GEOFF BENNETT: As Kyiv burns night after night, Ukrainians are desperate for more missile defense systems to repel Russia's relentless onslaught of drones and ballistic missiles.

For the missiles in particular, no system is more valuable than the U.S.

Patriot interceptor.

But years of use by the Ukrainians and by the U.S.

in the war with Iran have depleted thin stocks.

Special correspondent Mike Cerre has this exclusive look at the Patriot manufacturing process, and also from the ground in Ukraine, where their need is so acute.

(SIRENS BLARING) MIKE CERRE: It's now 4;15 in the morning in Kyiv, and we're hearing the sirens for the first time.

But, earlier, we have heard three sets of explosions and the warnings to get to the bomb shelter, which has become a normal pattern here in Kyiv.

The hotel bomb shelter was a new experience for this group of American relief volunteers on their very first night in Kyiv, especially for volunteer Richard Bew, who works for Lockheed Martin, the major defense contractor that builds the Patriot interceptor missiles the Ukrainians need every day and can't get enough of.

You sure you don't have an extra Patriot in your backpack?

RICHARD BEW, Lockheed Martin: I think we just spent a couple of them just now, but it sounds like they did their job.

MIKE CERRE: Richard Bew was one of 30 American volunteers on this Ukrainian relief convoy organized by AIDed.org delivering emergency vehicles and critical technology equipment for frontline Ukrainian units.

Along the way, they got a better understanding of the nightly and deadly surge in Russian airstrikes that accelerated with reports of a global Patriot shortage.

We were required to obscure the faces of Ukrainian security on the convoy.

RICHARD BEW: So, last month, we made more Patriots than we did the month before, and more Patriots than we did the month before that, and next month, we're going to make more than we did this month.

MIKE CERRE: We caught back up with Richard Bew at Lockheed Martin's missile production headquarters in Grand Prairie, Texas, where he reported back to the company on what he learned.

It can take more than a year and an estimated $3 million to $4 million to make a single Patriot missile, according to Lockheed officials.

To reduce the shortages, Lockheed Martin is expanding its facilities, work force, and creating joint ventures in other industries to maintain its supply chain of components, which make up more than half of a missiles assembly.

RICHARD BEW: This is what's going to allow us to go from 400 to 600 historic demand per year for a Patriot upwards of 2,000 by 2030.

MIKE CERRE: That's 2,000 Patriots total, however the U.S.

allocates them.

The Ukrainians and American forces in the Middle East have reportedly used up that 2030 production target amount in just the past year.

TIM CAHILL, Lockheed Martin Missiles and Fire Control: This has been a problem that's been brewing for a long time over many years, as we have recognized that warfare is changing and the number of interceptors you might need for a prolonged conflict is becoming larger and larger.

MIKE CERRE: Tim Cahill, president of Lockheed Martin's missile and fire control business, thinks a new, cheaper version of the Patriot, the PAC-3 ACE, is easier to build and can help close the supply and demand gap.

TIM CAHILL: PAC-3 ACE is designed to be in aggregate about two-thirds performance for about half the price, fits right into a Patriot unit, designed to go after targets not quite as threatening as the current PAC-3 version.

MIKE CERRE: Other alternatives include using even less sophisticated reconfigured weapon systems to address the Russians' new rocket-powered Shahed drones.

RICHARD BEW: It's not going to go after your ballistic or hypersonic missiles.

You're going to use your PAC-3 MSEs for that.

But this is going to get what is now becoming the predominant threat and strike weapon in places like Ukraine and others.

MIKE CERRE: Lockheed has also developed a new drone interceptor like this one that can take down multiple drones at a time, which could be deployed on a limited basis to Ukraine or the Epic Fury campaign in Iran by the end of the year.

SETH JONES, Center for Strategic and International Studies: What we're seeing with the war in Ukraine and what with the U.S.

expenditure of munitions in Operation Epic Fury, that the U.S.

services made a major mistake in not building up munition stockpiles, and it has put the U.S.

military in the hole that it now sits in right now.

MIKE CERRE: Seth Jones, with the Center for Strategic and International Studies and a former Department of Defense official, has written extensively about the U.S.'

steady loss of its weapons surge capacity since the end of the Cold War.

SETH JONES: You can't deter an adversary if you don't have sufficient stockpiles.

So I think it's highly unlikely that the U.S.

is going to be giving a lot of its current inventory of Patriots to the Ukrainians.

That's the -- and the U.S.

actually also needs them for its own homeland defense.

MIKE CERRE: While in Ukraine, Richard Bew and the other American volunteers saw how the Ukrainians are trying to close the armed supply gap by making their own, and were briefed by Ukraine military brigade commander, who did not want to be identified, on what they now need to hold off the Russians.

What was your biggest takeaway being on the ground in Ukraine, spending a few nights in a bomb shelter?

What did you take, bring back here from that experience?

RICHARD BEW: This conflict has changed character several times.

If you remember, in the initial invasion, everybody thought it was going to be a three-day war and Russia was going to roll over Ukraine.

Taking a look at what happened.

Ukraine used Javelin missiles, right, to stop the convoys of Russians at the beginning.

We need to be anticipatory to make sure that what demands come next we're already working on.

MIKE CERRE: With no end in sight for either the Ukraine war or armed conflicts throughout the Middle East, the Ukrainians are likely to be spending many more long and anxious nights under the Russian siege from above.

For the "PBS News Hour," Mike Cerre, Kyiv, Ukraine.