GEOFF BENNETT: For more than 10 days, Iran has unleashed one weapon in particular at countries that host U.S.

troops.

Shahed drones have targeted American bases, killing U.S.

troops and hitting civilian infrastructure and energy facilities.

But long before they flew across the Middle East, Shaheds fired by Russia targeted Ukrainian troops and infrastructure.

We have two looks at the drone threat, starting with special correspondent Jack Hewson, one of the few foreign correspondents who reported from Kharkiv at the beginning of the full-scale invasion.

Jack returns to that Eastern Ukrainian city to meet frontline troops, who have more experience facing Shahed drones than anyone else.

JACK HEWSON: Kharkiv's air war doesn't begin in the city.

It starts out here in the fields and villages that lie between the front line and the regional capital.

We're on our way to a position about 20 kilometers from the Russian line in Izyum in Kharkiv province.

And, strangely, even though we're a long way from Kharkiv, the city itself, this is where air defense actually begins.

Shahed fly over this area in the direction of the city, and it's here that they're intercepted.

And it's also where they intercept Russian observation drones as well.

Notice the nets.

That's to protect cars like ours.

Making this journey more harrowing is the fact that short-range first-person view, or FPV, drones have hit vehicles here.

They have an expanded range and are now guided by fiber-optic cable to evade electronic jamming.

"ASKET," Ukrainian 115th Mechanized Brigade: Everything which is closer than 40 kilometers could be destroyed by Russian drones, by different types of drones, not only FPV drones but Lancet and a lot of other types of Russian drones.

JACK HEWSON: Drone and missile strikes, many launched from deep inside Russia have hit Kharkiv, Ukraine's most bombarded city, for years.

And it's only getting worse.

In addition to attack drones, Russian forces fly reconnaissance drones and longer-range Iranian-made Shaheds across this area and into Kharkiv city itself.

To counter, Ukraine has developed reconnaissance and interceptor drones of its own and pushed its air defense network out towards the front line, trying to intercept before they reach the city.

They operate from below ground, hiding from Russian recon drones like the ZALA and Orlan.

The latter is a direct threat to Kharkiv city, helping to guide missiles and Shahed drones onto their targets.

They also threaten frontline troops.

We blurred some images at the unit's request to protect the unit's operational security.

"SMILE," Drone Pilot, Ukrainian 115th Mechanized Brigade (through translator): The Orlan knocks out our units.

They knock out our people, our equipment.

They also actively knock out our artillery.

Due to its relatively powerful zoom, it has both optical and digital zoom.

It sees very far and it has the ability to help target both guided munitions and artillery.

It can target just everything.

JACK HEWSON: But one of the most difficult targets for these pilots is the Shahed.

KUCHERIAVYI, Drone Pilot, Ukrainian 115th Mechanized Brigade (through translator): Because it flies low and is very difficult to detect, plus the fall weather conditions, and it simply flies fast.

JACK HEWSON: Despite the challenges, Ukrainian crews are scoring hits like this one, but for every hit, many more slip through.

There is a constant race to keep up with each innovation and counterinnovation in tactics and technology between the Hunter and the hunted.

According to Commander Mer, the evolution continues and, as their crews adapt, so do the Russians.

"MER," Unit Commander, Ukrainian 115th Mechanized Brigade (through translator): Now the Shaheds are even being equipped with radio-electronic interference systems to interfere with our interceptor.

The enemy also plays with the altitude and at the same time he began to launch a much larger number of Shaheds in one group.

That is, before the group consisted of three or four enemy Shaheds.

Now this group, their number has increased to eight or nine.

JACK HEWSON: According to the commander, innovation happens primarily on the battlefield supported by start-ups and NGOs.

"MER" (through translator): The state can only provide what has already proven itself and has results.

What has proven itself and has results is no longer effective on the battlefield.

Such dynamics mean that we have to try.

We have to constantly put the latest technologies in place and gamble with what works.

JACK HEWSON: To understand what they're up against, the unit takes us to examine one of the drones they have recently brought down.

This one had a gasoline-powered propeller motor, allowing it to travel at up to 115 miles an hour, but newer models are presenting bigger challenges.

"AKUSHER," Ukrainian 115th Mechanized Brigade (through translator): Their warhead has from 40 to 50 kilograms of explosives, and they have already modified the design of the Shahed itself in the structure and are doubling the warhead.

I would also like to add that they are pioneering using jet engines.

True, they haven't been detected in our zone yet, but these are also their changes, their tactics.

JACK HEWSON: And with jet-powered Shahed coming to this war, with top speeds of more than 310 miles per hour, Ukraine's air defense teams will continue to have their work cut out.

For the "PBS News Hour," I'm Jack Hewson in Kharkiv, Ukraine.