AMNA NAWAZ: As we approach the one-year anniversary of Russia's full-scale invasion of Ukraine, a look at the ground war and the front lines.

Ukraine and the U.S. say Russian forces have launched offensives in three areas of Ukraine's Eastern Donbass region.

With support from the Pulitzer Center, Nick Schifrin and videographer Eric O'Connor visited all three parts of the front, starting at one of the most southern points on the front line, Novosilka.

And a warning: Some images in this story are disturbing.

NICK SCHIFRIN: The road to Ukraine's 1st Tank Brigade front-line position is bumpy and tense.

We're escorted by a sergeant, who tells us to stay low and move fast.

OK, let's go.

Trees provide the best cover.

Our guide calls ahead about our position using code words.

They refer to us as ants.

And so we go marching in single file on the same path Ukrainian soldiers take past the craters.

The Russian line is only a mile-and-a-half.

Stop.

Get down.

We have just heard an explosion nearby, so we are just a little taking cover.

Right now, we're trying to walk along the tree line, so that we're not too visible.

Trying to get to these Ukrainian trenches down the road here.

How are you?

Trees may conceal, but don't protect from the incoming.

The trench is the safest defense.

Ukraine's front line is 700 miles' long, this trench, just one small section, 1,000 feet, eight-feet-high, and where this unit has deployed for 3.5 months.

Ihor is the platoon commander.

He joined the military in 2014 after the initial Russian invasion.

He was recalled a year ago this week.

IHOR, Platoon Commander, 1st Tank Brigade (through translator): They're trying to attack our direction and to push through our defenses.

And we are not letting them do that.

We are holding our position.

We're doing everything possible to not let this happen.

NICK SCHIFRIN: Have they launched frontal assaults against these trenches?

IHOR (through translator): With small groups, three to four tanks and infantry.

They are attacking with artillery, as you can hear.

Their artillery is working.

That's how they do it.

NICK SCHIFRIN: Ukraine's infantry is tasked with the always vital, sometimes terrifying mission of holding the line.

Not all of them have made it.

IHOR (through translator): We have had wounded.

We have had killed.

It's a difficult subject.

I don't want to talk about it.

Translate that.

NICK SCHIFRIN: You don't want to talk about it.

IHOR (through translator): It's difficult to talk about.

I don't want to talk about it.

Any other questions?

NICK SCHIFRIN: Ihor lives where he fights.

He tries his best to keep out the cold.

Everyone here seizes a quiet moment when they can.

He has faith that Ukraine can win, but he predicts it will take years.

IHOR (through translator): The world should know that, while we're fighting the enemy here, the world is safe.

And the whole world should help us with everything they can and provide us with weapons to ensure this doesn't happen in their countries.

We're capable of stopping the enemy here.

Just give us the weapons.

NICK SCHIFRIN: Tanks are this unit's primary weapon.

The region is flat.

For Kyiv to have any chance to push through Russian lines, it says it will need more modern tanks.

But 26-year-old Yehor's T-64 tank was originally built in the 1970s.

JUNIOR SGT.

YEHOR, 1st Tank Brigade (through translator): They are old.

And because they are old, they break all the time.

You don't have confidence that your tank is going to work tomorrow.

For us to advance, we need new weaponry, because these tanks are twice as old as I am.

NICK SCHIFRIN: Until new weapons arrive, all this unit can do is use it's armor like it uses its trenches, to hold the line against a larger Russian force.

JUNIOR SGT.

YEHOR (through translator): In order to destroy the enemy and be more effective in our offensive, we need heavy weapons.

Without tanks, we're not doing anything right now.

It's not easy to destroy a stationary firing position, even a machine gun.

NICK SCHIFRIN: And Russia has a web of stationary positions.

They still control 20 percent of Ukraine.

And they have spent months digging in.

Russian trenches, vehicle barriers, and tank traps fill Ukraine's south and east.

They run all the way up to the northern part of the eastern front, where we visited next.

Russia controlled this land just a few months ago.

So, to prevent a Ukrainian counteroffensive, they mined the fields that we drove through.

MAN: Which direction is the Russians?

WOMAN: In front of us.

NICK SCHIFRIN: The 103rd Brigade's mortar unit positions itself as close as possible to Russian troops and as deep into a forest.

The more isolated, the harder to target.

The commander is a 46-year-old whose call sign is Kalina, a berry on Ukraine's coat of arms.

The front line here hasn't moved an inch since they arrived nine months ago.

Do you have the weapons you need to be able to fight effectively?

KALINA, 103rd Brigade (through translator): No.We don't have enough weapons.

We don't have a large enough caliber.

The largest that we keep is 82 millimeters, and we need at least 120 millimeters.

We keep telling our commanders about this, but, right now, no one is providing those to us.

NICK SCHIFRIN: They have been fighting for one year, but that doesn't mean it feels normal.

Their patch is the Lviv lion, Kalina's hometown in the country's far west.

Did you think you would still be here one year later?

KALINA (through translator): No, I have never thought I would spend so much time here.

I'm not young.

I'm not fit for the army.

I thought they would just train me and let me go home.

But it all happened in a different way.

And now were here.

NICK SCHIFRIN: They use drones to spot Russian targets, and then 20 rounds in about three minutes.

They adjust the mortar back to the original target and repeat.

But they admit they're limited by the quantity and quality of their ammunition.

And that means the best this unit can do as well is hold the line against the Russian troops they continue to target.

The next day, we headed to the outskirts of Russia's primary goal, Bakhmut.

U.S. officials downplay the city's importance, and have raised with Ukraine falling back to higher ground to defend larger cities.

But Ukraine calls Bakhmut a symbol of resistance and a gateway to the rest of Donetsk province.

The city has been largely abandoned or destroyed.

And the fighting has been fierce, targeting Russia's paramilitary Wagner Group.

The U.S. assesses it has taken 30,000 casualties.

Wagner's owner, who's close to Putin, posted this photo this morning identifying the bodies as those killed just yesterday.

The Ukrainian soldiers fighting for back out have witnessed some of the most brutal battles of the last year.

SENIOR SGT.

OLEXANDER (through translator): They are sending their soldiers as cannon fodder.

We target their equipment and their soldiers, but they keep coming and coming and keep dying and dying and even then keep coming and coming.

NICK SCHIFRINI: Olexander leads a 93rd Brigade artillery unit.

There are other units with more advanced equipment, but the vast majority are like this one.

Their self-propelled artillery is also from the 1970s.

The brigade gave us this video from a surveillance drone of what it said was its artillery hitting its target.

They and everyone here say the commute is worth it.

Senior SGT.

Olexander: This place is strategically important.

But first and foremost, this is our land.

And every inch of our land is of the utmost importance because people are dying for it.

If we give up, Bakhmut, we would be giving up so many lives of those who've been defending it for such a long time.

NICK SCHIFRIN: Have you lost men?

Have you lost friends?

Senior SGT.

Olexander (through translator): We've all lost someone in this war.

And keep losing.

That's how it goes.

This is war.

Senior You can't do anything about it.

But these are all losses that cannot be prevented.

They just happen because people kill people.

That's it.

NICK SCHIFRIN: On the front lines.

Ukraine knows the price it will continue to have to pay, how many men it will continue to lose.

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