Ukraine's F-16 fighter jets didn't have enough missiles to shoot down Russian drones and missiles for more than three weeks after supplies from Kyiv's partners dried up just as Moscow was preparing a massive winter air campaign, three sources said.
The acute shortage from late November to mid-December, which has not been previously reported, lays bare the vulnerability of Ukraine's air defenses that rely heavily on Western allies for missiles and defense systems to repel frequent Russian strikes.
Kyiv has often complained about a lack of weapons since the war began four years ago, sounding the alarm over critical shortages in recent months while seeking not to anger President Donald Trump's administration.
The need for Western arms is unlikely to diminish soon. With no end to the Ukraine conflict in sight and the war against Iran raging, competition to secure defensive weapons in the Middle East and beyond is likely to intensify.
The three sources, all with direct knowledge of the situation, said Ukraine had only a handful of U.S.-made AIM-9 Sidewinder air-to-air missiles for its entire squadron of F-16s when supplies stopped.
Hundreds of thousands of Ukrainians have survived the worst of a bitter winter without heating, electricity, and running water as a result of an intensifying Russian onslaught on the energy system that Ukraine has been unable to completely repel.
Despite Ukraine's vocal lobbying, concrete examples of how shortages affect its defense capabilities are normally kept secret. In this case, one of the sources told Reuters that Ukraine had nothing to put on its jets for almost a month.
All three sources asked not to be named to describe sensitive battlefield vulnerabilities caused by interruptions to weapons flows.
Reuters could not establish the cause of the shortages, nor whether the delays were down to U.S. or European foot dragging. The first source said Ukraine's foreign partners had told Kyiv they had no available stocks, without specifying which partners.
In response to a request for White House comment, a U.S. official said Washington was committed to stopping the war and supported Ukraine by selling U.S. weapons through NATO. The official said Trump's administration had made "tremendous progress" toward a peace deal between Ukraine and Russia.
The U.S. Department of Defense, Ukraine's air force, and the Ukrainian presidency did not respond to questions.
During the shortage, F-16 pilots flew daytime sorties and tried to hit drones with rotary cannons, a second source said, adding that it was too dangerous to conduct such missions in the dark even though Russian drone attacks usually happen at night.
Pilots also tried using missiles that had failed to fire on earlier missions in the hope they would work after maintenance, the source said. In some cases they were successful.
Ukraine's F-16 pilots have relied heavily on variants of AIM-9 missiles known as Limas and Mikes that were produced in the 1970s and 1980s, the sources said.
Though decades old, those missiles have provided Ukraine with a relatively cheap way to intercept Russian drones and cruise missiles, the three people said.
The shortfall was plugged in December when Ukraine received AIM-9 air-to-air missiles from partners, the three sources said, shortly before a major Russian attack. They declined to name the country or countries behind the delivery, citing secrecy.
Reuters could not determine the impact of the temporary missile shortfall. The first source said it had not coincided with the largest Russian attacks of the winter.
A fourth source, who also declined to be named, said NATO members Germany and Canada had supplied Sidewinder missiles in recent months and confirmed there had been a "bit of a dip" in supplies before, although they declined to say why.
Germany's defense ministry declined to comment on specific deliveries or weapons for security reasons. Germany has been one of Ukraine's biggest military and financial backers since 2022.
Canada's Department of National Defense told Reuters it was in the process of donating AIM-9M-8 missiles from Canadian Armed Forces stocks. "This new donation will complement the past donation of hundreds of Canadian AIM missiles and related components that are being used by Ukraine for its air defense."
Trump introduced a system for supplying U.S. weapons to Ukraine, replacing direct military aid sent under his predecessor, Joe Biden.
Under the PURL (Prioritised Ukraine Requirements List) mechanism, the U.S. sells weapons to NATO allies for delivery to Ukraine.
Asked to comment, a NATO official said PURL was providing crucial U.S. material and, since summer, had supplied about 75% of all missiles for Ukraine's Patriot air defense batteries and 90% of ammunition for other air defense systems.
Nevertheless, Ukraine still faces a challenge to secure enough missiles for its sprawling air defense network.
Russia fires several hundred attack drones and missiles during its large attacks, and Ukraine tries to down them with gunfire from trucks, electronic jamming, interceptor drones, as well as air-to-air and ground-to-air missiles.
President Volodymyr Zelenskyy issued an urgent plea about the shortage of ammunition in January, especially for the U.S.-made Patriot system that Ukraine relies on to shoot down Russia's Iskander ballistic missiles.
F-16s, which were supplied by Kyiv's European partners in 2024, are part of the airborne component of Ukraine's air defense network, along with helicopters and other warplanes.
F-16s have intercepted 2,000 drones and missiles during sorties in an air defense role, the second source said.
Ukraine and its partners have not revealed how many F-16s are fighting in Ukraine. The second source said the number was in "the dozens" but declined to elaborate further.
The F-16s can carry AIM-9s, or more sophisticated AIM-120 missiles. They are produced by Raytheon, a unit of U.S. defense group RTX Corp.
When asked for comment on the shortages, RTX referred Reuters to the U.S. government.
Each AIM-120 missile costs well over one million dollars, two of the three sources said, meaning they are not typically used at scale to counter cheaply produced Russian attack drones.
Those missiles are also used in Ukraine's Norwegian-made NASAMS surface-to-air systems, meaning that during the supply squeeze their operations were curtailed, the last of the three sources said.
That person also said there had been a shortage of U.S.-made RIM-7 missiles which Ukraine has used in modified Soviet-era air defense systems since the 2022 invasion.
The Norwegian defense ministry said the government had delivered a "substantial number" of interceptors for NASAMS earlier this winter ... "so that the NASAMS system can continue to protect Ukrainian citizens from deadly air strikes."
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