The Ukrainian Air Force Just Got Bigger. It Seems Someone Gave Kyiv More MiG-29s.

Amazingly considering the odds against them, Ukraine’s airmen have more flyable fighters today than they did in early April, according to U.S. Defense Department spokesman John Kirby.

Kyiv’s air force has “more operable fighter aircraft than they had two weeks ago,” Kirby told reporters Tuesday.

Donations of airplanes, and airplane parts, made it possible. “I would just say, without getting into what other nations are providing, that they have received additional platforms and parts to be able to increase their fleet size,” Kirby said.

It’s not hard to guess what Kirby was referring to. The governments of Bulgaria, Poland and Slovakia weeks ago all signaled some degree of willingness to transfer to Ukraine old MiG-29s or spares for the same.

Despite some diplomatic doublespeak, likely meant to insulate the countries from Russian retaliation, it seems some or all of the three possible donors handed over airframes or parts.

The big question is just what condition Kyiv’s air arm was in as the fresh jets arrived. If the Ukrainian air force continues losing planes at a high rate, the reinforcements might not last long.

The twin-engine, supersonic MiG-29 was the most numerous type in the pre-war air force. As many as 70 MiGs equipped three brigades at three bases with six squadrons between them—one brigade each in the western, central and southern regions of Ukraine.

Su-27 fighters, Su-25 attack jets and Su-24 bombers made up the balance of the Ukrainian warplane inventory, which stood at around 125 flightworthy aircraft when Russia attacked on the night of Feb. 23.

Setting up at small airfields or even roadways—mostly if not entirely west of the Dnieper River—Kyiv’s squadrons survived the initial Russian air raids and rocket barrages. Ukrainian pilots quickly flew into action, tangling with Russian jets and bombing Russian formations on the ground.

Kyiv’s aerial losses were acute in those first few days. Russian air-defenders shot down a pair of Ukrainian Su-25s in the span of a minute near Kherson in southern Ukraine, killing both pilots. A Russian long-range missile battery swatted a Ukrainian Su-27 patrolling over Kyiv, killing the pilot.

In 54 days, the Russians shot down no fewer than 15 Ukrainian jets that analysts visually can confirm. That verified total includes four MiG-29s. Actual losses undoubtedly are higher.

Shoot-downs don’t tell the whole story, of course. Russian forces also have attacked support facilities. On March 18, Russian cruise missiles damaged the State Aircraft Repair Plant in Lviv, in western Ukraine. That facility overhauls MiG-29s.

Moscow is going after Kyvi’s fuel stocks, too. “The Russians are continuously targeting fuel depots of major Ukrainian air bases with their ballistic missiles,” wrote Tom Cooper, an author and expert on the Russian military.

The result was a steady erosion in Ukraine’s flyable fighter fleet. By week four, the Ukrainian squadrons were launching just five to 10 sorties a day, versus the 200 or more sorties the Russian air force was capable of mounting in or around Ukraine. “Every time when I fly, it’s for a real fight,” Andriy, a Ukrainian Su-27 pilot, told The New York Times. “In every fight with Russian jets, there is no equality.”

The tiny Ukrainian bomber fleet, which before the war operated just a dozen or so Su-24s, suffered the most. After a few verifiable missions early in the war and at least three confirmed shoot-downs, the bomber force apparently stopped flying. That is, if the total absence of mentions in any media was any indication.

The MiG squadrons with their greater numbers can endure more losses for longer. It helps that the MiGs mostly fly air-defense missions, many of them over regions where Ukrainian forces remain fully in control. Their pilots don’t necessarily have to fly through Russian air-defenses in order to accomplish their missions.

We don’t know how many MiG-29s Ukraine got from its donor or donors. Maybe Poland transferred all 28 of its old, Soviet-made MiGs, which the country is replacing with new F-35 stealth fighters from the United States. Maybe Bulgaria donated all 15 of its MiGs. Maybe Slovakia sent its 12 MiG-29s. Bulgaria and Slovakia both are replacing their Soviet-made fighters with American-made F-16s.

To be clear, the three secondhand MiG-29 fleets each is slightly different. Unique radio and avionics configurations, for starters. That’s not necessarily a major problem for a desperate air force with an established reputation for adaptation under duress.

In theory, Ukraine could grow its MiG-29 fleet by 55 airframes while also acquiring from its allies spare parts—and possibly fuel—for the MiGs remaining from its pre-war inventory.

The MiG plus-up doesn’t alter the long-term trajectory of the aerial campaign, however. Some or all of those 55 Slovak, Polish and Bulgarian MiG-29s are the only ones readily available to Ukraine. Once they’re gone, further replacements are going to be much harder to come by.

More vexing for the Ukrainians is the pilot problem. Kyiv clearly could source used fighters with just a few weeks of determined diplomacy. But it takes months to retrain formerly inactive pilots—and years to train up new ones.

Ukraine had too few MiG-29 pilots before they started dying in battle with the Russians. The shortfall surely is worse today.

The incredible difficulty of sustaining a boutique manned fighter fleet during wartime helps to explain why drones—both Turkish-made TB-2s and off-the-shelf octocopters—account for an increasing proportion of Ukraine’s air raids on Russian troops.