How long can Ukraine hold out in the war for the skies?
On paper, Russia's military prowess implies that along with quick ground victories, the Russian air force should have been able swiftly to take control of the skies. Going into the conflict, Russia's 1,391 aircraft to Ukraine's 132 -- complemented by 948 helicopters to Kyiv's 55 -- have yet to give Putin the kind of aerial dominance required to eliminate Ukraine's resistance. Russia's overall defense budget of $45.8 billion is almost 10 times that of its neighbor.
Experts ranging from former air force personnel to government officials believe that Russia's failure comes down to a combination of poor preparation by Moscow, a clever use of resources based on intelligence by Ukraine and the targeted donations of arms from Western allies to Ukraine.
"As far as I understand, they were able to save a large part of their air force by moving planes from airfields before the Russians destroyed them, based on intelligence ahead of attacks," says Gen. Riho Terras, a former commander of the Estonian Defense Forces.
Sophy Antrobus, research associate at Freeman Air and Space Institute and former officer in the UK's Royal Air Force, agrees that in the early stages of the war, Ukraine appeared to take intelligent steps that are now paying dividends.
"They've been clever in that they didn't deploy all of their resources that could take down Russian aircraft. This possibly led Russia into a false sense of security, and Ukraine has been able to keep defending its air while reinforcements from allies arrive," she says.
Those reinforcements -- S-300 anti-aircraft systems, Stingers and Javelin missiles that have been used by Ukraine so far. The presence of such missile systems marks a dramatic upgrade for Ukraine.
Rep. Mike McCaul, the ranking member on the US House Foreign Affairs Committee told CNN that S-300s, which are Russian-made, have "higher-altitude" capability than Stinger missiles, which the US has also sent to Ukraine.
"The S-300s are the high-altitude -- sort of like our Patriot battery of missiles -- anti-aircraft system. The fact that they are in country and more are coming is going to be very effective." While these missile systems might be effective, there is still a question mark over how long Ukraine can hold off Russia -- both in the air and on the ground.
High risk to Russia
It remains the case that Russia's military is much larger, that NATO is unwilling to get directly involved or set up a no-fly zone and that, the longer the war drags on, the more Ukraine will rely on its allies to provide lethal weapons.
How long it lasts depends in part on how much Putin is willing to throw at winning the conflict -- and whether he wants to repeat the tactics used by Russian forces in support of Syrian President Bashar al-Assad against rebels in his country's civil war, Antrobus says.
"Is he willing to emulate Aleppo and commit atrocities so visible to the rest of the world? The worst days of the war in Syria came years into the conflict, and sadly people were just paying less attention. This conflict is only three weeks old," she says.
If Putin were willing to go to the extremes seen in Syria, Antrobus points out, it would come with a much higher risk to Russia, "because of the anti-aircraft weaponry Ukraine has and is being supplied with."
Russia must consider its medium-long term, she points out: how much in terms of equipment and personnel are they willing to lose at the cost of other interests.
"Placing his own fighters in that level of danger and burning through Russian resources while doing so will be very hard to justify," she says.
What would be a tolerable and sustainable loss to control Ukraine's skies is also an unknown.
Justin Bronk, airpower and technology research fellow at the London-based Royal United Services Institute, doesn't believe that Russia can "attain meaningful air superiority over most of the country without taking unsustainable losses."
"There has been little evidence shown that the Russian air force is capable of the large-scale complex air operations that this task would require."
Russia's battle for Ukraine's skies is in some respects also reliant on what parts of the ground it controls. Terras says that as long "as Russia is still launching most of its attacks from outside of Ukraine, they are limited in how much of Ukraine's enormous airspace they can realistically dominate."
This means that Russia is, in many cases, having to launch bombers from outside Ukraine's borders in order to carry out missile strikes against targets inside Ukraine.
Terras adds that Ukrainian forces have so far been wise in selecting which strategic parts of the country to defend.
No-fly zone plea
The other unknown when it comes to how long this war will last is how long Ukraine's allies can realistically keep providing weapons that the Ukrainian forces are trained to use. Many of the weapons sent, including the S-300s that McCaul told CNN had arrived in Ukraine as of Wednesday, are from the Soviet era and it's unknown how readily they can be resupplied.
NATO has made clear many times that it will not provide a no-fly zone above Ukraine because it doesn't want to get dragged into a NATO-Russia war. The US has discouraged eastern European countries like NATO member Poland from sending weapons for the same reason.
Poland had initially proposed giving all of its MiG-29 fighter jets to US Air Force's Ramstein Air Base in Germany so they could then be provided to Ukraine in its fight against Russia.
However, the US administration quickly called the idea "untenable," because flying the jets from a US and NATO base "into airspace that is contested with Russia over Ukraine raises serious concerns for the entire NATO alliance," according to Pentagon Press Secretary John Kirby.
This is where the optimism of those who have watched Ukraine defend itself hits a major road bump. Even as the US pledges an additional $800 million in security assistance, the West's hesitancy to get directly involved leaves the hardest parts of the job solely up to Ukraine.
"We must deliver more ground-based and air-based defenses that Ukrainians are trained to use. We must consider handing over the Soviet-era planes. There are perfectly good fighter jets sat around Europe that Ukraine is able to use to defend itself," says Terras.
How far the Western alliance is willing to go in supplying this sort of equipment is dependent on politics. The extent to which Ukraine can credibly defend its skies will rely on how far the Western alliance is willing to go. And how long Putin can justify his costly war will be determined by how long Ukraine can credibly defend its skies.
The Ukrainians have done a remarkable job so far in resisting the Russian onslaught. But as the conflict drags on, the fate of the defenders will be left in the hands and patience of others.
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