Guest Post: “The Chinese balloon shoot-down incident and the law: some observations”

Today’s guest post digs into the legal issues surrounding yesterday’s shoot-down over U.S. territorial waters of a Chinese high altitude balloon (HAB). Secretary of Defense Lloyd Austin says this HAB was “being used by the [People’s Republic of China] in an attempt to surveil strategic sites in the continental United States.” 

In announcing the postponement of his planned diplomatic visit to China, Secretary of State Antony Blinken said “the presence of this surveillance balloon in U.S. airspace is a clear violation of U.S. sovereignty and international law, that it’s an irresponsible act, and that the [People’s Republic of China’s] decision to take this action on the eve of my planned visit is detrimental to the substantive discussions that we were prepared to have.”

Our three guest authors, Lt Col Jay Jackson, Major Aaron Johnson, and Major Matt Montazzoli, are military lawyers but are writing in their personal, not official, capacities.  They expertly unpack several of the legal issues associated with the incident (which are more complex than many might think!) and conclude that “the presence of the HAB in U.S. national airspace was unlawful.” 

Though the illegality would seem obvious to most people, it is actually more complicated.  Why?  Chinese authorities claimed the balloon was of a “civilian nature [and] used for scientific research such as meteorology.” 

Furthermore, China insists it was helpless to prevent the overflight because “[a]ffected by the westerly wind and with limited self-control ability, the airship seriously deviated from the scheduled route.”  It added that China regrets that the airship strayed into the United States due to force majeure.  China contends:

“This is entirely an unexpected situation caused by force majeure and the facts are very clear. China always acts in strict accordance with international law and respects the sovereignty and territorial integrity of all countries. We have no intention to violate and has never violated the territory or airspace of any sovereign country.” (Emphasis added).

The reference to “force majeure” is telling––and clever––because if accurate, it might present a legal defense. Under international law, force majeure is an event that is “unforeseeable, uncontrollable, and makes the performance of an obligation impossible.” 

For example, an unexpected storm may force an airliner to make an unplanned landing in a country without the permission of the nation’s authorities. Such a circumstance could excuse adherence to what would otherwise be the legally-required process to enter a country’s sovereign airspace. 

Such instances of force majeure might excuse a sovereignty violation not just by civilian aircraft, but also by State aircraft, to even include non-hostile military planes.  In a 2001 article two scholars said:

The overflight of sovereign territory by a state aircraft can be justified by reasons of distress or force majeure as an exception to the principle [that state aircraft cannot “fly over the territory of another State…without authorization” as indicated] in Article 3 of the Chicago Convention. Elementary considerations of humanity not only prevent the use of force in such situations, but also override claims of violation of sovereign airspace.

To me, whatever “considerations of humanity” that may support the concept with respect to manned aircraft, they markedly diminish in the context of an unmanned airship drifting for days out of control (if China is to be believed) over sovereign U.S. territory containing sensitive military facilities and populated by millions of Americans.

Fortunately, today’s guest post expertly unpacks the Chinese claim of force majeure and explains why it does not excuse the sovereignty violation in this instance. 

In addressing the idea of self-defense in international law, the authors—based on the current publicly available facts––are doubtful of its application to the shoot-down.  While Article 2 (4) of the UN Charter generally bars the threat or use of force, Article 51 provides that “[n]othing in the present charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs.” 

Many countries take the position that although any threat or use of force is unlawful, forceful acts in self-defense are authorized only when the victim country suffers force of sufficient scope and intensity to amount to an “armed attack.”

As the authors note, the U.S. takes a rather different position.  They explain that “the United States views Article 51 as incorporating, as opposed to displacing, common law self-defense, leaving states free to ‘effectively to protect itself and its citizens from every illegal use of force aimed at the State’.”

They are absolutely correct. In 2012, the then legal adviser to the U.S. State Department Harold Koh said “the United States has for a long time taken the position that the inherent right of self-defense potentially applies against any illegal use of force.”

That said, our writers rightly point out that 1) the Pentagon said the “balloon did not pose a military or physical threat”; 2) that international law generally does not prohibit espionage, and 3) that scholars have “persuasively argued” that, in any event, submarines collecting intelligence in territorial waters does not even amount to a use of force.

Consequently, the authors conclude that the “deployment of an espionage balloon over sensitive military sites probably does not reach the threshold of a use of force” (though they concede that the Pentagon may have information to which they are not privy that could change the analysis).

While that conclusion is an eminently plausible one, and likely to draw agreement from many international law experts, I suggest that where the unauthorized penetration of sovereign airspace is by a physical object the size of this HAB (with a payload that cannot be definitively verified), and that the intrusion persists for days over, as noted above, areas holding sensitive military sites and populated by millions, such circumstances might be enough to constitute a use of force (particularly if the HAB was intended to collect intelligence on “strategic” locations).

Consider this: In the 1986 Nicaragua case, the International Court of Justice found that “by directing or authorizing overflights of Nicaraguan territory [the U.S. had breached] its obligation under customary international law not to violate the sovereignty of another State.”

Obviously, we do not yet know the extent to which China may (or may not) be responsible for “directing or authorizing” the HAB’s flight path (to include reasonably accounting in such “directing or authorizing” for the likelihood of equipment failures and/or inclement weather conditions).  We also don’t know what surveillance equipment, if any, might have been onboard.

Such facts do matter in a ‘use of force’ determination.  Until we know more I am not personally ready to discard the possibility that the HAB overflight could legally constitute a use of force.

Moreover, the fact that a use of force may not be manifested in actual harm at the exact moment the victim State takes defensive action is not, in my view, dispositive as to the legality of self-defense.  For example, the U.S. embraces the concept of anticipatory self-defense in circumstances where no use of force has yet occurred.

To be clear, I am not saying that the shoot-down was a matter of anticipatory self-defense; rather, I am merely using the concept as an example where lawful self-defense does not necessarily require the threat to actually be realized, as the lawfulness of self-defense is not strictly a temporal calculation.   

I can also imagine other circumstances where a proportional use of defensive force to address a foreign intruder (person or object) is justified even though the intruder is not able to mount an effective threat at that moment. 

Such a use of force may be fairly minimal.  In this case, it was a single missile launched under circumstances where no people were at risk, yet it ensured that the HAB—which China claims it could not control—could not again fly over the U.S. landmass and try to “surveil strategic sites.” 

Our writers also reference a post I wrote 2018 about the attacks on Syrian chemical weapons capability suggesting that a new norm could be emerging justifying such a use of force where a jus cogens norm was repeatedly being violated.  Jus cogens refers to certain fundamental, overriding principles of international law, from which no derogation is ever permitted.”  Whether that 2018 argument applies here is something I would need to think about more, but I appreciate the writers raising the idea.

What our guest writers do propose is that “in the absence of other legal authority, the shoot-down could be characterized as a reprisal.”  To me this is a novel—and fascinating—contention, and one worthy of study, so be sure to check out their argument!

Finally, we should be open to examining another justification (and perhaps one worthy of research beyond the scope of this post), because the shoot-down occurred entirely within U.S. airspace and involved an airship known to have entered that airspace without permission. 

In my view, the U.S.–and every country–has the right to defend itself against possible espionage taking place within its borders or in its territorial airspace, and this may principally be a matter of domestic, not international law.

Keep in mind that as a general proposition, international law makes it clear that “each State has complete and exclusive sovereignty over the airspace above its territory.”  Consequently, nations have a right to border security both on the ground or in its airspace, to include the right to inspect and search objects entering or leaving its jurisdiction—which is governed by their domestic law.

For example, in the U.S., border searches can typically be conducted without a warrant or probable cause or even  suspicion about criminality, espionage or otherwise. 

Border security can also include the use of force in a law enforcement context. If, for example, three buses (the reported size of the Chinese HAB) sped through a border checkpoint, U.S authorities would have the right to pursue such vehicles and, as a last resort, use force to stop them.

Also consider the recent incident at Luke Air Force Base.  Though not at a border, the episode does illustrate the importance of security of military locations, and that force––to include lethal force—can lawfully be used to preserve it.  In that case, media reports say “a man drove through the South Gate security checkpoint failing to follow proper protocols.”

Security “teams deployed an automated vehicle barrier” and the man was killed when his car hit it.  These barriers are also designed to prevent, when necessary, vehicles exiting military installations.

Is there something of an analogy here?  Can we not also say that the deployment of a fighter aircraft to shoot down the HAB constituted something of an ‘aerial’ barrier?  Employed as a last resort against an aerial vehicle that failed “to follow proper protocols”?  An aerial vehicle that may have been engaged in unlawful surveillance of “strategic sites”?  One that may take evidence of a crime as it exits (flees?) U.S. jurisdiction?

Along those lines, the U.S. is adamant that the HAB was in its territorial air space and was attempting to “surveil strategic sites” while there.  True, the U.S. has not yet explicitly charged China with attempted espionage, per se, but the specter of it is raised by the allegation.

While international law may not prohibit espionage per se, U.S. law certainly does, so it seems incontestable that the U.S. has the right to investigate such cases when reasonably raised by the facts—and this understandably means pursing evidence that is still wholly within its borders, to include its territorial airspace.  

Dealing with potential national security perils related to an enormous military challenge such as China have to be the government’s priority.  We can’t forget that the Supreme Court says that it is “’obvious and unarguable’ that no governmental interest is more compelling than the security of the Nation.” 

Investigating and halting criminal activity may sometimes require the stopping of a fleeing ‘vehicle’ in any medium.  That process may inevitably require the destruction of property, and doing so may be necessary to obtain and preserve critical evidence that property may contain.  That the U.S. was able to do so in this case without the loss of any life is both remarkable and highly-commendable. 

In sum, though my approach may be a bit different, I agree with our writers’ ultimate conclusion that the shoot-down was lawful.  I strongly invite you to see the really interesting and thoughtful way they came to their conclusion and how they justify it.

(FYI, my intro has been updated and clarified as of 0655 hrs 6 February.)

The Chinese balloon shoot-down incident and the law: some observations

by Lt Col Jay Jackson, Major Aaron Johnson, and Major Matt Montazzoli

This past week, the United States announced that a Chinese high altitude balloon (HAB) was transiting across the United States. The Pentagon assessed with “very high confidence” that the HAB was a Chinese surveillance balloon with a large, apparently technical payload visibly suspended beneath it.

After several days of flying over sensitive defense sites—including one of the U.S.’s three nuclear intercontinental ballistic missile fields – the U.S. Air Force reportedly destroyed the balloon over U.S. territorial waters off the coast of South Carolina.  

The incident caused public uproar, to include passionate demands to shoot down the HAB, some less credible than others For their part, the Chinese claim (somewhat incredibly) that the HAB was simply a civilian weather research balloon that has been blown off course.  Lurking in the ashes of the remains of the Red Balloon Scare are numerous legal issues.

We conclude the presence of the HAB in U.S. national airspace was unlawful. We conclude the U.S. had a domestic legal basis for the use of force against the HAB, and that the attack was justified as a reprisal under international law. 

Historical Precedent

The military use of hot air balloons is longstanding. Leonardo Da Vinci foreshadowed military flying machines, and Ben Franklin imagined a battalion of balloonists. During the American Civil War both sides of the conflict employed tethered balloons for observation and artillery adjustment, including one Union balloon that featured a massive portrait of General George McClellan as a taunt towards rebel forces, and a Confederate balloon manufactured entirely from discarded women’s dresses.

During World War I, the German military used zeppelins to conduct (largely unsuccessful) bombing raids against English cities. During World War 2, Japan released thousands of balloons loaded with incendiary devices, with some sparking forest fires across the western United States and one killing six Americans in Oregon.

During the Cold War, the Soviet Union sharply protested the United States’ practice of sending balloons with “apparatus suspended … include[ing] automatic photographic cameras for aerial photography, radio transmitters, radio receivers and other things.”

The U.S. reply admitted the balloons were “in effect little satellites” and averred they were intended only for meteorological purposes, but agreed to stop flying them over Soviet territory out of a desire “to avoid misunderstandings,” if not out of any sense of legal obligation. Declassified documents later revealed the balloons were, as the Soviets suspected, utilized to gather intelligence.

In recent years, the United States revived the concept of martial ballooning, deploying tethered Persistent Threat Detection System balloons widely at bases across Iraq and Afghanistan (and sometimes accidentally elsewhere). Similar aerostat balloons equipped with cameras and radar make up part of the United States’ border monitoring system. 

The United States military also employs free-floating balloons, reportedly including plans to use them for logistics and as ‘sensor to shooter’ linkages. The U.S. Army has employed  HABs in Europe and the Indo-Pacific, and its allies are doing the same.

Future plans suggest HABs could be used to deploy munitions or drone swarms. However, the United States and other countries have recognized that, unless an effective system is developed to steer them or the munitions have independent guidance, the use of balloons to deliver munitions is inherently indiscriminate and thus unlawful under treaty and Customary International Law .  

What Law Applies?

The navigational regime for the skies within Earth’s airspace differs from the rules for objects in outer space. The governing law for the skies is the 1944 Convention on Civil Aviation, commonly known as the Chicago Convention, which grants states sovereignty in the ‘national airspace’ above their territory, including territorial waters. Objects in outer space are governed by the 1966 Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, intuitively referred to as the Outer Space Treaty (OST).

Neither treaty articulates where national airspace ends and outer space begins, and the United States Department of Defense takes the position that an exact demarcation is unnecessary. China has not formally announced a position on where outer space begins, but co-sponsored the moribund (and given their behavior, cynical) Treaty on the Prevention of the Placement of Weapons in Outer Space, the Threat or Use of Force against Outer Space Objects which defines outer space as 100km above sea level. 

While the law on where exactly earth’s airspace ends and outer space begins is unsettled, both China and the United States consider the elevation at which the HAB operated – reportedly around 60,000 feet – to be well within earth’s airspace, making the Chicago Convention the governing legal regime.

Was the Chinese Balloon’s Presence Lawful?

As a threshold matter, a HAB meets the Chicago Convention’s Annex 7 definition of an “aircraft”  as “any machine that can derive support in the atmosphere from the reactions of the air other than the reactions of the air against the earth’s surface.” This definition encompasses objects that are lighter or heavier than air, to include powered and unpowered balloons, and includes manned and unmanned aircraft.

The Convention divides aircraft into state aircraft and civil aircraft. State aircraft are those “used in military, customs, and police services,” and Article 3 of the Convention prohibits state aircraft from flying over the territory of another state without permission.

Even before China admitted ownership of the balloon, claiming it was a civil aircraft, the United States expressed “very high confidence” the balloon belonged to China, but did not explicitly categorize it as military. Even if the balloon were a civil aircraft, it clearly entered U.S. airspace without a registered flight path, without establishing or maintaining the required radio communication, and apparently without the benefit of an airman in control of the aircraft. Its presence in U.S. airspace was still unlawful.

The Chicago Convention codifies the customary international law norm that states exercise sovereignty over their national airspace, defined as the airspace over their land territory and territorial waters. Unlike the laws governing the sea, there is no right of innocent passage through national airspace – meaning all aircraft must exhibit “due regard” by complying with established procedures to enter another nation’s airspace.

Unmanned balloons in particular may not be operated over a state’s territory without appropriate authorization. (Art 2.2 of Appendix 4). While there is some leeway for small weather balloons the dimensions of the Chinese HAB placed it firmly in the category of an aircraft.

Consistent with the Chicago Convention, the United States maintains a National Airspace System to control the flow of aircraft. Although the Federal Aviation Administration does not typically provide air traffic control for aircraft above 60,000 feet, uncontrolled airspace does not cease to be national airspace.

By statute the federal government maintains exclusive sovereignty over U.S. airspace, and foreign vessels require permission to navigate. There is no indication the Chinese balloon made any attempt to comply with U.S. diplomatic clearance requirements, and a senior U.S. Department of State official left little ambiguity, asserting “the presence of this balloon in our airspace is a clear violation of our sovereignty, as well as international law.” 

Force Majeure

The initial Chinese statement about the balloon asserting that it only entered U.S. territory due to an “unexpected situation caused by force majeure” could be legally significant because aircraft in distress are entitled to entry and emergency landing rights under both Article 25 of the Convention and customary law.

For example, a U.S. surveillance aircraft famously made an emergency landing on Hainan Island in Chinese territory after an unprofessional intercept by Chinese aircraft in international airspace resulted in a collision.

However, one of the key differences between the damaged U.S. aircraft’s landing on Hainan Island and the Chinese HAB is that the U.S. aircraft was a state vessel, entitled to sovereign immunity from search, inspection, boarding and seizure of the craft or crew (not that China saw fit to respect those protections). China’s claim that the balloon was a civil aircraft means it does not enjoy sovereign immunity.

Thus, under the Chicago Convention its privileges to enter due to force majeure are “subject to the control” of the airspace owner. The fact that the PRC only announced the balloon’s alleged distress once the United States had publicly disclosed its unlawful presence in American airspace, along with reports this is part of a pattern and practice of airspace intrusions, argues against any actual emergency, and forensic analysis of the debris will likely prove suspicions of illicit activity were well-founded.

What domestic legal remedy was available?

The United States and allies maintain an Air Defense Identification Zone (ADIZ) around the Canadian and United States national airspace the balloon is alleged to have breached. However, an ADIZ is a regulatory restriction and not a legal one. As the ADIZ is essentially an administrative measure, a violation would not confer any international legal authority beyond that already available for a violation of national airspace, such as the right to intercept, escort, and interrogate to determine hostile intent.

President Biden’s power as commander-in-chief of the armed forces, derived from Article II, Section 2 of the U.S. Constitution, likely provides the domestic legal authority to order a shoot-down (and grim precedent for such an action exists).

In this case the inherent executive authority is bolstered by Congressional assent, in the form of a statute that confers upon the Secretary of Defense authority to designate facilities and assets which may be defended with “reasonable force to disable, damage, or destroy the [threatening] unmanned aircraft system or unmanned aircraft,”  as well as to seize or confiscate the aircraft. 

Among the facilities that the Secretary can designate for protection are those “directly relate[d] to … nuclear deterrence.”  Given public reporting of the HAB loitering over nuclear missile fields in Montana, the statute provides robust domestic authority to destroy and confiscate the balloon, even when the destruction occurred later in time in order to mitigate the impact of falling debris above civilians and civilian objects. 

What international legal remedy is available?

The international legal basis for the shoot-down remains less clear. The Chicago Convention forbids the misuse of civil aviation in Article 4 and recognizes that “every State, in the exercise of its sovereignty, is entitled to require the landing at some designated airport of a civil aircraft flying above its territory without authority or if there are reasonable grounds to conclude that it is being used for any purpose inconsistent with the aims of this Convention,” and authorizes enforcing states to “resort to any appropriate means consistent with relevant rules of international law.”

Two possible international law justifications for the use of force against the HAB are the inherent right of self-defense or reprisal. Here, China’s insistence the vessel is civilian works against it, making it indisputably lawful for U.S. officials to issue orders for the HAB to land and use ‘appropriate means’ to compel compliance.


In general, States must refrain from the use of force in their relations with other states. In the case of an armed attack, Article 51 of the United Nations Charter recognizes that a nation is authorized to respond in self-defense. On its face, a balloon (even were it a state vessel) crossing into territorial airspace is not an armed attack, and therefore probably does not authorize the exercise of national self-defense.

The Pentagon’s admission that the HAB was “traveling at an altitude well above commercial air traffic and [did] not present a military or physical threat to people on the ground” is relevant to actions the United States could take in response, despite the unlawfulness of the aircraft’s presence in U.S. airspace.

Even the announcement of the HAB’s destruction made it clear the U.S. Government believed “[t]he balloon did not pose a military or physical threat.” While it is possible the HAB poses an espionage or cyberspace threat the United States knows about but has elected not to disclose, the repeated characterizations of the HAB as posing no threat make the public case for self-defense unavailing.

Scholars have considered the analogous situation of submarines conducting espionage in territorial waters and have persuasively argued that collecting intelligence is “not an armed attack or even the use of force in international law.”

That said, the United States views Article 51 as incorporating, as opposed to displacing, common law self-defense, leaving states free to “effectively to protect itself and its citizens from every illegal use of force aimed at the State.” DoD LoWM 1.11.5.

The deployment of an espionage balloon over sensitive military sites probably does not reach the threshold of a use of force, but it is possible Executive Branch attorneys with access to all of the facts and circumstances could reasonably counsel otherwise, and in the event the strike is justified under self-defense we can expect the Administration to file a so-called Article 51 letter with the Security Council.


In the absence of other legal authority, the shoot-down could be characterized as a reprisal. The DoD in LowM 18.18.1 defines reprisals as acts by a state that would otherwise be unlawful, but are justified when undertaken to compel another state to cease violation of international law.

Reprisals must be justified; authorized at the national level; may only be undertaken when other methods for securing compliance have been exhausted or are unavailable; must be proportional to the violation; and must be publicly acknowledged or announced as a reprisal.

Given the facts available, reprisal could provide a basis for the shoot-down, although announcements to date have not made this explicit, and DoD’s policy is that “to fulfill their purpose of dissuading the adversary from further illegal conduct, reprisals must be made public and announced as such.”

While statements to this point have noted that the balloon’s “intrusion into American airspace over several days was an unacceptable violation of U.S. sovereignty,” they have yet to explicitly characterize the shoot-down as a reprisal. In the event this was the international legal basis, we would expect the Administration to make an unambiguous announcement.

A Third Possibility?

It is also possible that, as Lawfire’s Charles Dunlap has previously opined “we may be at something of an inflection point where, fueled by state practice like we’ve just witnessed, a norm could be evolving to permit a limited use of force in an effort to stop repeated violations of a jus cogens standard” like sovereignty and control over national airspace.

There is likely a lot of information not publicly available. Strange facts indeed make strange law, and it is always possible the Administration may advance a novel justification for the use of force.


Accepting the United States’ conclusion that the Chinese HAB’s sudden appearance over U.S. territory was by no means accidental, there is little doubt that the incursion violated international law.  Nonetheless–even where the domestic legal authority for destroying and seizing the balloon is clear–the international legal basis for the HAB’s destruction and seizure is perhaps murkier than expected.

Ultimately, we believe the concept of reprisal provides the firmest foundation for the destruction of the balloon. The flagrancy of China’s violation of U.S. territorial integrity and their dilatory and dissembling response provides sufficient justification for Saturday’s shootdown, but to remain consistent with U.S. policy the Administration should announce that the shoot-down was a reprisal as a matter of law.  

Even if that leaves China feeling a little deflated.

About the Authors

Lt Col Jay Jackson serves as Individual Mobilization Augmentee to the Staff Judge Advocate at United States Strategic Command, Offutt Air Force Base, Nebraska. Lt Col Jackson received a direct commission as a judge advocate in September 2006 and served on active duty until June 2020, when he transferred to the Air Force Reserve. He spent his last three years of active duty as Deputy Staff Judge Advocate at Joint Special Operations Command, deploying five times as the senior legal advisor of a special operations joint task force.

Major Aaron Johnson is a U.S. Army Judge Advocate and former Army interrogator and intelligence officer. His current assignment is to the U.S. Naval War College faculty, where he is the Director of Land Operations at the Stockton Center for International Law. He received his LLM from The Judge Advocate Generals’ Legal Center and School, his JD from the J. Reuben Clark Law School at Brigham Young University, and BA in Middle East Studies from the University of Utah. 

Major Matt Montazzoli is an active duty U.S. Army Judge Advocate, currently assigned as Operations Law Officer (Military Personnel Exchange Program) for Headquarters, 1st Division, Australian Army. He received a Masters of Operational Studies from the U.S. Army Command and General Staff College; a LL.M from the Judge Advocate General’s Legal Center and School; a J.D. from the University of Colorado School of Law; and a B.A. from Marymount University.


* The views and opinions expressed here are those of the authors in their personal capacities and do not necessarily reflect the official policy or position of the U.S. Army or U.S. Air Force, the Judge Advocate General’s Corps, the Department of Defense, or any other agency of the U.S. or Australian governments.

The views expressed by guest authors also do not necessarily reflect the views of the Center on Law, Ethics and National Security, or Duke University. See also here.

Remember what we like to say on Lawfire®: gather the facts, examine the law, evaluate the arguments – and then decide for yourself!

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