AMNA NAWAZ: This week, we will mark one year since Russia's full-scale invasion of Ukraine with a series of stories, tonight, the drone war.

Nick Schifrin and videographer Eric O'Connor recently traveled to front-line units in Donetsk province and report on Ukraine's effort to modernize a war that's often seemed an echo from last century.

NICK SCHIFRIN: In the forest outside Bakhmut, where two soldiers fight on their own, the sounds of war have not changed for centuries.

The Ukrainian soldiers fight with the weapons of yesterday and today.

They launch their $10,000 Chinese drone up and over the trees they use for cover to hunt for Russian troops.

It's the 21st century version of forward observing.

The drone locates a Russian target and relays its location to the brigade's artillery commander.

Before the war, the 33-year-old pilot was an engineer, which is his nickname that he asked us to use.

ENGINEER, Drone Pilot: Commander over artillery sees this screen too, like, monitor all the time.

And from different angle from different drones, they can react fast and quickly.

It takes approximately three to five minutes.

NICK SCHIFRIN: Three to five minutes from the time that you spot them until the time they can fire.

ENGINEER: Yes, yes, even faster.

NICK SCHIFRIN: We're about a mile-and-a-half here from the front line.

We have heard distant artillery, even small arms, all morning.

And this drone, it's just the two of them operate completely isolated separate from their unit.

They call their drone an angel in the sky.

On this day, his drone filmed as a Russian helicopter fired on Ukrainian troops.

But he gave us other videos from the battle of Kherson, where he called in the location of Russian tanks so one could be hit with a Ukrainian strike.

ENGINEER: They have weapons, have tanks.

And we are, like, looking for like our mission to find and give coordinates.

Easy to say a lot.

A little bit harder to be seen.

NICK SCHIFRIN: In wars gone by, snipers hunted for other snipers.

In this war, drone pilots hunt each other.

While you're using drones on the Russians, are the Russians using drones on you?

ENGINEER: Yes.

Yes.

They're looking out for us too.

And it's like huge luck if you find another pilot.

Sometimes, we are hunting at each other, because if you are not able to see what is the situation, you are not -- your artillery is done.

It's not working.

NICK SCHIFRIN: You're blind.

ENGINEER: Yes.

Yes.

NICK SCHIFRIN: So when you're not flying, you sleep in the bunker.

ENGINEER: Yes.

Yes, we sleep in the bunker.

NICK SCHIFRIN: They have been using this location for months, thanks to this bunker they happened to cross.

He shows us some Ukrainian hospitality, thanks to a butane stove and some bottled water.

ENGINEER: The quick way to make tea.

NICK SCHIFRIN: He shows me how Ukrainians try to detect Russian drones.

The Russians have their own countermeasures.

ENGINEER: And it automatically detect your drones and shut down your signal.

(CROSSTALK) NICK SCHIFRIN: Oh.

So, it's jammers.

ENGINEER: Yes, it's really harmful when you lost your drone.

It's like you're losing a friend, maybe, I will say, really sad moment, because it's like you have had some connection.

I would say you -- it's like your partner.

Yes.

Yes.

NICK SCHIFRIN: Some partners have been around longer than others.

This Ukrainian drone model has been flying since Russia's initial 2014 invasion.

It's not as fancy.

It specializes in photos, but its operators consider it older and wiser, much like they consider themselves.

Their unit name loosely translates to Old Fogies; 59-year-old commander Igor was retired and volunteered the day of the invasion.

IGOR, Drone Unit Commander (through translator): At the start of the war, the Russians had more artillery and drones.

But now this balance has changed.

And I can feel it every day.

And we're better.

NICK SCHIFRIN: Vitaly, the pilot, is 51.

He grew up in far western Ukraine flying model airplanes.

VITALY, Drone Pilot (through translator): Ever since I was 6, my hobby was airplane modeling.

So, in 2015, when I was called up, I understood that I could contribute the most by becoming a drone pilot.

NICK SCHIFRIN: They're far from the main road, but not from the artillery that they're helping to aim.

Each surveillance flight lasts about an hour.

The only way to know what the drone has seen is by manually opening it and removing into memory card, which promptly goes into the van.

We can't show the screen right now, but you're looking through photos that the drone has taken to reveal Russian locations.

What can you do with those photos.

VITALY (through translator): It gives us information of quantity of military equipment, type of military equipment, and this gives us the ability to decide to target immediately with the help of artillery or take additional actions.

NICK SCHIFRIN: To send their images and guarantee communications, they rely on Starlink owned by SpaceX CEO Elon Musk, despite SpaceX threats to cut them off.

IGOR (through translator): I think that Elon Musk is part of our crew, our team, so I don't think that he will block it.

And we can constantly feel his support.

NICK SCHIFRIN: Does the use of drones go both ways?

Is it like a cat-and-mouse game?

IGOR (through translator): We don't see significant changes in Russian drones, except for the Iranian Shaheds.

NICK SCHIFRIN: That's a reference to Iranian-made Russian attack drones.

They have struck the country's infrastructure and alongside Russian missiles have challenged Ukraine's air defenses.

Senior us and NATO officials tell "PBS NewsHour" Ukraine will run out if its mostly Soviet era air defense within months.

So, the West is building a Western-only air defense system, including American Patriots, the national advanced surface-to-air missile system, the same system that defends Washington, as well as European systems, including from Germany and France.

President Volodymyr Zelenskyy said this past weekend it would work.

VOLODYMYR ZELENSKYY, Ukrainian President (through translator): I believe that, today, in terms of air defense systems, we are probably at the best level since our independence.

NICK SCHIFRIN: But back in the van near the front, the team using old Ukrainian technology believes the West needs to accelerate its assistance.

VITALY (through translator): It would be nice if Europe and America would try and help finish this war as soon as possible, because it's up to them how quickly we can evict the invader from our land.

NICK SCHIFRIN: They have no faith that can be accomplished soon, so they prepare for the next mission and help their comrades fight a grinding ground war with their eyes in the sky.

For the "PBS NewsHour," I'm Nick Schifrin outside Bakhmut, Ukraine.