The United States and its NATO allies are facing forceful calls to impose a “no-fly zone” over Ukrainian skies, with the idea of countering Russian aggression in the region, easing humanitarian suffering, and protecting Ukrainian civilians trying to flee the fighting. Ukraine has requested a no-fly zone repeatedly. In the United States, polling shows this is a popular idea: three-quarters of Americans support a NATO-imposed no-fly zone. But a no-fly zone does not equate to a no-combat zone. Quite the opposite. Enforcing a no-fly zone requires the use of military force, and in Ukraine, that would likely mean confronting the Russian military head-on.

While I sympathize with the no-fly zone’s animating idea—to protect human lives—a NATO no-fly zone simply presents an unacceptable, escalatory risk to the United States and its allies – indeed, perhaps to the whole planet. It opens a Pandora’s box of anticipated and unintended consequences. Even if the no-fly zone is narrowly tailored with the express purpose of protecting humanitarian corridors—as signatories to a recent open letter suggested—it would fundamentally turn on U.S. and NATO military engagement with Russia, a nuclear power with an enormous nuclear arsenal.  Its leaders have already hinted at potentially using them in exactly this context.

Why would a no-fly zone over Ukrainian territory so significantly escalate NATO and U.S. involvement? A “no-fly zone” doesn’t just magically occur by declaring it so. It requires a massive military presence and military enforcement—a point eloquently articulated by Professor Michael Schmitt. Are the United States and NATO willing to use force against Russian assets on the air and ground? Putin has already made clear that no-fly zone participants would immediately be considered part of the armed conflict. And NATO leaders simply declaring to Putin “that they do not seek direct confrontation with Russian forces” would hardly change his view of the incoming aircraft and firepower that would be sent into the combat zone that his forces are directly contesting.

I approach this question from both an operational and a legal perspective.  Twenty years ago, I served as a tactical jet aviator with the U.S. Navy, playing a small role in helping to enforce the no-fly zone over southern Iraq. From personal experience, I can attest that no-fly zones are not benign air patrols. Even in instances where the U.S. enjoys immediate air superiority­ over the skies, we should anticipate that U.S. and NATO planes will be fired upon.  In what follows, I address a host of questions that should be answered and understood well before this is viewed as a remotely credible policy option.

What is a no-fly zone and what would it require in Ukraine? 

At its most basic level, a no-fly zone is an aerial occupation of a designated, three-dimensional geographic space where certain types of flights are prohibited. A no-fly zone is different from the more benign aerial operations that can sometime occur to help enforce economic sanctions or prevent drugs or illegal smuggling.

To enforce a no-fly zone, military air superiority is a prerequisite to protect NATO pilots. This must be established upfront. This will entail destruction of any land-based air defense systems and aerial combat when allied fighters are challenged by Russian fighters. Because of the S-400’s extraordinary range and Russia’s long border with Ukraine, allied fighters would be exposed from surface-to-air threats from both Russia and Ukrainian territory. Failure to destroy the surface-to-air threat exposes U.S. and allied pilots to extraordinary risk. This fundamental point was reinforced by former U.S. Secretary of Defense Robert Gates at a congressional hearing in 2011, when he was asked about a proposed no-fly zone in Libya to protect human lives. He stated:

A no-fly zone begins with an attack on Libya to destroy the air defenses . . .  and then you can fly planes around the country and not worry about our guys being shot down. But that’s the way it starts.

If the United States and its NATO allies are not willing to attack Russian assets upfront, including assets within Russia, their aircraft patrolling the no-fly zone would be heavily exposed to Russian air and ground attacks. Again, this presents a significant and unacceptable risk to American and allied pilots and runs the risk of massive conflict escalation.

Even beyond the need to establish air superiority by attacking Russian assets, enforcing a no-fly zone would require a 24-hour commitment of allied planes.  And this includes not just fighter planes from different participating countries that have surface-to-air acquisition radar with comparable advantages in speed and stealth technology. It encompasses much slower early warning E-3 AWACS aircraft and more vulnerable tanker aircraft to keep the fighters airborne without time-intensive ground refueling.  A no-fly zone would necessitate the establishment of a new, multinational Joint Forces Air Component Command (JFACC) to help coordinate the campaign. This would conceivably be headquartered in a NATO country or on a NATO command vessel such as the USS Mount Whitney.

Would Russia treat this as a new belligerent power and target the JFACC and NATO fighters accordingly? Putin has already said that a no-fly zone is tantamount to NATO entering the war. While Putin’s words can’t be trusted, his full-scale attack on Ukraine demonstrates a shocking brazenness in his willingness to use force.  We simply can’t assume that Putin will back down. Again, a no-fly zone is a significant and extraordinary escalation that could entail a broadening of the conflict beyond Ukraine borders.

Some officials have called on NATO and the United States to implement a “limited” or “humanitarian no-fly zone” to protect fleeing Ukrainians. Don’t be fooled. While I understand and share the noble, human desire to alleviate human suffering, there is not a meaningful difference between a “no-fly zone” and a “humanitarian no-fly zone” in terms of their escalatory risk and implementation. And do we expect that Putin will respect such linguistic nuances? Regardless of a no-fly zone’s label, implementation requires the credible threat of military force where the risk of catastrophic escalation and miscalculation cannot be wished away.

What has been the U.S. experience in recent No-Fly Zones? 

Part of the appeal of the no-fly zone course of action may stem from the somewhat successful implementation of no-fly zones in four military operations in Southern Iraq (Operation Southern Watch), Northern Iraq (Operation Provide Comfort/Northern Watch), Bosnia (Operation Deny Flight), and Libya.

But in all four instances, force was used against allied aircraft enforcing the no-fly zones, and allied aircraft used force in response. These were not benign military operations. All four can be characterized as dynamic, kinetic, and deadly. Critically, three of these four no-fly zones were instituted after hostilities had ended, when the United States and its allies enjoyed clear air superiority over the skies. The one exception—Libya—occurred prior to a much broader NATO escalation against Muammar Qaddafi’s regime.

  • Operation Southern Watch & Northern Watch (1991-2003). These two no-fly zones took place in northern and southern Iraq over a 12-year period.  Here,  the United States and its allies enjoyed air superiority following the cessation of major hostilities in the First Gulf War. Following the expulsion of Iraqi forces from Kuwait in 1991, the Kurdish population in the north and the Shia population in the south revolted against Saddam Hussein’s rule. Saddam responded in a brutal manner, attacking Kurds in the north and Shia in the south with airborne attacks from helicopters.

Soon thereafter, the United Nations established a “security zone” in the north, and the Security Council issued Resolution 688 to “prevent the repression of the Iraqi civilian population in many parts of Iraq.” While no single Security Council resolution expressly authorized these no-fly zones, the United States and its allies pointed to Security Council Resolutions 678, 687, and 688 in the aggregate as a legal basis to implement the no-fly zone and protect the Iraqi civilian population. The southern no-fly zone prevented Iraqi flight operations below the 33rd parallel of southern Iraq. The northern no-fly zone was established in northern Iraq, north of the 36th parallel, in an effort to protect the Kurdish population. These no-fly zones were patrolled by American and British aircraft, and were at times helped by the French and Turkish air forces. Both no-fly zones remained in place for 12 years—until March 2003—when the Second Gulf War commenced. The zones were successful to a degree in preventing Saddam Hussein from using force against his people. But despite U.S. and allied air superiority in Iraq, airplanes charged with enforcing the no-fly zone were repeatedly fired upon by Iraqi surface-to-air missiles. Professor Schmitt, a onetime legal advisor on the no-fly zone effort, wrote in the Yale Journal of International Law that  “force was employed repeatedly.”  I share his recollection.

  • Bosnia-Herzegovina (1992,1995): As part of an effort to facilitate humanitarian assistance during the war in Bosnia, the U.N. Security Council adopted Resolution 781, which prohibited all military flights in the area. Following repeated Serb violations of the no-fly zone, the Security Council in March 1993 issued Resolution 816 which authorized member States “acting nationally or through regional organizations . . . to take all necessary measures to enforce the ban.” In response, NATO launched Operation Deny Flight, which lasted through 1995. This mission also involved U.S. fighter jets on patrol shooting down aircraft violating the zone. 
  • Libya (2011). This is the most recent no-fly zone and was put in place to protect Libyan civilians from Qaddafi’s military-backed forces. It was specifically requested by the head of the Libyan National Transitional Council, who were fighting Qaddafi for control over Libya. The U.N. Security Council adopted Resolution 1973, which provided broad legal authorization to impose an international no-fly zone. It is a particularly strong no-fly zone in both its geographic coverage and its legal enforcement authorization.

What are some lessons learned from these recent no-fly zones?

First, in each no-fly zone, the U.S. and allied fighters had air superiority or were able to achieve air superiority in short order. That is not the case in Ukraine, where NATO is left with a terrible choice at the outset. To establish an effective no-fly zone, it must either achieve air superiority upfront by attacking Russian air defenses or place allied aircraft into an area to enforce a no-fly zone without air superiority. This would expose NATO aircraft to deadly Russian fire. The Russians, for example, have a S-400 mobile weapons system with a range of 400 kilometers that could operate in Ukraine or within Russian territory to strike NATO and Ukrainian aircraft.

Second, despite controlling the skies over Iraq, Libya, and Bosnia, U.S. and allied planes were still fired upon and engaged with hostile forces throughout their enforcement missions. For example, an American and a French fighter were shot down in Deny Flight, and Iraq repeatedly fired at aircraft patrolling the no-fly zones through 2003.  We should expect the same to occur over Ukrainian skies, but much more intensely and likely with much deadlier effects. After all, Russian air-to-ground capabilities and its Air Force far outpace Iraqi, Libyan, and Serbian capabilities.

Third, these previous no-fly zones showcased the difficulty of operating in a dynamic airspace where “friendly fire” incidents can occur. This is particularly the case if there is a malfunction in a transponder or other equipment that helps identify friend or foe.  Tragically, in 1994, the U.S. Air Force shot down two U.S. Army Blackhawks in the northern Iraqi no-fly zone. From an operational perspective, Russian air capability outpaces Ukraine’s. Would the introduction of new aircraft for a no-fly zone make it more difficult for Ukrainian fighters on the ground to identify friendly or enemy aircraft?

A snapshot of the recent U.S. no-fly zone experience:

Operation Year Legal Basis U.S./Allied Air Superiority? Kinetic Action?
Iraq – Southern Watch 1991-2003 Security Council Resolutions 678, 687, 688* Yes Yes
Iraq – Northern Watch 1991-2003 Security Council Resolution 678, 687, 688* Yes Yes
Bosnia-Herzegovina – Deny Flight 1992, 1995 Security Council Resolution 781, 816 Yes Yes
Libya- Odyssey Dawn 2011 Security Council Resolution 1973 Yes Yes
Proposed in Ukraine (TBD) 2022 Ukraine permission/Collective self-defense? No ?
* There remains some disagreement about whether these resolutions authorized a no-fly zone.


What laws apply to no-fly zones and what are the rules of engagement?

Ukraine and Russia are engaged in a traditional, international armed conflict. It is certainly lawful for Ukraine to request that other countries come to its aid in collective self-defense against Russia’s aggression. So what would be the status of the no-fly zone participants? As noted, Putin has already made clear that he would consider such an operation as equivalent to NATO entering the war – and in reality, that would be the effect.

Under their rules of engagement (ROE), the U.S. military and allied partners use deadly force in response to a hostile act or demonstrated hostile intent. So many difficult questions flow from just the prospect of placing NATO aircraft in Ukraine’s skies. What if a ground-based Russian S-400 locks onto a U.S. fighter over Ukrainian skies with its fire control radar? This would appear to meet the threshold of hostile intent, justifying a response. Would the United States withdraw or disengage from its mission? Doing so would defeat the purpose of the no-fly zone. Or would it be authorized to fire upon the Russian launcher? Consider, too, that the S-400 could be placed in either Russian or Ukrainian territory—would that matter in the NATO ROE calculus?

Further, what is the outer scope of the mission, and would this include collective self-defense of Ukrainian civilians and military assets, regardless of the threat? For example, would NATO aircraft be authorized to use immediate force – against Russian land or air forces – in defense of Ukrainian civilians who were under attack? What if this threat was occurring outside the no-fly zone?  These are just a few of the questions that should be posed, discussed, and debated before any serious discussion continues on a no-fly zone for Ukraine.

What are the conditions for ending a no-fly zone? 

While this question may seem premature, the U.S. experience with recent no-fly zones and military operations more generally showcases that the United States usually does not put enough thought into exiting before it enters a military operation. Once no-fly zones are imposed, they are extraordinarily difficult to end. Three of the four no-fly zones discussed above only ended with the commencement of major combat operations. The no-fly zones in southern and northern Iraq lasted 12 years, keeping a constant U.S. presence in the Middle East. For the U.S. Navy, this required a permanent aircraft carrier presence in the Persian Gulf.  The U.S. experience with previous no-fly zones as well as our experience in Iraq and Afghanistan highlight the need to think through the exit strategy before even considering the entry strategy.

To be clear, I am horrified at Putin’s actions and what he is doing to the Ukrainian people. And I appreciate the instinct to do something in the face of such horrors. The international community must stand up to Putin, something that it failed to do after his purported Crimean annexation. But the world must stand up to him in ways that do not  unduly risk widening the war. A no-fly zone represents an unacceptable risk to the U.S. and NATO of further, massive escalation and miscalculation.  This could lead to the unthinkable:  direct, prolonged military engagement between Russia and the United States—two major nuclear powers.

The international response to date has been encouraging. The United States and its allies and partners should allow some time for the punishing economic sanctions to take effect while supplying the brave Ukrainians with the weapons and resources they need to continue their heroic fight. But unless conditions in Ukraine fundamentally change, U.S. and allied policymakers should remove any discussion of a Ukraine no-fly zone from the table as a credible policy option.

IMAGE: Members and supporters of the Ukrainian community attend a protest against the Russian invasion and call for a no-fly zone, in Times Square, New York, on March 5, 2022. (Photo by ED JONES/AFP via Getty Images)