompted by her intervention, I reassessed my view on the matter and developed a diametrically contrary theory – that is, the mere lack of military necessity never delegitimises a belligerent act – in the end."

How would you say that your students benefit from getting in touch with research?

"I believe that the most important benefit students reap from getting in touch with research is the opportunity it gives them to engage critically with considered opinions. Acquainting themselves with the material, method and argument used for research would help them learn to think on their own, to express agreement where agreeable and disagreement where disagreeable without fear, and to clearly formulate their views on the matter."

Tell us about your approach on teaching:

"I want to teach because I find reasoning and tackling problems together with my students intellectually very satisfying. Teaching for me is, first and foremost, a platform where I test my own grasp of the subject and my ability to articulate ideas before an audience that may have dissimilar experiences and perspectives about our world."

"I treat teaching as a principled, uncompromising and participatory thought process in which my students and I confront our prejudices, question conventional wisdom, revisit our most elementary assumptions about organised society, and take a fresh look at reality. Teaching, then, is not about trying to bring students to my point of view. Rather, it is about sharpening one another’s mind."

"I would like to think that my students perceive me as an engaging, open-minded and intellectually honest instructor. I consider it my responsibility to equip students with the skills and confidence necessary not to take everything written in a legal instrument, said by a commentator or found in a ruling as given. What is essential, in my view, is for them to treat sources and authorities as the beginning, rather than the end, of their own intellectual journey. I endeavour to cultivate in my students a habit of critical thinking and methodological vigour. Nothing pleases me more than to see them develop and practice it in their professional pursuits."

Speaking of professional pursuits, you firmly believe in “blooming late”...

"Yes, in fact, I consider myself something of a late bloomer, too. I spent two years between high school and college, ten years at university before starting my first real job, nearly twenty years – on and off – finishing my doctorate, and more than forty-five years deciding to become a parent. Both of my current research projects are multi-year undertakings."

"Though admittedly frustrating at times, now I can honestly say I appreciate my life’s digressions. Taking time to ponder has helped me come to terms with the consequences of what I choose to do or choose not to do in the end, and I see value in what I do now that I would not have seen if I had done it twenty years earlier. I also feel how the years spent living shape the way I approach research and teaching. To me, the quality of one’s reasoning process matters more than the soundness of one’s conclusion."

"I am mindful that late blooming is not for everyone. All sorts of circumstances and inclinations can make it less attractive or even viable. Should one find him- or herself blooming late, however, I would encourage that person to embrace it. Take your time."

This is where you meet Nobuo Hayashi

Master’s programme International Operational Law

  • International Criminal Law (course convenor/instructor/examiner)
  • Master’s Thesis, International Operational Law (course convenor/instructor/supervisor/examiner)
  • International Operational Law in Operational Planning (examiner)

Free-standing courses

  • Responsibility in International Law (course convenor/instructor/examiner)
  • International Law of Military Operations (course convenor/instructor/supervisor/examiner)

What are some of your key contributions to the existing knowledge in your field and to your academic community?

"Besides the addition of my own findings to scholarship, I find it challenging to articulate the nature and extent of my contribution. I can nevertheless specify some potential examples."

"One involves a journal article I published on military necessity. It was extensively cited by prosecutors as the basis for devastation charges in their court submissions filed before the Extraordinary Chambers in the Courts of Cambodia."

"Another example concerns a passage from my military necessity monograph. When the ICC defined military necessity in one of its recent judgments, it used a formulation that looked suspiciously similar – in fact, virtually word for word – to the one I have developed. I was told by one of the lawyers involved in the judgment’s drafting that it was indeed taken from my work but the judgment simply did not have enough space to give it a proper citation (!)."

"The third example relates to a series of reflections I had publicised during the mid-2010s on the ethics of nuclear weapons and nuclear deterrence. During UN negotiations leading to the conference on the adoption of a Treaty on the Prohibition of Nuclear Weapons, several delegates quoted my writings in support of their positions."

"These examples may perhaps be taken as generating knowledge upon which members of my own international law community and our broader society then rely."

Have you encountered any unexpected or surprising results during your research?

"In fact, I have not encountered that many unexpected or surprising results during my research. Nevertheless, perhaps I can offer three anecdotes that somewhat resemble surprises. One is when I found a major flaw in my earlier opinion. As noted earlier, early in my military necessity research, I argued that the lack of military necessity is sufficient to delegitimise any belligerent act. Realising that this is illogical forced me to modify a substantial part of my overall view of military necessity. In the end, my entire theory came to rest on the idea that military necessity is normatively indifferent."

"The second episode is closely related to the first one. At the beginning of my military necessity research, I found myself struggling to pinpoint what exactly was wrong with the dominant theory I was criticising. I had already spotted its specific shortcomings, but it seemed to me that a more structural defect which would account for all of them was still lurking somewhere in the background, waiting to be discovered. As soon as I accepted military necessity’s normative indifference, however, I saw that not only the dominant theory I was opposing but also its rival theories all shared the same mistake. They treated an act’s military necessity as creating a normative demand to do it and an act’s lack of military necessity as creating a normative demand not to do it. This breakthrough enabled me to refine my criticisms of existing views on military necessity."

"The third anecdote concerns honest errors. From the outset, I was instinctively suspicious of Rendulic’s claim that he had considered northern Norway’s devastation imperatively demanded by military necessity. But my suspicion had primarily to do with his claim that he had believed a Soviet invasion likely and imminent. (I also addressed the matter in my Military Necessity monograph.) I was therefore unsure, though certainly hopeful, about what the Honest Errors project’s history experts would reveal through their archival research. Their findings were both more limited in scope and more damaging for Rendulic than I had anticipated. More limited in scope, because our historians confirmed that Rendulic did have good reason to fear multiple Soviet advances against his German army retreating across northern Norway. More damaging for Rendulic, however, because the contemporaneous documentary evidence shows a man unconvinced at the time that the region’s wholesale devastation or the forcible evacuation of its residents would be needed to counter the Soviet threats. This latter discovery has become a centrepiece of our anthology."

What, if anything, would you describe as hard or challenging within your field of research?

"Anyone researching LOAC – and, by extension, international law more generally – must contend with deep-seeded scepticism that exists around and within the discipline."

"Around the discipline are familiar voices that question its claim to be a field of law in the first place. Without a world legislature, a central law enforcement agency and a binding judiciary, international law simply stands powerless in the face of misbehaving superpowers and despots, does it not? What good does LOAC do if most of its violators go unpunished? Those of us who are active in LOAC/international law all have our own answers to these questions, of course, but the fact that we constantly find ourselves defending the very existence of our research subject can be daunting at times."

"Nor does it help that LOAC uses language and methodology that even trained lawyers sometimes find hard to follow. These and other substantial “barriers to entry” that surround LOAC cannot but undermine its relatability to broader audiences."

"Within LOAC, we often come across criticisms by those working closely with military personnel that researchers unfamiliar with the business of warfighting heap unrealistic expectations on the law by distorting its aims and contents. Conversely, LOAC researchers driven by humanitarian concerns doubt the ability of their military counterparts to restrain belligerent conduct and maximise victim protection. Crossovers from one camp to the other do occur, but they are relatively rare. It is also difficult to stay neutral and be taken seriously by both."

"In other words, we are studying a subject – i.e., man-made law that purports to control death and destruction in war – where high stakes, strong emotions and definite expectations often lead to disillusionment and acrimony. Continuing work in this field requires, in turn, awareness, modesty and fortitude."

What are your next steps – are there any particular areas you plan to explore further?

"The Rendulic anthology identifies several potential areas of further research. One concerns the very notion that a combat decision’s honest error should not be second-guessed with the benefit of a hindsight to the decider’s detriment. In other words, we should not fault a decision made reasonably and in good faith for a legitimate purpose (e.g., destroying property in order to slow expected enemy advances), even if it happens to generate an illegitimate outcome (e.g., property being needlessly destroyed in the absence of enemy advances). But what about a decision made unreasonably and/or in bad faith for an unsound purpose (e.g., confiscating private property in occupied territory in order to erect settlements), if it happens to generate a sound outcome (e.g., strengthening the defensive position of occupation forces)? Might such a decision be second-guessed with the benefit of a hindsight if it favours the decider? Although we seem instinctively averse to the idea, more may need to be said about whether and, if so, why we should feel that way."

"Another matter that shows promise involves the relationship between honest errors and AI-enhanced combat decisions. When such decisions commit harmful errors, what does it mean for relevant information to have been available to the human or non-human decision-maker? What counts as the information’s honest and reasonable assessment? When and how is accountability engaged for the harm caused? Today, LOAC’s AI-related debate is dominated by questions as to whether meaningful human control should be a mandatory component in the so-called lethal autonomous weapons systems and who should be held responsible when the use of such weapons systems results in LOAC violations. I fully expect that debate soon to broaden and encompass the occasioning of harmful errors. With the ground-laying work on honest errors already done, I should be strongly positioned to contribute."

"I have the feeling that my humanity and LOAC research will preoccupy me for the next few years. My aim is to author a book-length “sequel” to the work I have produced on military necessity and LOAC. And, if one does military necessity and humanity, one naturally has to do chivalry – the most obscure and the least well-understood of LOAC’s three normative foundations."

Extra / In short

Title: Associate Senior Lecturer

Current with/current research publication: Co-editor (with Carola Lingaas), Honest Errors? Combat Decision-Making 75 Years After the Hostage Case (Asser/Springer, September 2023)

My driving force as a researcher: Pursuing clarity of mind

Favourite author or novel: Kazuo Ishiguro, The Remains of the Day (Faber and Faber, 1989)

Last book read: Bjarnhild Tulloch, Terror in the Arctic: A True Story from Norway in World War II (Troubador Publishing, 2011)

Music: Medieval, romantic, neoclassical, instrumental jazz

Hidden talent: Finishing served food (I was raised not to leave anything uneaten on my plates)

I’m happy to discuss: Anything and everything, as long as the conversation is kept civil

In my spare time: Play with two small children (5 and 7 years)

Favourite motto/proverb: Il est quelquefois sans inconvénient de remettre à plus tard son travail – Le Petit Prince (Sometimes, there is no harm in putting off a piece of work until another day – The Little Prince).

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