The scale of Russian aggression against NATO airspace after its initial invasion of Ukraine in 2014 has led the alliance to increase its aerial policing missions, adding efforts in Romania (Mihail Kogalniceanu Air Base) and Bulgaria (Graf Ignatievo Airforce Base). Each of these missions consists of the persistent presence of a squadron minus fighter aircraft (i.e., 4–6 aircraft) and 100–200 support personnel that operate alongside a similar number of host nation platforms.
Doctrinally, these aircraft and their support personnel conduct counterair missions, including area, point, self-defense, and high-value asset protection that operate alongside passive detection ranging from defensive hardening and operational security measures to early-warning and mobility. In short, any aerial policing mission in Ukraine is not limited to aircraft but will need to involve robust planning and integration with existing air defense systems—with the Ukrainians—to deny Russia the ability to use airpower to threaten the peace. A point defense strategy concentrates defensive resources around key locations to protect critical assets. While this approach can impose significant costs on an attacking force, it remains inherently limited since it does not threaten the adversary’s counterair capabilities nor extend control beyond the immediate area of defense. By definition, a point defense involves a smaller number of aircraft since the scope of the defensive counterair mission is reduced to defending critical assets (e.g., an airbase, critical infrastructure, or the political center of gravity).
In contrast, an area defense strategy seeks to deny the enemy the ability to operate across a broader battlespace. This expansive approach tends to mix a larger number of combat air patrols (CAPs) with layered active and passive measures, creating a layered defense-in-depth approach. Active defenses include surface-to-air missile (SAM) launches, fighter intercepts, and electronic warfare emissions used for early warning and engagement. Passive defenses—such as camouflage, decoys, and passive electronic intelligence gathering—enhance survivability by complicating enemy targeting efforts. They also include mobility, as seen in concepts like Agile Combat Employment in the U.S. Air Force.
Surface-to-air systems offer a more efficient means of anchoring both point and area defenses. Unless air forces possess an overwhelming advantage in air superiority fighters, CAPs and ground alert aircraft should be used sparingly—to reinforce high-value targets, concentrate defenses against expected attacks, or cover gaps between SAM systems. The most effective approach integrates both air-to-air and surface-to-air systems, creating a coordinated defensive network that is harder to overwhelm, flank, or bypass than any single-layered defense.
Maintaining a 24-hour CAP requires a minimum of two aircraft per airborne fighter, significantly reducing the number of available aircraft for offensive operations. Furthermore, maintenance rates tend to range between 60–80 percent for combat aircraft, with the average for U.S. aircraft around 70 percent. This means that 24-hour, minimal coverage requires at least 20 aircraft to produce continuous four-hour caps. That number is higher when one considers factors like crew rest and maintaining at least two additional fighters on strip alert to respond to a surge in enemy activity. As a result, the number is more likely 26 fighters, making the required size to conduct an aerial policing mission per region closer to an expeditionary air wing than a squadron.
Current NATO aerial policing missions tend to be much smaller point defenses—essentially aerial tripwires—and involve squadron rotations from NATO members (4–6 aircraft) supported by a few hundred personnel. This structure relies on infrastructure investments in key airbases alongside the larger integration into the intelligence and rotational defense capabilities linked to the NATO Integrated Air and Missile Defence System (NATINAMDS). Returning to counterair and defense-in-depth concepts, these missions can be smaller because they are interoperable and integrated with a larger mix of active and passive ground-based layers.
This contrast provides a point of departure for estimating the number of aircraft required for securing the peace in Ukraine. Assuming that NATO, the European Union, or some other coalition is successfully integrated with Ukrainian air defense and leveraging external intelligence and support assets—including refueling—Ukraine would need a minimum of 24 aircraft operating out of three airbases in country (this would consist of four to six squadrons, based on the Baltic Aerial Policing mission, under which nations send four aircraft squadron minus rotations per mission as a planning factor). If the aircraft operate out of country, that would increase the number significantly, since every hour spent flying to one’s patrol area results in less time to operate. These aircraft—again the minimum—would also have to be sourced on top of existing missions in the Baltics, Romania, and Bulgaria, placing a larger tax on European air forces if the United States is not part of the mission. This is compounded by the fact that it takes two squadrons to deploy one combat squadron forward. This pushes the minimum number of aircraft linked to the mission up to 48 fighters.
For a more expansive area defense, this number would grow to almost 160 aircraft operating in three sectors along Ukraine’s border with Russia and Belarus. This estimate is based on four-ship CAPs with a supporting strip alert per patrol sector. This number would likely require contributions from non-NATO members, which could include support personnel and ground-based air defenses. There would need to be similar commitment of early warning aircraft (AWACS) and refueling aircraft not accounted for above. This effort would also impact the service life of the fighter aircraft in multiple air forces.
Deterrence Takes Flight
Absent a strong air deterrent, Moscow is likely to test the resolve of Kyiv and Western states through air and missile strikes consistent with patterns seen in its firepower strike campaign to date. In an effort to coerce political leaders, these terror attacks involve targeting critical infrastructure and civilians as much as they do legitimate military targets. Supporting Ukraine requires taking this option away from Putin through building a robust aerial policing mission that supports any ceasefire and the associated transition to a peace process, which is likely to last years.
Benjamin Jensen is the director of the Futures Lab at the Center for Strategic and International Studies in Washington, D.C. Mark Montgomery is a retired Navy rear admiral and a senior fellow at the Foundation for Defense of Democracies. Jose M. Macias III is an associate data fellow in the Futures Lab within the International Security Program at CSIS.