CNN  — 

It’s the big question that has Russian military commanders scratching their heads: What’s made Ukraine’s air defenses so impenetrable all of a sudden?

This month alone, Russia has launched eight waves of missile attacks on the Ukrainian capital, the latest of them a bombardment in the early hours of Tuesday that involved at least 18 missiles of various types and a swarm of drones.

Yet Kyiv claims to have escaped with barely a scratch, denying any of the missiles or drones hit their targets.

That may be an overstatement – US officials believe a US-made Patriot defense system was likely damaged – but even allowing for hyperbole, experts say it’s clear something remarkable is going on.

Until recently most analysts and even US defense officials simply doubted Ukraine’s air defenses would be up to the job of repelling a sustained Russian assault.

Just last month, leaked US government documents detailed how Ukrainian stocks of Soviet-era medium-range air defense missiles were severely depleted, while even Alexander Rodnyansky, an economic adviser to Ukrainian President Volodymyr Zelenksy, has recently admitted to CNN that his country’s air defenses were “not coping well enough.”

Those assessments followed a March 9 onslaught in which Russia launched 84 missiles at major cities across Ukraine. On that occasion, even Kyiv admits six Kinzhal ballistic missiles managed to elude its air defenses.

So what’s changed in the space of just a few weeks?

All about the Patriots?

The obvious answer, in the Kyiv region at least, is the deployment of the US-made Patriot air defense systems, which arrived in Ukraine last month.

The US and Germany have each supplied one Patriot battery to Ukraine.

Patriot interceptor missiles can hit high- and medium-altitude aircraft, cruise missiles and some ballistic missiles, according to the Center for Strategic and International Studies (CSIS).

So formidable are the Patriot defenses that Russia has pledged to take them out. Indeed, some experts believe this month’s wave of attacks has been designed specifically to overwhelm them with numbers.

And Tuesday’s attacks on Kyiv likely damaged, but did not destroy, one of Ukraine’s Patriot systems, a US official told CNN.

But it’s not the Patriots alone defending Ukraine’s skies.