Currently more than 50 percent of the world population lives in urban areas, likely to increase to 70 percent by 2050. The future of war is urban, and the American military is coming to terms with that reality, but the current urban operations discourse features a pervasive argument that American military forces “have not exploited contemporary technologies … on the urban battlefield,” including the use of chemical irritants or “tear gas.”

A vocal chorus of critics insist that the effectiveness of American troops fighting in urban areas during future conflicts will be undermined by excessively restrictive rules surrounding employment of tear gas. However, these commentators misinterpret the current U.S. government view of applicable law and policy, potentially eroding legal maneuver space and constraining opportunities to better protect civilians during urban operations.

Myth: Tear Gas is “Banned” During Armed Conflict

Thinkers focused on urban operations, to include during lectures and commentaries for the Army’s urban operations “think tank,” the Modern War Institute’s Urban Warfare Project, lament that “[w]hile tear gas is widely used for crowd-control purposes in urban policing, it is off limits to the US military in combat.” This is not a correct or complete statement of international law or state practice as articulated by U.S. government policy, and it risks depriving a future commander of a tool she could consider employing during urban combat in the limited circumstances explained below. This mistaken view of the legal landscape is widespread, although by no means universal.

International law bans chemical weapons, primarily via the 1925 Geneva Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare (“Geneva Protocol”) and the 1993 Chemical Weapons Convention (CWC). The United States has consistently taken the (minority) position that the Geneva Protocol does not apply to tear gas. The CWC does not treat tear gas as a banned chemical weapon, instead classifying it as a riot control agent (RCA). Article II(7) defines RCA as “[a]ny chemical … which can produce rapidly in humans sensory irritation or disabling physical effects which disappear within a short time … .” CWC Article I(5) prohibits using RCA “as a method of warfare,” but does not define the term method of warfare, leading to a potential exception or “loophole.”

The United States signed and ratified the CWC. Although the United States registered a formal reservation (a way of objecting to portions of a treaty as not being binding international law) that reservation had nothing to do with tear gas and the CWC itself says such reservations are void (Art. XXII states that “[t[he Articles of this Convention shall not be subject to reservations”).

The American View: Defensive Use of Tear Gas is Permissible

The domestic legal regime surrounding the CWC preserves legal maneuver space to employ RCA under some circumstances. The U.S. Senate ratified the CWC in 1997, but with the express requirement that “the President shall certify to Congress that the United States is not restricted by the Convention in its use of riot control agents.” This ratification statement was intended to clarify the existing policy of the United States, laid out in Executive Order 11850, that RCA are prohibited “in war,” but with the exception that RCA may be used “in defensive military modes to save lives” when approved “in advance” by the President. (A good primer on the history of U.S. employment of RCA is available here.)

Thus, whether RCA may be used during war depends on whether RCA are being employed “as method of warfare,” which is prohibited, or “in defensive military modes to save lives,” which can be authorized. Executive Order 11850 does not define “defensive military modes,” but provides a list of examples, including rear-area and prisoner riot control and “situations in which civilians are used to mask or screen attacks and civilian casualties can be reduced or avoided.”

The presence of civilians is one of the salient features of combat in urban environments, and the law of war imposes a requirement to take feasible precautions to protect those civilians (alongside the bedrock distinction and proportionality requirements). An enemy who intentionally fights among non-combatants for the purpose of shielding his forces from attack violates international law and bears responsibility for harm to those civilians, but attacking forces must still take feasible precautions to distinguish between the enemy and human shields.

Despite initial concerns that the CWC prohibited the use of RCA in situations where combatants and noncombatants are intermingled, ultimately the position of the United States as stated in formal guidance updated as recently as 2015 is that use of RCA in defensive modes remains lawful in such situations. Presidential authority to conduct military operations is conveyed through the Secretary of Defense, who typically directs the Chairman of the Joint Chiefs of Staff to publish an Execute Order (EXORD) that provides direction and delegates authorities to military commanders. That EXORD or accompanying Rules of Engagement (ROE) could authorize commanders to employ RCA as a feasible precaution to prevent civilian casualties in an urban attack.

Employment of Tear Gas in Urban Operations

If a U.S. military unit were ordered to conduct operations in a city, the commander could consider employing RCA in defensive military modes during the operations, so long as the governing ROE granted her that authority. The legality of RCA employment would depend on the particular facts and circumstances, to include the commander’s intent. For example, if enemy fighters have fortified a structure by cutting firing ports into the walls, placing sandbags in the windows and doors, and otherwise transforming the building into a defensive strongpoint, and the commander was reasonably certain (a term familiar from contemporary targeting decisions that is the same as the international law term good faith belief) that there were civilians in the structure masking or screening the enemy’s attack positions, the commander could deploy RCA so long as her intent was to separate the civilians from the combatants and protect the lives of the civilians.

A likely effect of deploying the RCA to safeguard the civilians is an increased ability to target enemy combatants when the civilians ‘flush’ from the structure to avoid the effects of the RCA. While this advantage is permissible under the doctrine of double effect, the deployment of RCA as a ‘fig leaf’ to gain a military advantage would be unlawful. The deployment of RCA would also be illegal in situations when the commander was reasonably certain that there were no civilians intermixed with the fighters – such offensive use of RCA is forbidden.

Even Lawful Employment of Tear Gas Carries Risk

The employment of RCA in defensive military modes may be lawful and in accordance with policy, but it is not without risk. In many cases, it could be an example of “lawful, but awful” or “legal, but stupid,” and any commander considering employing RCA should consider the likely implications of that decision.

First, negative media coverage is almost guaranteed, and reliance on a thinly-sliced, heavily-lawyered justification is unlikely to successfully counter the narrative that American forces are gassing civilians in flagrant violation of international law.

Second, many U.S. allies and partners will not agree with the legal analysis, as non-governmental organizations and the manuals of many militaries argue that RCA are totally “prohibited in armed conflict” aside from controlling rioting civilians or prisoners.

Third, the use of RCA risks escalation, to include eroding the consensus against deployment of lethal chemical weapons.

Fourth, ROE that implement RCA use (compared by Donald Rumsfeld as a fighting from inside a straightjacket) are inherently complicated and may be difficult for lower-level commanders and soldiers to apply during a fight.

Finally, there is very little limiting principle aside from a reasonable certainty that civilians are intermixed with fighters and that RCA would help to separate those civilians to prevent them screening or masking enemy attacks – in other words, the authorization to use RCA quickly risks quickly becoming the norm instead of the exception in urban operations. On balance, a commander might well conclude the downside of RCA employment outweighs the advantages, but her conclusion would rest on a clear-eyed assessment of the risks, not a mistaken belief that RCA deployment was per se unlawful in all circumstances.


RCA may not lawfully be deployed to deliberately target combatants, but it is misleading to claim they can never be employed during combat. Whether the next fight is against a near-peer in a megacity or continued stability or counterterrorism operations, commanders should understand the lawful available options to determine how best to fight and win the nation’s wars, in addition to how best to take the feasible precautions that may be available to protect civilians in conflict environments. Mastery of the law and principled counsel are critical ingredients for future success, and national security leaders do well not to be blinded by the fog surrounding the legality of employing tear gas.

(Note: The views expressed do not constitute legal advice and are not a substitute for consultation with an organization’s servicing operational law attorney. The views are those of the author and do not reflect the official position of the United States Department of Defense.)

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