GEOFF BENNETT: Since the start of Russia's full-scale invasion, the U.S. and its allies have supplied Ukraine with tens of billions of dollars of weapons systems and ammunition.

But keeping the material flowing for this bruising war is proving a challenge for arms manufacturers.

Nick Schifrin has the story.

NICK SCHIFRIN: The poets call war the ultimate measure of man.

Planners call war, the ultimate competition of logistics.

And it's been 80 years since a war with logistics on this industrial scale.

Ukraine fires as many 155-millimeter artillery rounds in about five days as the U.S. produces in a month.

Many of them are forged, finished at 1,500 degrees, and painted here, a 1950s factory in Scranton, Pennsylvania.

The machinery is decades-old, but, until now, it's suited us needs.

Iraq and Afghanistan were not dueling artillery battles.

But, today, the 20,000 artillery shells the plant creates every 30 days is a fraction of Ukraine's needs.

Ukraine's defense minister, Oleksiy Reznikov, recently wrote to the European Union in a letter described to "PBS NewsHour" that Ukraine can only one-fifth of what it could because of munition shortages.

We saw that ourselves on the outskirts of Bakhmut in Eastern Ukraine.

This team told us they did not have enough artillery to fire constantly.

Olexander commands and artillery unit in the 93rd Brigade.

Do you have what you need in order to complete this fight?

SENIOR SGT.

OLEXANDER, 93rd Brigade (through translator): We do have equipment, but we need more, and we need more and more and more, because they won't stop until we stop them.

JENS STOLTENBERG, NATO Secretary-General: The current rate of Ukraine's ammunition expenditure is many times higher than our current rate of production.

NICK SCHIFRIN: Last month, NATO Secretary-General Jens Stoltenberg said defense industry couldn't deliver fast enough and had to expand quickly.

JENS STOLTENBERG: This is now becoming a grinding war or attrition.

And the war of attrition is a war of logistics.

SETH JONES, Center for Strategic and International Studies: The U.S.' defense industrial base is not fully prepared to conduct an industrial-style war or to deter that kind of war.

NICK SCHIFRIN: Seth Jones directs the International Security Program at the Center for Strategic and International Studies, and recently wrote a report about a shortage of materiel, empty bins in a wartime environment.

SETH JONES: The U.S. has had operational plans for a major war, but I think what hasn't happened is to tie those plans directly to acquisitions needs right now.

NICK SCHIFRIN: Already, the U.S. has sent from its stockpiles more than $32 billion worth of weapons, including more than a million 155-millimeter shells, 1,600 shoulder-fired Stinger anti-aircraft missiles, 8,500 Javelin anti-tank weapons, 1,800 Phoenix Ghost drones and 38 High Mobility Artillery Rocket Systems.

SETH JONES: What the U.S. has been able to do is use a range of its stockpiles of weapons.

The challenge, though, is that a number of those stockpiles are now decreasing, and the production lines aren't rising to levels that we need them for future contingencies.

NICK SCHIFRIN: It's not only about Ukraine.

The military always plans for contingencies, including a war in the Pacific with China.

And now the Defense Department is spending billions to increase production, including modernizing the Scranton plant, as seen in these before-and-after photos.

Already, production has increased nearly 50 percent.

Overall, the Army hopes to increase artillery production 500 percent in the next two years, the largest production expansion since the Korean War.

Bill LaPlante is the undersecretary of defense for acquisition and sustainment.

I spoke to him on Wednesday, and began by asking him whether the West could meet Ukraine's needs for artillery.

WILLIAM LAPLANTE, U.S.

Undersecretary of Defense for Acquisition and Sustainment: We will do our best and we have been doing our best to meet the demand as it comes in.

And, of course, the devil's in the details as to which caliber.

But, yes, the piece showed, on the 155-millimeter, we have already funded the factory at significant amounts to get that production rate ultimately up at five times that amount, which is almost unprecedented.

And it's not just producing, but what we're also buying and getting from around the world in different stocks to supply what the Ukrainians need.

Every day, we try to move something to the left, whether it's finding equipment in another country we can ship in, or anything we can do to find stocks.

NICK SCHIFRIN: As we just saw Ukrainian soldiers just a few weeks ago outside of Bakhmut told me they didn't have enough.

That was an artillery piece, an older artillery piece, Soviet era.

WILLIAM LAPLANTE: Right.

NICK SCHIFRIN: I was with another mortar unit.

They said they didn't have enough mortars, also firing Soviet era mortars.

This isn't only about American and European weapons, is it?

WILLIAM LAPLANTE: Right.

NICK SCHIFRIN: It's also about getting Ukraine older weapons, which many of their units still use, right?

WILLIAM LAPLANTE: That's exactly right.

It's a constant challenge of, do we find or produce the old Soviet or Russian equipment?

Or do we give them the new equipment?

And that's -- we go through that every day.

NICK SCHIFRIN: But on air defense, specifically, I have been told they're running out of S-300 parts, weapons all over the world.

And so, therefore, they have to go to Western... (CROSSTALK) WILLIAM LAPLANTE: I think, for air defenses, and, frankly, for ground forces, what you're seeing is having to go from the old Soviet systems to almost certainly Western systems for the reasons you said.

NICK SCHIFRIN: And this is all, of course, before we get to Ukraine'S spring offensive.

You are trying to figure out how to get all these armored vehicles and their parts into Ukraine.

How do you know that they will have enough of those munitions, those parts, those modern weapons to be able to launch some kind of counteroffensive in the coming weeks?

WILLIAM LAPLANTE: What we're doing is working with the Germans, the Poles and the other countries, when we have a shortfall in parts, say, for a certain version of Leopards, to scour and find those parts, even to the extent we can find advanced manufacturing or 3-D print.

So we're working on each one.

And the idea is to make sure that there are enough parts to sustain for each model.

NICK SCHIFRIN: Why not give Ukraine the longer-range weapon known as ATACM, which would fly 180 miles, that it's been requesting?

So far, the administration has refused.

WILLIAM LAPLANTE: Yes, it's been a policy decision to date that the long-range weapons, which we have been providing, which is about an 80-kilometer precision-guided weapon, is sufficient in range for the targets that they have.

I think for -- when you get into types of capabilities that are well beyond it, you get into policy issues and sustainment issues of whether or not it's an escalatory thing.

NICK SCHIFRIN: If I could, though, intelligence officials tell me that, specifically, the capacity of the ATACM and the range of the ATACM is a red line for the Kremlin in terms of what Ukraine would be able to hit if it were to use that weapon in Russia.

But why is that a concern, given that Ukraine has promised not to use American weapons inside Russia?

WILLIAM LAPLANTE: Well, I think it's one of the concerns.

I think there's multiple concerns.

And the other piece of it is what -- to what extent it will make a big difference in the battle.

And those are all part of the calculation.

NICK SCHIFRIN: To what end are you trying to procure weapons for Ukraine to reseize all of its territory that it has lost since 2014?

WILLIAM LAPLANTE: We're providing everything we can that we believe they need.

And I would say this.

We are going to be there with them until it's over and as long as we need to, and not for the least of which is, if we think it's expensive now, if Putin prevails, it'll be really expensive.

And so this is really that important.

And we were going to provide the equipment they need.

NICK SCHIFRIN: Ukraine argues it won't be over until it reseizes Crimea.

WILLIAM LAPLANTE: That may be their view.

NICK SCHIFRIN: And that's Ukraine's choice, basically?

That's the U.S. policy.

WILLIAM LAPLANTE: This is their fight.

This is their fight.

NICK SCHIFRIN: You heard Seth Jones in the package there saying that, as stockpiles in the U.S. are being drawn down, production lines aren't expanding enough to meet future requirements.

Do you agree?

And, if so... (CROSSTALK) WILLIAM LAPLANTE: I think that that's a subjective comment.

I actually -- I actually don't necessarily agree.

I think we're going across the board and putting billions of dollars in investment across -- across in these companies.

And it's going to be rapidly ramping up.

And so, really, what's at stake here is a time issue.

It's, we will rank up -- ramp up, and we are ramping up right now.

And the question is -- arguably, is racing against time.

and that's where -- that's where we are.

NICK SCHIFRIN: How does that translate, though, into actual deliveries?

How long does that take?

WILLIAM LAPLANTE: Right.

This gets to something called a long lead item, how long it takes before you get the item when you actually award it.

And so what -- what that can be, as long as a year.

But it's every day we have teams working on this, scouring the earth.

NICK SCHIFRIN: And, finally, how do you prioritize orders, especially moving forward?

You have argued that the weapons going to Ukraine do not affect some of the weapons orders, for example, that Taiwan is making.

But the fact is, the U.S. is behind on some of the orders it has promised to Taiwan.

WILLIAM LAPLANTE: Right.

NICK SCHIFRIN: So what is that priority?

And does one theater affect the other?

WILLIAM LAPLANTE: It can affect.

But there's less overlap, perhaps, than people believe.

I will give you the example for Taiwan.

There is a backlog for Taiwan.

It happens to be on items like F-16 and production of F-16.

That's a lot of it, which, to date, even though there's been discussions, hasn't been a player in the Ukraine.

Where I will say that there is something that we all have to watch is the underlying suppliers, the suppliers of solid rocket motors, of batteries, of energetics.

There, those are common across all domains.

And that's where we have also been putting our emphasis.

NICK SCHIFRIN: And what is -- what message does your struggles to deal with the procurement challenges right now and also what you're doing to overcome them, what message does that send to China when it comes to Taiwan?

WILLIAM LAPLANTE: Well, I think what we -- I like to think that what we show China is, number one, we can turn fast.

We can turn fast.

We are getting folks under contract within a week.

And we are getting things put together and into theater that are incredibly innovative very, very fast.

We will follow up and make sure our industrial base is ready to go.

And so I have often said that industrial capacity is itself a deterrent.

And so I think we have to remind ourselves that as we look not just to China, but at what's beyond Ukraine.

NICK SCHIFRIN: Bill LaPlante, undersecretary of defense, thanks very much.

WILLIAM LAPLANTE: Thank you Nick.