‘The most humane of all weapons’: Discrimination, airpower, and precision doctrine

Abstract How did the norm of discrimination become the dominant yardstick to measure the ethics of US airpower? Conventional accounts suggest that as elites and publics embraced norms of discrimination, this pushed US air forces to adopt a precision doctrine, one that demands accurately striking military, and not civilian, targets. Relying on a pragmatic reading of norm contestation and settling, we suggest that conventional explanations have the causal story reversed: it was not the strengthening of the norm of discrimination that led US air forces to commit to precision bombing. It was the commitment to precision bombing that led to the strengthening of the norm of discrimination. As precision technology became available during the interwar period, air-force officers co-opted the language of discrimination to justify their emerging doctrine. This co-optation of the language of discrimination would not only settle these norms as the guiding ethics of airpower. It would also transform them, redefining these norms in ways that privileged the process of precision targeting, rather than the outcome of civilian harm.

range, with fewer civilian casualties' . 3 Likewise, in a 2014 speech at West Point, President Barack Obama defended the morality of US targeted killing operations, stating that 'in taking direct action we must uphold standards that reflect our values. That means taking strikes only when … there is no certainty -there is near certainty of no civilian casualties. ' 4 Norms prohibiting the targeting of civilians are codified in the USA's training doctrines and field manuals. They are embedded in complex targeting procedures, such as those that guided precision strikes in Afghanistan and Iraq. 5 They are realised in processes of 'weaponeering' , where technology is painstakingly matched to targets to achieve maximum efficiency and proportionality.
How did the norm of discrimination come to dominate US air doctrine? Traditionally, constructivist accounts have focused on processes of norm construction and constraint, arguing that as norms of discrimination strengthened, both elites and the general public demanded more discriminate and precise air campaigns. Before the Second World War, while there were legal prohibitions against bombing, these norms were not internalised, either by the military or by political elites, and thus there was 'only a very tenuous understanding that such actions were inappropriate' . 6 Only in the decades after the Second World War would it become unacceptable to deliberately target civilians from the air during war. 7 By the late 20th century, advances in precision technology provided the US air forces with the means to make their growing commitment to discrimination a reality. 8 We suggest that constructivists have missed a significant part of the normative story. Before the norm of discrimination could constrain airpower, debates about the norm had to settle. Actors had to accept that discrimination was the appropriate moral standard by which to judge the ethics of bombing doctrine. Using an original qualitative content analysis of airpower debates during the interwar period, we demonstrate that the link between norms of discrimination and air doctrine was not predetermined: it was not at all clear that the norm of discrimination could or should guide the use of airpower. We show instead that the interwar period was one of intense norm contestation, with actors arguing that norms of destruction and deterrence -not discrimination -were the right ethical benchmark: if airpower could credibly threaten to brutalise civilians, then it could either end wars quickly or deter them from starting in the first place. Such normative logic is certainly familiar, as it underlies ethical arguments about maintaining strategic nuclear arsenals today. 9 To explain how moral arguments settled around discrimination, we turn the conventional constructivist argument on its head. It was not the strengthening of the norm of discrimination that led US air forces to commit to precision bombing. It was the commitment to precision bombing that led to the settling of the norm of discrimination. In the 1920s and 1930s, US air forces struggled to create an airpower doctrine that would not overtly challenge the dominance of the US Army and Navy but would still allow them to pursue an autonomous, strategic doctrine. Fortuitous technological developments in bomber and bombsight technology opened the doors to the possibility of precision doctrine. As a result, airpower advocates could co-opt their opponents' moral reasoning, appealing to norms of discrimination to justify their emerging doctrine. This may sound like mere strategic rhetoric: having found an effective doctrine, airpower advocates conveniently deployed the language of discrimination, using this norm to give the extraordinarily destructive USAAF strategic bombing a 'patina of legitimacy' . 10 We draw on a pragmatic reading of norm contestation to demonstrate that this shift in the air force's moral reasoning was transformative in three ways. First, we argue that the air force's rhetorical co-optation was critical to normative settling. Once the air force embraced norms of discrimination, competing destructive and deterrence logics fell by the wayside. Second, we show how the air force's logics of action became oriented around norms of discrimination and, indeed, that this norm became tied to the US air force's sense of its autonomous identity and ontological security. 11 Even as the strategic bombing campaigns of the Second World War raged on, US officers believed that abandoning the logic of discrimination would undermine the identity of the service. This insecurity cemented the links between discrimination, precision, and air doctrine.
Finally, we argue that as the air force used discrimination to justify their precision doctrine, they changed the meaning of the norm of 'discrimination' . In a pragmatist approach, norms are not static 'things' that determine behaviour. They are configurations of discourse and practices, always in flux and prone to contestation and redefinition. The normative contestation of the interwar years not only settled but also transformed understandings of discrimination, converting it from a question of outcomes (did civilians die?), to a question of process (did actors adopt a precisionbombing doctrine?). This shift in normative understandings had critical permissive effects: it was not in abandoning but in following the logic of precision doctrine that the air force produced unfathomable civilian destruction in the Second World War. 12 Empirically, our argument recasts the interwar period and the Second World War as moments of critical development in moral understandings of airpower. Theoretically, a pragmatist reading further develops the literature on norm contestation. Constructivist scholars have recently produced rich accounts of contestation, where multiple actors compete to advance their preferred norms over the moral claims of others. 13 Yet much of this research focuses on normative change, rather than on settling. We demonstrate how a focus on practical action and moral reasoning illuminates how and when cycles of contestation end, who wins, and why.
The paper proceeds as follows. The next section provides an overview of the constructivist literature on the norm of discrimination and airpower, explaining why a shift away from norm construction and constraint to norm contestation and settling is in order. Following this, we outline the foundations of our pragmatist approach, detailing why military elites are critical to norm settlement, how and why processes of norm co-optation occur, and how this co-optation simultaneously settles and redefines the moral landscape. The empirical section of the paper traces interwar contestation over airpower. Here, while we rely on an established secondary literature, we also use primary resources, including a content analysis of contemporary debates in the media and archival evidence. We conclude with a discussion of contemporary debates about norms of discrimination 10 Tami Davis Biddle, Rhetoric and Reality in Air Warfare: The Evolution of British and American Ideas about Strategic and precision technology, including debates surrounding precision targeting and emerging arguments about the ethics of low-yield precision nuclear weapons. While we cannot discuss either subject in depth, we hope to identify these as important avenues of future research.

Norms of discrimination and the age of airpower
An expansive constructivist literature holds that norms are 'not alien to war' but 'are often crucial to determining how and when force is used in international politics' . 14 Much of this scholarship emphasises processes of norm construction and constraint: the primary puzzle, then, is explaining when, why, and how a norm of discrimination came to constrain military air doctrine, prohibiting air forces from intentionally targeting civilians during wartime. 15 While the norm of discrimination has a long history, its development has been neither linear nor teleological. A millennium before heavier-than-air flight was possible, there was already a clear norm proscribing the intentional harm of civilians during war. 16 In texts on European warfare, scholars trace the development of the norm of discrimination from Greek and Roman texts on the morality of killing, to St Augustine's writings on who may be justly killed in war, which laid the foundation of the Catholic Just War tradition, to the creation of a formal body of laws governing war in the nineteenth century. 17 As airpower's potential became clear, activists and elites attempted to impose legal restrictions to dampen its brutality. The Hague Conventions, for example, which were adopted in 1899 and revised in 1907, prohibited the 'bombardment of towns, villages, habitations or buildings which are not defended' . 18 This constructivist literature uniformly maintains that norms of discrimination failed to constrain US air doctrine during the Second World War, leading to 'a bombing spiral that ended in the virtual absence of any normative restraint' . 19 Only after the Second World War would the US air force come to accept the norm of discrimination and pursue a precision doctrine. For some, the strengthening of the norm led to increased constraint. While there might have been legal architecture in place during the interwar period, it remained ambiguous. It was unclear, for example, how to interpret which cities were 'defended' , and which were a legitimate target of aerial bombardment. Further attempts to clarify the legal relationship between discrimination and aerial bombing faltered. The World Disarmament Conference of 1932 attempted to abolish 'all bombardment from the air' but was summarily rejected. Negotiations at the Hague in 1922-3 proposed to prohibit the terror bombing of civilians, but this too was never adopted. In contrast, throughout the 20th century, norms of discrimination became more clearly defined and institutionalised, both in international law (for example, Article 52(2) of Protocol I (1977) of the Geneva Conventions) and in military doctrine itself. Others point to the importance of public opinion in increasing constraint. Outcry over US strategic bombing during the Korean and Vietnam Wars suggested a growing international belief that targeting civilians was immoral. 20 As precision technology developed, this finally made it possible for the US air force to adhere to norms of discrimination in practice. 21 and political change' , International Organization, 52:4 (1998), pp. 887-917. On the creation of norms of war, see e.g. R. Charli Carpenter, 'Vetting the advocacy agenda: Network centrality and the paradox of weapons norms' , International Organization Once the American military had access to precision technology, it 'created pressure to be good by removing a possible excuse for being bad' . 22 While constructivists focus on different causal mechanisms, they share a general narrative of how a strengthening norm created incentives for US air forces to embrace a discriminate, precision doctrine. This story has its critics. Realists deny the causal link between norms and military doctrine, and suggest that the US air force's preference for precision targeting is a matter of efficacy, not ethics. 23 Others, many from a more critical constructivist tradition, question whether normative constraints have actually made air doctrine more discriminate. Conway-Lanz argues that over time 'discrimination' became defined not in terms of outcomes -whether civilians were sparedbut in terms of intentions -whether civilians were purposefully targeted. So long as strikes were not purposefully aimed at civilians, non-combatant deaths were acceptable. Janina Dill shows that discrimination privileges a 'logic of efficiency' -the idea that any strike against a target of military and political significance is legitimate -over a 'logic of sufficiency' , which circumscribes strikes to those targets that directly affect combat between militaries. 24 And because norms of discrimination allow for 'collateral damage' , they have permissive effects, either sanctioning 'necessary' civilian deaths or the 'the destruction of essential infrastructure' . 25 Rather than question whether the norm of discrimination actually constrained air doctrine, we ask how this norm became the dominant ethical measurement of strategic bombing. In retrospect, it may appear obvious that norms of discrimination would come to constrain air forces, pushing them towards ever more precise doctrines and technology. Yet our analysis demonstrates that, during the 1920s and 1930s, actors were engaged in fierce normative contestation over which norms should guide the use of airpower, the outcome of which was not foreordained. In contrast, by the early 1930s, this normative debate settled: air-force elites no longer challenged the argument that airpower must be used discriminately to be ethical.
The interwar period and the Second World War were not moral deserts devoid of normative reasoning, but times of critical development in moral understandings of airpower. This case allows us to further develop the literature on norm contestation. These scholars have rightfully emphasised that norms, far from static, are consistently in flux and have used that insight to develop important theories of norm challenges and ideational change. To date, there is less work on contestation and norm settlement: how this contestation over norms ends, which norms emerge as dominant and why, and how this can reshape the normative landscape in the process.

Norm contestation and norm settlement: A pragmatist approach
We draw from pragmatic approaches to norm contestation and settling. 26 While conventional constructivist accounts often treat norms as structures, pragmatists see norms as embedded within practical action itself. Norms are 'carried along in those practices and the innumerable concrete 22  situations' in which that norm must be realised. 27 All practice, moreover, involves both instrumental and moral reasoning. Actors invoke norms to explain and justify their actions, both to themselves and to the world around them. Our core argument is that the US air force's co-optation of the norm of discrimination to justify their emerging precision doctrine led to norm settlement. Before 1935, air-force elites challenged the morality of discrimination, arguing instead that indiscriminate bombing was not only effective but moral. During the interwar period, these elites shifted their arguments, embracing the moral reasoning of their opponents. Much of the air force's shift was strategic, using the discourse of discrimination as a way to articulate the moral reasons behind their emerging precision doctrine. This rhetorical shift had significant effects, not only settling the norm of discrimination as the guiding ethics of airpower but also, in the process, changing the meaning of the norm itself. A pragmatist account of norm settling begins with actors positioned in what Dewey would call 'problem situations' with which they wrestle. 28 At times, both an actor's behaviour and the norms that justify it are fairly routinised, so much so that we can identify sets of habits, in which action and moral reasoning combine together in predictable ways. 29 At certain moments, however, habits become unsettled, and both the practice and the associated moral reasoning become more ambiguous and uncertain. These moments may seem revolutionary, even to contemporaries. Technological change can upend practices in their entirety. Simon Pratt shows how the coming of unarmed aerial vehicles unsettled norms against assassination. In other cases, habits are destabilised over time. As Sebastian Schmidt explains, leaders encountered a number of problems undercutting power projection at the beginning of the Cold War that challenged traditional practices of overseas basing and state sovereignty. 30 In their efforts to find and implement solutions, actors creatively use and rework the materials -including cultural materials, such as norms -in which they are embedded. Such efforts are likely to provoke significant contestation. When actors come to believe that their existing habits cannot address emerging problems, they will argue about which practices are most likely to produce effective solutions. This leads to normative contestation as well. Actors debate not only which solutions are most effective, but also which ones are most morally acceptable. Unsettled times thus set into motion competitive normative reasoning, where actors attempt to persuade or coerce each other into accepting their solutions as legitimate. It is through this competitive moral reasoningexplaining why a practice is legitimate -that norms become settled, as they become the dominant narrative of practical action.
The approach here thus treats norm settling as a practical process: actors, engaged in pragmatic action, locate solutions to emerging problems and offer reasons for why these solutions are moral. This raises three questions: who is likely to settle normative debates; why do these actors gravitate towards some norms and not others; and how does this shift in practice reshape the normative landscape?

Military elites and problem situations
Constructivists often treat the military as an object of normative constraints. Norms emerge from the agendas of non-governmental organisations, domestic human rights movements, civilian leaders, and sometimes the public at large. Militaries may accept or reject these norms governing the use of force, depending on their existing culture or interests, but they have very little agency in determining the rules of war. 31  and ordered by civilians' , and only after the norm strengthened was it gradually institutionalised by the military itself. 32 It may be that military elites have little involvement in initial norm construction. Charged with finding 'optimal' strategies, these elites are unlikely to embrace any rule that would potentially tie their hands. In contrast, pragmatists expect military elites to be critical agents during periods of norm contestation. As creators of military doctrine, these actors are intimately engaged with 'problem situations' , often tasked with finding appropriate solutions in unsettled times. Moreover, military elites' claims of expertise give them an advantage in arguing which norms may realistically be incorporated into military doctrine, and how best to do so. They have greater access to information about what technology is available to implement the norm, the training that will be necessary, and how observing the norm will affect efficacy. From a pragmatic perspective, then, there has been too much emphasis on how norms tie hands, and not enough on how militaries select which norms of warfare become dominant.

Practical change and norm co-optation
This brings us to the second theoretical question: why and how do actors settle on a particular norm? Why would military actors, in particular, prefer certain norms over others? Much of the existing literature draws a distinction between a 'logic of appropriateness' -choosing practices because of a belief that they are the morally 'right' ones -or a 'logic of consequences' , choosing those practices that are the most effective or efficient, and justifying them in whatever way makes them palatable. 33 In contrast, a pragmatic approach treats strategic and moral logics as inseparable. During unsettled moments, actors prefer certain policy solutions over others for any number of reasons. Some might choose practices to advance their own material interests. Militaries might prefer a particular doctrine because it advances its bureaucratic goals, garnering them more autonomy or resources. Others might be sincerely motivated by ethical concerns.
Whatever drives the choice, once they have settled on a practical solution, actors engage in normative co-optation, drawing on existing norms to justify their preferred doctrine. Normative co-optation is more often associated with civilian rather than military elites: these governors often face public scrutiny, and thus explaining why policies conform with existing norms is an integral part of the political process. 34 But military elites also rely on normative co-optation to advance their aims. In the United States, military elites must justify their doctrine to everyone from the president to Congress, the media, and the general public itself. Not surprisingly, military elites will most likely co-opt the norms that justify their preferred strategies. If a new doctrine becomes possible, these elites will change their normative argument as well.
This might sound not a pragmatic, but a rationalist and realist approach to norm contestation: military elites might claim that their strategy is moral, but in reality, they are merely pursuing what they see as an optimal strategy, and norms are window-dressing for military interests. Pragmatists reject this strategic/normative binary. Military actors, like all actors, operate within a thick normative environment and are thus constrained in what practical solutions are even conceivable. Perhaps more importantly, the process of normative co-optation -no matter how strategic -has significant causal effects: not only does it settle normative debates, ensuring a specific principle emerges as the overriding ethical benchmark, but normative co-optation can change the meaning of the norm itself.

Norm settlement: Dominance, identity, and the redefinition of norms
Once actors create a link between new practices and existing norms, this leads to 'normative settling' , as the norm becomes increasingly embedded and institutionalised in doctrine. When we say that norms become 'settled' , this is relative -norms are never fully fixed and uncontested. But once military actors link their practical solutions with existing norms, this should drive out alternative norms and dampen moral contestation. The process of norm settlement produces three significant effects. First, in contrast to periods of contestation, where multiple practices and normative justifications were seen as plausible, in more settled periods, the scope of what is considered acceptable practice should narrow considerably, and previously possible alternatives should fall by the wayside. Second, there should be evidence that actors' behaviour becomes oriented around the logics of the norm. As Pratt argues, for example, actors in the Obama administration did not believe they were violating norms against assassination when they engaged in targeted killings. Rather, they saw their action as guided by accepted norms of preventive warfare and self-defence. 35 While some might contend that the outcome is the same (an individual was targeted and killed off the battlefield), the moral logic is different -in one case, actors understand their actions as norm violations. In another, they see their behaviour as oriented towards an accepted moral logic. Indeed, this process can ultimately reshape not only the behaviour but the identities of the actors. From a pragmatist's perspective, contesting and settling problem situations is simultaneously a process of defining and shoring up the actor itself. 36 How norms settle thus shapes how actors protect their ontological security.
Finally, when norms become 'settled' , this leads to norm reconfiguration, transformations in the definition and understanding of the norm. In standard constructivist accounts, norm settling involves selecting among predefined norms. From a pragmatist perspective, it is the practical interpretation of the norm -not some abstract principle -that comes to dominate understandings of moral behaviour. Methodologically, this points to the problem in measuring normative settling as behavioural constraint. If pragmatists are right, if practical action changes the meaning of the norm, this suggests the connection between action and norms is always in flux. Indeed, as constructivists have long argued, norms can be redefined in ways to produce unanticipated permissive as well as constraining effects. 37 In sum, it is through pragmatic action that norms become settled. In the sections that follow, we illustrate how this process played out in debates over US airpower in the 1930s and 1940s. We demonstrate how the emergence of airpower in the early 20th century provoked intense contestation in the United States (and globally) over how airpower could and should be deployed during war. We then show how, as the technology of precision emerged, air-force advocates coopted norms of discrimination to justify their doctrine. We conclude by tracing the process of normative settling, analysing how debates in the United States about the morality of airpower narrowed; how the logics of the US strategic air campaign, and even the identity of the air force itself, became tied to norms of discrimination; and how the definition of discrimination shifted to revolve around practices of precision.
The 'problem situation': Norm contestation over airpower, discrimination, and the future of war Observers had long predicted that there would come a time when airpower would bring a 'revolution in the art of war' . 38  unclear about the new instrument's role in future conflicts. Debates raged about whether airpower should simply augment traditional instruments of war-fighting, or whether it had a revolutionary strategic and autonomous role on the battlefield. Not surprisingly, proponents of the former position included Army and Navy officers eager to protect their resources and prestige. Throughout the interwar period, for example, the army fought to maintain control over its air arm, helped by a conservative War Department which stressed aviation's 'role in supporting conventional forces' . Airpower was useful in providing close air support, reconnaissance, and communication, but it was not an 'independent agent of victory' . 39 The Navy advanced a doctrine where airpower would assist in coastal defence by complementing, but certainly not replacing, their favourite instrument of the battleship. Airpower enthusiasts, in contrast, argued that airpower should have an autonomous and strategic role in future conflicts. In the wake of the First World War, the Army air forces began to claim that the aeroplane, not the battleship, lay at the core of American defence against foreign enemies. Bombers could patrol American coastlines and sink incoming fleets. Some went so far as to say that the air force now constituted the nation's first line of defence against an attack on the continent and argued that 'surface navies … are rapidly losing their importance' . 40 All of this challenged the Navy's status as the primary guardian of US security from threats abroad. 41 Offensively, airpower could play an even more important role. It was essential the United States stand up an independent service capable of conducting 'strategic operations against enemy aircraft and enemy material, at a distance from the actual line' . 42 Airpower not only unsettled military doctrine. It also upended norms surrounding the use of force. To demonstrate norm contention, we conducted a content analysis of debates over the use of airpower, spanning from 1922 to 1935. We used computer-assisted qualitative data analysis, coding 79 articles and editorials from the New York Times, as well as international law journals. 43 We focused on coding speakers' moral arguments, identifying how actors were justifying their position on airpower. While an editorial or law journal article might have one speaker and argument, a news article might contain several speakers making different arguments. These works were double coded by the authors and a research assistant. We complemented this more formal qualitative work with additional analysis of transcripts of forums on the use of airpower and the lectures and public writings of airpower advocates and critics.
We found that from 1925 to 1935, moral arguments were almost equally grouped around two contradictory positions. Those who argued that airpower should be limited or even banned outright invoked norms of discrimination to justify their position. Newton Baker, Secretary of War during the First World War, who in 1935 would chair a board that circumscribed the autonomy of the air services, argued that bombing attacks on civilians 'constituted an abandonment of the time-honored practice among civilized people of restricting bombardment to fortified places' . 44 Navy and Army officers, determined to keep the air forces in a subordinate role, were also vocal in their appeals to norms of discrimination to justify their positions. the American population would not stand for the brutality of air-force doctrine: 'If the "people of the United States" had seriously considered this question of international morality, they would reject the idea of strategic bombing, and in so doing would abolish the "principal excuse for an independent air service"' . 47 In contrast, those advocating for a strategic role for airpower challenged the claim that airpower must be discriminate to be ethical. Instead, they relied on norms of deterrence and destruction to justify the use of strategic airpower. Here, the moral argument was that strategic aerial bombardment was ethical, not because it avoided targeting civilians but because it did so: brutalising civilians would shorten wars and make them more humane. 48 Certainly no one wanted to revisit the horrors of the First World War, with its trench warfare and devastating naval blockades. In the United States, William 'Billy' Mitchell, the senior air commander of the First World War, was the most visible proponent of this normative position. For Mitchell, modern warfare's centre of gravity was found in the civilian population; break civilian morale, and the entire foundation of a state's economy and war-fighting capability would collapse. For this reason, 'it may be necessary to intimidate the civilian population in a certain area to force them to discontinue something which is having a direct bearing on the outcome of the conflict' . 49 While seemingly brutal, doing so would cause a quick collapse of the opponent, shortening the conflict and preventing another war of attrition.
Mitchell may have been the most vocal advocate of the ethics of destruction, but his moral reasoning was not a fringe position. In the interwar period, the notion that targeting civilians was a moral good pervaded airpower advocates' arguments. This moral reasoning formed the core of a 'progressive' school of airpower, who argued technology could save humankind from the horrors of the First World War. 50 Arguments expounding the virtues of punishing civilians were incorporated into the 1926 Tactical School text Employment of Combined Air Force, which argued that targeting the whole population of a country 'was a means of achieving the military objective with the least possible cost' . 51 In legal journals, airpower advocates argued that civilians were already suffering during wars of attrition, as long-term mobilisation, naval embargoes, and conscription slowly decimated the social and economic fabric of the country. 52 Public commentators adopted this moral reasoning as well, echoing airpower advocates' claims that targeting civilians from the air could lead to shorter, humane wars. 'Trench warfare' , one New York Times feature argued, 'is the most static and futile thing conceivable. ' 53 Better to use all of the technological advances available -including aerial bombardment of civilians -to shorten the war. A 1924 op-ed in the New York Times advocated aerial gas attacks on cities, noting that 'a sudden strike, within a few hours of the declaration of war … would have a startling effect on morale' . 54 In 1936, Hanson Baldwin warned that 'no matter how war is started, it is certain that bombing raids against cities and civilians will be an integral part of future conflicts' , but that these first clashes may be decisive. 55 Others deployed Mitchell's moral reasoning, but with a 'deterrent' twist: civilian punishment, even if it failed to shorten wars, was ethical because it might make wars themselves obsolete. Once civilians understood that it was they, and not their armies, that would be the target of attack, 'the sooner they would appreciate the folly and futility of war' . 56  moreover, was argued to be the most consistent with an American grand strategy, one that aimed to stay clear of Europe's conflicts. In this period of contestation, then, debates over airpower broke down into two diametrically opposed positions. It was not clear to contemporaries that discrimination could or should be the ethical standard for the use of airpower, or if deterrence and destruction would rule the day. Observers recognised this moral ambiguity throughout the analysed texts. As one Army air corps captain observed in 1925, 'there is no vast body of aerial law to which we can resort for guiding rules, precedents, and principles' . 57 A legal expert on airpower maintained that there were a 'multiplicity of laws' that could apply to the conduct of air wars. All of this left the normative debate over strategic bombing, as one contemporary observer put it, in 'a state of baffling chaos and confusion which makes it almost impossible to say what in any given situation the rule really is' . 58

US air forces and norm co-optation: Precision technology and the turn to discrimination
It was elites within the US army air forces that ultimately ensured that norm contestation settled on discrimination. During the 1930s, the emergence of precision technology -the B-17 bomber equipped with the Norden bombsight -allowed the air forces to articulate a strategic precision doctrine that promised to deliver military effectiveness while observing norms of non-combatant immunity. Throughout this period, the air force behaved as a pragmatic actor, using the technological resources at hand to create a doctrine that would give them bureaucratic autonomy. In linking nascent precision technology and doctrine with the moral reasoning of discrimination, these elites ultimately ensured that discrimination would become the normative standard by which their use of airpower would be judged.
The actors responsible for settling were the officers at the Air Corps Tactical School (ACTS), located in Maxwell Field, Alabama, which offered a nine-month course on airpower theory and practice to the Air Corps' top mid-level officers. 59 The influence of ACTS on air-force doctrine cannot be overstated. A core group of officers at ACTS, including Harold 'Hap' Arnold, Hayward Hansell, Carl Spaatz, and Ira Eaker, would become known as the 'bomber mafia' , the creators of the US airpower doctrine that would dominate the Second World War. During the 1930s, these officers at ACTS were wrestling with a significant doctrinal problem. Like their predecessors, officers at ACTS were debating how airpower could be used most effectively against an opponent. But they did so while facing increased bureaucratic constraints on their mission. While the air force had been allowed to establish a more centralised command structure, a series of decisions had made it clear that any air-force doctrine must directly support US ground forces.
In the face of these constraints, instructors at ACTS began to articulate a precision-oriented 'industrial fabric' theory of strategic airpower. In this vision, the air force would support the US army by targeting an opponent's 'vital centers' -oil, transportation hubs, ball-bearing plants -that would cripple the entire 'industrial fabric' of wartime. 60 This precision-targeting doctrine would allow the air force considerable strategic autonomy, while still ensuring airpower operated in service to ground forces. Initially, the industrial-fabric doctrine existed only as a theory, and only one among many. Although we find evidence of the industrial-fabric doctrine appearing in ACTS lectures as early as the early 1930s, it was not dominant and continued to compete with other ideas about how to best use American airpower. It took technological innovations -in particular, the invention of a bomber capable of significant range and altitude (the B-17 Flying Fortress) that could be equipped with relatively sophisticated bombsight technology (the Sperry and the Norden Bombsight) -to change the debate about airpower. It is important to note that this technology developed independently of air-force doctrine. As one historian explains, as long as the Air Corps' mission was still being debated, 'its demands for bombsights were also unclear' . 62 Indeed, a memo from the Air Corps chief 's office insisted that 'sights are not an integral part of the airplane' . 63 Ironically, it was the Navy's efforts that led to the development of the Norden bombsight: the service was eager for the capacity to target an opponent's battleships and defend the US coast. But once the Norden bombsight existed, it enabled the air corps to fully embrace the principles of precision doctrine. With the technology for precision bombing now in hand, by 1934, ACTS texts began to place its industrial-fabric theory front and centre. ACTS instructors focused on identifying which nodes must be targeted to weaken an opponent's ability to wage war. The school analysed US cities to determine the urban vulnerabilities of their opponents, such as power grids and transportation infrastructure. They analysed their own supply lines to think about how they might cripple an opposing air force.
Along with this shift in practical doctrine came the moral reasoning of discrimination. Having embraced a precision bombing doctrine, air-force officers began to co-opt the very language of discrimination that opponents had used to criticise strategic bombing. This may sound like utilitarian logic at its core, with norms of discrimination serving as mere lip service to national or even bureaucratic interests. It is certainly true that many air-corps officers were motivated more by precision's effectiveness than its morality. 64 In 1934, Major Harold George, then an instructor at ACTS, testified on air-force doctrine before the Federal Aviation Commission, arguing that military targets were superior to civilian populations, 'not because of the fact that it might violate some precept of humanity' , but because hitting the military-industrial network would produce better results. 65 Other prominent members among the air-force elite, such as Spaatz and Hansell, expressed a sincere commitment to reducing civilian casualties. Some, such as Major General Jimmy Doolittle, appeared to vacillate in their own beliefs.
But in a pragmatist model, why it is that actors appeal to certain norms of discrimination is not central to outcomes. Regardless of intentions, the process of linking a precision doctrine with existing norms of discrimination had significant effects: it settled debates about which norms, if any, should govern aerial bombardment; it oriented the air force's behaviour and even identity; and it reconfigured discrimination to be defined in terms of processes rather than outcomes.

The dominance of discrimination
The Army air corps' use of the norm of discrimination to justify their doctrine settled ongoing debates about what constituted the ethical use of American airpower even before the Second World War. Before the turn to precision doctrine, course 'texts, lectures, and doctrinal papers smacked of the ideas of Billy Mitchell' . 66 As precision doctrine began to take hold, so too did the norm of discrimination come to dominate. A 1934 text noted that while some other countries might target cities, this would incite the 'wrath of world opinion' as it was an 'undeniable fact that the consensus 62 Timothy Moy, War Machines: Transforming Technologies in the US Military, 1920-1940 (College Station: Texas A&M of world opinion is opposed to such employment of air power' . 67 Another text stated that the 'direct attack of the civil populace … is rejected as an air objective due to humanitarian calculations' . 68 On the eve of the Second World War, ACTS lecturers were explicitly contrasting their new precision doctrine, with discrimination as its moral reasoning, with normative arguments about destruction and deterrence. In a 1939 lecture, one officer explained that attacking the national economic structure excluded 'bombing and gassing the civilian populations' , although the Europeans may still hold to these practices. Likewise, Hansell explained in 1938, there were 'two general methods by which air forces might exert conclusive action through warfare (a) by disrupting the life of the civil populace … and hence causing such suffering as to make the civil populace prefer the acceptance of peace (b) by paralyzing the industrial machinery' . 69 In adopting the second approach, the US air force held to norms of discrimination and rejected ethics of destruction and deterrence logic. In his lecture 'The Aim in War' , Hansell declared that while airpower may seek to break the will of enemies, 'let us make it emphatically clear that that does not mean the indiscriminate bombing of women and children' . 70 Precision was key to the air corps' plan, as 'no amount of skill or proficiency in other ways can compensate for failure to deliver the bombs with sufficient accuracy' . 71 Arnold went as far as to argue that the bomber 'when used with the proper degree of understanding, becomes, in effect, the most humane of all weapons' . 72 Normative settling occurred in public forums as well. Appeals to norms of destruction and deterrence in the media disappeared almost entirely and were replaced by a narrative that US airpower was uniquely discriminate. The press reported that American strategic bombing was 'so accurate that industrial sections of cities could be wiped out, area by area' without needlessly killing civilians. 73 Reporting on bombers in training, the press applauded the air corps for their commitment to discrimination. They described tests where bombers 'missed every residential section and hospital and knocked docks, factories and ships into smithereens. It was a raid of destruction, not of vengeance, a raid to show the way in which bombardiers are being trained enables them to plant their stuff where it will do the most to win the war' . 74 At the New York Times, Baldwin no longer argued that strategic bombing would deliver punishing blows against civilians, but that Americans would preserve non-combatant immunity through the 'precision bombing of specific targets' . 75 The air force's emphasis on norms of discrimination persisted throughout the Second World War. As strategic bombing campaigns intensified, air-force commanders insisted that they were following the norm of discrimination, even as civilian casualties mounted. As Spaatz resisted area bombing in Berlin, he suggested that the USAAF could instead aim at 'targets for attack of military importance' . 76 On the day of the Berlin raids, Doolittle 'had his crews target transportation facilities and government areas in keeping with his concept of how Americans should bomb' . 77 After the firebombing of Dresden, military elites scrambled to demonstrate that their intention was to hit military targets. Secretary of War Henry Stimson responded to charges of terror bombing by requesting that 'the City be thoroughly photographed to establish that our objectives were, as usual, military in character' . 78 While the Germans might have suffered, the USAAF's aims and processes remained consistent with ethical action.
In Japan, a mixture of retribution and racism made civilian suffering more palatable to the American public. 79 Yet even here, the air force insisted that 'the object of these attacks was not to bomb indiscriminately civilian populations. The object was to destroy the industrial and strategic targets concentrated in the urban areas of these four cities. ' 80 Newspapers echoed this emphasis on 'industrial targeting' , noting that the incendiary campaigns over Japan's urban areas were aimed at specific targets. The New York Times, for example, remarked that the firebombed cities contained 'most of Japan's war potential' . 81 Reporters praised examples of continued 'precision bombing' . Whatever the effects of incendiary bombing, then, the ethics were sound. It might be the case that the B-29s could 'wipe out Tokyo altogether' , 82 but the USAAF objective, as in Germany, was 'to cripple the enemy's war potential and soften up his defenses against invasion' . 83 In short, even before the war began, the American discourse around strategic bombing had settled on a norm of discrimination. What had been at one time a grand philosophical argument about the morality of airpower now became an instrumental disagreement about 'techniques and proportions of the air war' . 84 Moreover, the normative consensus that developed around non-combatant immunity was unique to the US air force. 85 Before the war, British RAF officers argued about the morality of attacking civilians. After the war began, indiscriminate attacks on civilians were justified as necessary acts of retribution against German aggression. 86 In contrast, as the allies waged air campaigns against Germany in 1943, Arnold would denounce terror bombing as 'abhorrent to our humanity, our sense of decency' . 87

Discrimination, logics of action, and ontological security
Some would of course argue that none of this rhetoric mattered. American bombing campaigns in Germany and Japan hardly seem consistent with norms of discrimination. In Germany, an estimated 600,000 died in strategic bombing campaigns conducted by the RAF and USAAF. A million more were seriously injured, and millions more were forced from their homes. 88 From January 1944 to August 1945, the USAAF dropped 160,000 tons of bombs -incendiaries and high explosiveson Japanese cities. The US Strategic Bombing Survey estimates that 333,000 people died, including 100,000 killed in a single night in the firebombing of Tokyo in March of 1945, and another 120,000 killed in the atomic bombings of Hiroshima and Nagasaki. 89 Indeed, among International Relations scholars, there is near-consensus that norms of discrimination played little role in the air campaigns of the Second World War. Whatever appeals were made to norms of discrimination were merely window-dressing. 78  Norms of discrimination did little to prevent death and destruction, but private correspondence among air-force commanders suggests that they saw the use of airpower as oriented around discriminate doctrine and, indeed, that they believed that adhering to norms of discrimination had become essential to preserving the air force's autonomy and identity after the war's end. These commanders' concerns about future air-force identity are particularly surprising. As the war went on, there was little evidence that the American public was interested in punishing the air force for its destruction. On the contrary, it seemed that Americans were increasingly willing to accept civilian deaths, even deliberate ones, so long as they would shorten the war. A 1942 editorial in Time magazine called for an all-out assault against Germany that would target '31 key cities and their suburbs. These cities comprise the core of the German war production. ' 90 Racism only increased Americans' willingness to punish Japan, where 'Japan's essential industrial production is concentrated in a very few [cities] … bombing these population centers is the simplest way to strike at Japan's civilian morale and cripple her vital industry and communications' . 91 But, as pragmatists would expect, engaging in moral arguments had altered the air force's understanding of their ontological security: they had come to view their own survival as an organisation as dependent on their orientation towards the norm of discrimination. Nowhere is this more apparent than in debates among air-force commanders over coordination with the RAF in German bombing campaigns. As scholars have long noted, on paper at least, British and American air forces adopted different approaches to strategic bombing: while the British embraced nighttime 'area bombing' , the United States adhered to precision doctrine, which mandated daytime high-altitude operations. 92 Much of the existing literature aims to demonstrate that there was little difference between the outcomes of these doctrines, because both had devastating effects on civilian populations. 93 But not only did the US air forces see their doctrine as incompatible with the British, their orientation towards discrimination created significant obstacles to allied cooperation. In January 1941, for example, British and American air commanders attempted to produce a coordinated plan for the strategic bombing of Germany. In August of 1941, the British presented their vision of strategic bombing to the Americans and requested a formal reply. The 'principal objection made by American military conferees was to the British policy of "area" or "saturation" bombing of civilian population centers' . 94 In their reply, 'they took exception to the bombing objectives, decrying the apparent emphasis on attack upon civilian morale' . 95 This reluctance to adopt Britain's area-bombing doctrine continued throughout the war. Concerns that cooperating too closely with the RAF would undermine the US air force's autonomous identity, its ontological security as an ethical service, pervade the correspondence among American air-force commanders. When the Combined Bomber Offensive asked the USAAF to target cities, officers mounted fierce resistance, arguing that participating in areabombing campaigns would lead to public blowback. As Spaatz wrote to Arnold after receiving the details of Operation Thunderclap, the bombing of Berlin, 'there is no doubt in my mind that the RAF want very much to have the U.S. Air Forces tarred with the morale bombing aftermath which we feel will be terrific' . 96  with a view to breaking civil morale, such a plan as this is probably the way to do it. I personally, however, have become completely convinced that … we should never allow the history of this war to convict us of throwing the strategic bomber at the man on the street' . 97 Similarly, in summer of 1944, as the British began planning for Thunderclap, the Americans remained defiant. One commander wrote that the plan was nothing but a 'combination of retaliation and intimidation' and that the USAAF would suffer from the RAF's 'baby killing schemes' . 98 These debates did not simply exist in private correspondence. In Europe, the USAAF continued to adopt daylight precision-bombing campaigns, even though this doctrine proved costly, both in terms of lives and treasure. Daylight precision raids proved disastrous for the USAAF: even at high altitudes, daylight bombing left the USAAF a target of increasing German fighter defences. At Schweinfurt, for example, 198 of the 291 bombers dispatched were shot down or damaged; 593 airmen were lost in the raid. Even as they adopted non-visual bombing -allowing bombers to use weather for cover and fly at high altitude -the daylight arena, Overy writes, remained 'among the harshest of the air war' . 99 A March 1944 POINTBLANK raid cost the USAAF 10% of the raid's force. In April of that year, the United States lost a total of 422 heavy bombers, almost 25% of its force. Precision bombing forced the USAAF to absorb heavier costs than the British. But the service, as Anderson wrote to Arnold, believed the 'greater risks are justified' and 'high costs are to be expected' . 100 Arguably, had the USAAF embraced the British doctrine of area bombing outright, it could have lowered these costs and risks. Fewer airmen would have died. There would have been no need for investment in the costly Norden bombsight, or in planes designed to fly at higher and higher altitudes. We cannot, in essence, understand these strategic decisions without taking seriously the air force's settling on norms of discrimination as the benchmark of ethical behaviour.

Norm reconfiguration: Discrimination as precision
By tying the moral reasoning of discrimination to precision doctrine, the air force transformed how actors understood and put into practice the norm of discrimination. To 'discriminate' between military targets and civilian populations now became a question of whether actors had adopted precision processes -that is to say, did the air force use precision technology and targeting -rather than outcomes (were civilians protected from harm).
Thinking of 'discrimination' as 'accurately striking military targets' is only one way to define the norm of discrimination. As Dill argues, for example, discrimination can also be defined as a doctrine of sufficiency, where only assets that have a direct effect on military outcomes are legitimate targets, and Conway-Lanz contends that whether force is used discriminately is often assessed through intentions rather than outcomes. 101 Our focus on precision processes does not undermine these arguments about intentions but adds another layer as to what types of doctrine will be seen as moral. Moreover, this question of what discrimination 'means' is not simply an academic debate. During the interwar period, advocates proposed myriad ways to ensure discrimination. States could adopt a 'no cities' approach to diminishing civilian casualties, for example. If that seems hopelessly naive, others argued that close air support, which would have brought the air forces back behind the front lines, was both a more ethical and effective approach to airpower. 102 In marrying discrimination to precision practices, the norm itself took on a distinct meaning, one that privileged the process of targeting over the outcome of civilian harm. This transformation in the meaning of discrimination is important to understanding the bombing practices of the Second World War. Theoretically, one could deliberately and effectively engage in precision targeting but still use a weapon with substantial yield, leading to significant civilian casualties. Likewise, attempting to maximise the chance that a target is destroyed by using multiple precision strikes technically fits the definition of 'discrimination' but also increases civilian destruction. For example, airmen recognised early on that the large centre error probable (CEP) of Second World War technology meant that ensuring the destruction of a military target required increasing the number of 'precise' hits on that target, which amounted, in practice, to saturation bombing. Arnold argued that destroying a single target would mean organising B-17 bombers into forty bomber formations that would 'drop their bombs in a single salvo' . 103 In 1941, using canal locks as a hypothetical target, another air-force commander argued that pinpoint bombing could work, but it would require 'more than 120 bombers dropping over 1000 bombs to get the nine hits to do the job' . 104 These calculations proved more than theoretical; they were the foundation for the overwhelming bombing operations in Europe and Japan -despite appearances, massive bombing formations were not meant to maximise destruction, but rather maximise accuracy. The effects on the ground, however, were the same as terror bombing, but the moral reasoning of discrimination -as defined by precision practices -still applied.
Likewise, defining discrimination in terms of precision targeting processes meant that even practices like radar bombing might constitute ethical behaviour. Scholars point to radar bombing as evidence that the United States abandoned precision principles in both Europe and Japan, and proved willing to accept the civilian casualties associated with radar targeting. 105 But the USAAF did not see its radar bombing this way: while they admitted that radar bombing was likely to lead to increased civilian casualties, they also argued that radar would allow them to distinguish military targets from civilian ones and thus ensure that military targets were given priority even in the fog of war. 106 But on the ground, these precision targeting practices led to increased civilian punishment. With radar in hand, the USAAF became more willing to bomb in adverse weather conditions, rather than wait for clear skies and visual targeting. The pursuit of 'precision' also meant the air force now prioritised targets that could be identified by the H2X radar system, notably those larger 'transportation' targets -railway centres and marshalling yards that often abutted urban populations. 107 Scholars often assume that normatively driven outcomes will be more moral than instrumental ones. For this reason, they dismiss out of hand the idea that US strategic bombing in the Second World War contained any normative reasoning -and certainly not the moral reasoning of discrimination. To be clear, there is no denying the brutality of US air campaigns, and the devastating impact this had on civilian populations. We are not arguing these campaigns were moral. But as counterintuitive as it may seem, US air doctrine was still oriented around the logics -if not the outcomes -of discrimination. The US air force's focus on discrimination produced perverse 'permissive effects' . So long as the air campaign was seen as oriented around the logic of discrimination, civilian bombardment became acceptable.

Conclusion
We have argued that it was not inevitable that norms of discrimination would guide the use of airpower. During the interwar period, there were other available moral justifications for the use of airpower, most notably appeals to destruction and deterrence. It was only as precision technology became available that air-force officers turned to the language of discrimination to justify their emerging doctrine. Their normative co-optation was pragmatic, a means to articulate the ethics of their emerging doctrine. For some, the moral reasoning was sincere, articulated by airpower advocates who truly saw airpower as a way to avoid the horrors of the First World War. For others, the ends were more strategic -appealing to norms of discrimination was a means to secure the country's investment in air power and a strong autonomous air force. Whatever the motivations, this turn to the norm of discrimination would have a profound effect on the subsequent development of military doctrine. It would not only centre norms of discrimination in airpower but also transform them, redefining these norms to centre the process of precision targeting, rather than the outcome of civilian harm.
Understanding how the ethics of airpower settled around norms of discrimination is not only of historical interest. Throughout the paper, we have pointed out how theorising settling in this case contributes to broader understandings of norm contestation. Beyond this, unpacking the link between discrimination and precision practices sheds light on contemporary debates about airpower. For example, in both Iraq and Syria, the increased ability to hit military targets with precision has made the use of airpower in urban areas more likely, often with devastating results. As one major reported of the Battle of Mosul, 'when precision strikes do not achieve their desired effect within the first strike and threats reposition to another structure, they expand the potential for collateral damage and civilian casualties' . Targeted leadership moves 'from structure to structure, trailed by precision strikes, leaving a swath of death and destruction in their wake' . 108 Perhaps more disconcertingly, a pragmatic reading points to the ways norm transformation might be occurring in strategic nuclear doctrine. Unlike conventional bombing campaigns, nuclear doctrine has continued to be justified in terms of norms of deterrence and destruction. When nuclear weapons are used to deter -as opposed to being used in pursuit of military victorythen they are ethical. Over the last decade, we have seen significant contestation around the ethics of nuclear weapons. Advocates of the Treaty to Prohibit Nuclear Weapons, for example, reject the argument that nuclear arsenals are moral if they provide an absolute deterrent against major-power war, declaring that nuclear deterrence is 'an outdated military security concept originating from cold war enemy and threat perceptions' . 109 Conventional norms analysis might see the nuclear-ban movement as evidence that the nuclear taboo has strengthened, so much so that nuclear weapons are close to being prohibited as legitimate weapons.
A pragmatic approach shines a light on possible unintended consequences of this process of contentious moral reasoning. The United States' recent nuclear modernisation efforts, especially its investment in low-yield, precision nuclear weapons such as the B-61 gravity bomb, have allowed some to co-opt the nuclear-ban argument that strategic nuclear weapons are inhumane because they are indiscriminate. But instead of arguing for a ban, the purported answer to this moral problem of strategic nuclear doctrine lies in building more precise weapons with significantly smaller blast damage. As one former member of President Bush's National Security Council wrote, 'the moral critique of nuclear weapons seems persuasive when applied against strategic weapons. Strategic weapons make no pretense of discriminating between soldiers and civilians. Their very purpose is to target civilians and the cities they live in and threaten mass annihilation' but that 'tactical nuclear weapons could conceivably be used in an actual military scenario and might pass the tests of discrimination and proportionality' . 110 Likewise, Charles Dunlap notes that if precise, low-yield nuclear weapons are used against military assets, 'nuclear weapons could meet the Just War theory criterion that the weapon not cause more destruction than the harm it is addressing' . 111 As Scott Sagan argues, 'such weapons would make U.S. deterrence both more ethical and more effective -more ethical because they could be used to kill only leaders and military personnel 108 Amos Fox, 'Precision fires hindered by urban jungle' , Association of the United States Army, 16 April 2018, available at: {https://www.ausa.org/articles/precision-fires-hindered-urban-jungle}. 109 Statement of Ambassador Alexander Kmentt (Austria), Second Session of the Preparatory Committee for the 2015 responsible for acts of aggression, and more effective because they would make the possibility of U.S. retaliation inherently more credible' . 112 None of this is to say that advocates of precision nuclear weapons and discrimination will win the day. But it is a process of normative contestation that we have seen before, and the debate might very well be settled in the realm of practical military doctrine.