With a NATO war and Ukraine's knack for shooting down planes in mind, Russia is holding back its airpower and most advanced jets

• Russia is holding much of its airpower and more advanced jets in reserve, experts say.

• One concern for the Russians is Ukraine's air defenses, which have shot down a number of Russian aircraft.

• Another consideration is that these assets could be needed in a larger potential war with NATO.

Russia has kept much of its airpower and some of its most advanced aircraft out of the war in Ukraine. Experts say doing so signals Russian worries about Ukraine's air defense game but also considerations beyond this fight to one with NATO.

John Baum, an air power expert at the Mitchell Institute and retired US Air Force lieutenant colonel, told Business Insider that the Russians "could bring more advanced aircraft into the fight and they simply haven't done that yet."

Some Kremlin claims aside, there is no evidence Russia has used its Su-57s over Ukraine itself, despite the aircraft, at least on paper, being Russia's most advanced plane and supposedly built for a war in which the airspace is heavily contested.

The jet is Russia's first attempt at a fifth-generation fighter, touted by Russian media as a match for American fifth-generation stealth fighters like the F-22 and F-35. However, given limitations in the design, such as a lack of all-aspect stealth, analysts question whether the plane's actual capabilities fit that description. The aircraft also suffers from some lingering technical issues.

In January, the UK Ministry of Defense said the Su-57 had been limited to launching missiles from Russian territory, mirroring how the Russians have used many of its other aircraft in this war.

Unlike the ground troops it throws into the meat grinder, Russia tends to use its air assets in ways that minimize risk by keeping them back from Ukraine's defenses.

"Russia is husbanding a lot of its air assets. So, a lot of the Russian Air Force, you are not even seeing over Ukraine," Andrew Curtis, an independent defense researcher who spent 35 years as a UK Royal Air Force officer, said. And he said Russia is using Su-57s in ways that there is "no risk."

Curtis said he thinks "the reason for that is simply that it is keen to make sure that it retains a credible modern air force for any future operations that it might want to undertake."

"And that in itself is quite significant," he said, "because it shows that at least somebody in the Kremlin is thinking beyond just Ukraine."

Russia is holding back its air forces with NATO in mind

Michael Clarke, a Russia and Ukraine expert and a UK national security advisor, said Russia is making some sacrifices in Ukraine for a possible future conflict. "If the Russians were throwing everything they had against Ukraine, they would probably be in a stronger, better position than they are now," he said.

He added that Russia's air force is holding back jets "because if it devoted all to Ukraine, it feels it will have nothing left if it comes to some sort of conflict with NATO."

The top US commander in Europe, Gen. Christopher Cavoli, told Congress in April that Russia has only lost about 10 percent of its fleet in Ukraine, indicating it has a lot left in its airpower arsenal.

NATO members are worried about the future threat from Russia, with many warning Russia may attack another member in Europe if it's not defeated in Ukraine.

Members are ramping up defense spending and making more defense agreements with each other, with the ones closest to Russia boosting their border defenses.

Clarke explained that "as this crisis goes on, the prospect of a general war against NATO becomes more real. That's not to say that that's very likely, but it's at least a bit more likely than it was two years ago."

Russia's air force would likely lose in a direct engagement with NATO air forces, multiple experts have told BI, as NATO's combined airpower is much larger and more advanced. But Baum and other air warfare experts have warned Russia's air force should not be underestimated and cautioned that NATO should be ready.

Russia's air force is weaker than NATO's airpower, but Russia's war in Ukraine shows it can still cause a lot of damage. It adapts in devastating ways, as it has demonstrated with the guided glide bomb operations against Ukraine.

Peter Layton, a fellow at the Griffith Asia Institute and a former Royal Australian Air Force officer, said that Russia may very well have a future NATO conflict in mind as it makes decisions today.

For instance, Russia may believe that in a war with NATO, its air forces can "survive long enough to counter some NATO air raids and help defend Russian ground forces for a short time." Such a plan would require not squandering assets in Ukraine. And Layton wasn't the only expert to share in that assessment.

Russian considerations may, in turn, be shaping current combat conditions in the war in Ukraine. "NATO's power in the air is inhibiting the Russians from committing all of their air power, or more of it, to Ukraine," Clarke said.

He said Russia wants to keep its air force looking strong as a weaker Russian air force would "weaken Putin's political hand in anything he then tries to do in relation to NATO politics." And, in a future conflict, Russia would want its air force to be powerful.

Ukraine is still downing Russian jets

The Ukrainian armed forces have a significantly smaller and older air force than Russia does. Its few jets are all Soviet-era, but Russia has one of the world's biggest air forces with many more modern combat aircraft.

But neither side has been particularly successful at changing the war from the air considering the threat posed to aircraft by the proliferation of ground-based air-defense systems.

Air warfare experts previously told BI that Ukraine's achievements here are remarkable and ones that may have stopped the war from quickly ending in a Russian victory.

Russia's losses are much higher than Ukraine's, though it has more to lose. According to an update from open-source intelligence site Oryx in February, Ukraine has lost at least 135 fixed and rotary-wing aircraft while Russia has lost nearly double that figure.

Ukraine has claimed some big kill streaks shooting down Russian aircraft, including downing 10 jets in 10 days in February. Russia's air force often appears to back off after such victories.

Beyond fighter jets and fighter-bombers, Ukrainian forces have also downed some high-value Russian aircraft. This includes an A-50 command and control aircraft in January. The Russians only have a few of these planes available.

This prolific threat to anything flying would potentially put Russia's advanced Su-57s at risk were they to fly combat missions over Ukraine. But avoiding the fight has not completely shielded the small Su-57 fleet. Ukraine managed to damage one in a long-range strike on an air base hundreds of miles inside Russian territory.

Holding its airpower back has largely protected the force, though. Layton said Russia has kept many of aircraft out of Ukrainian airspace since "at least after the first few months." Russia's air force has suffered high attrition rates from Ukraine's ground-based air defenses when operating in the country.

Russian combat aircraft tend to use weapons that let them "generally stay safely inside Russian airspace while firing into Ukraine." Russia notably saw big aircraft losses in February when more of its jets came close to the front lines to support land forces by launching glide bombs, Layton noted.

He said that Russia "has a lot of trouble replacing lost advanced aircraft," only making a few a year. And sanctions from many countries against Russia for its invasion could make things more difficult, he said.

Clarke said that Russia could use its strategic bombers more effectively if they flew over Ukrainian territory, but "they've only got a certain number of strategic bombers, and if they lose eight or 10 of them, then that will put quite a hole in the force."

He said the environment in Ukraine is too "risky" for Russia's air force, especially if it wants to maintain its force for a future fight.

Russia's comfortable losing what it's losing now

Curtis said Russia is using its most advanced assets in ways that keep them "completely safe," like launching long-range attacks from inside Russia. There's "effectively no risk," he said.

And Layton said Russia may be motivated by its own weapons industry, which has ramped up but still faces challenges. "Any losses impact possible future export sales as Russian aircraft now appear less capable," he said. Some experts have suggested this as a possible reason for keeping the Su-57 out of the fight, especially given Russia's significant activity in foreign arms sales.

George Barros, a Russia analyst at the US-based Institute for the Study of War think tank that has been closely tracking the war, said Russia only has a small number of many of its most advanced aircraft, which means they wouldn't make a big difference if Russia was taking on NATO's air forces, though Russia has other capable platforms to supplement.

He said that Russia has a propaganda reason for keeping them intact before any future conflict, one that even outweighs the effect they could have in Ukraine.

On the Su-57, he said, "if the Russians were to lose it, it would be just such an international embarrassment."

Experts previously told Business Insider's Jake Epstein that the absence of the Su-57 suggests Russia may not be confident in the jet and likely wants to avoid any potential reputational damage that would come if any were shot down.

Gustav Gressel, a Russian defense policy expert at the European Council on Foreign Relations, said Russia has "very few" Su-57s, and "they are expensive to operate." Other jets can do the same jobs needed in Ukraine, he said, "and it would be less embarrassing if they would be shot down." Russia is understood to have only around 20 Su-57s in service.

Tim Robinson, a military aviation specialist at the UK's Royal Aeronautical Society, said that Russia's Su-57s "are the high-quality assets, high expensive assets, stealth fighters, and they don't want to lose them."

Experts have also pointed to Russian fears that if its most advanced jets were shot down over Ukraine-held territory, it would expose their most advanced technology and could be a windfall for Ukraine's Western partners.

Robinson said that if any Su-57s are shot down over Ukrainian-held territory, Western intelligence experts would get" to crawl all over it and find out its secret."

Baum said Russia's decisions on what goes into Ukraine and what doesn't may be "calculated." They may have decided "that they don't need to roll out their more sophisticated weapons yet or ramp up their sortie rate yet," he explained.

Curtis said that Russia is "happy to lose what it's using in Ukraine. And in most instances, I'm afraid, that's people." Russia has been known for treating its soldiers as disposable, including by using what are described as "meat grinder" tactics, such as high-cost "human wave" assaults.

He said that for now, Russia can afford to keep its most advanced assets out of Ukraine as its strategy for victory isn't by total military triumph. Instead, he said, Russia aims to grind down Western appetite for helping Ukraine and exhaust Ukraine's support.

He said Russia is "not really going to be too fussed about how modern and how useful the capability" it gives its soldiers is.

Defense reporter Jake Epstein contributed to this reporting.

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