- [Narrator] This is the US-made Patriot Air Defense System.

Since two were delivered to Ukraine in April,

it's proving to be an indispensable tool in Kyiv's arsenal.

That's because the system

is defending Ukraine's ground troops,

cities, and critical infrastructure,

amid a barrage of Russian attacks.

So why does the Patriot have an advantage

over other air defense systems?

Let's break it down.

"At the start of the war,

Ukraine relied on a stockpile of Soviet-era defense systems.

Those weapons can target slower-moving aerial targets

such as drones and cruise missiles,

but they've struggled to combat

faster-moving ballistic missiles.

Now, Patriot systems are helping Ukrainian forces

to intercept those projectiles,"

and that's according to a Ukrainian Air Defense Commander

interviewed by "The Wall Street Journal."

(speaking in foreign language)

- Narrator] Here's how it works.

Patriot missiles consist of multiple components.

Three of its main parts sit on top of truck platforms.

The radar tracks missiles and other targets.

It can detect aircraft up to 62 miles away

and ballistic missiles more than 100 miles away.

It sends data to the engagement control station,

that unit then processes the information

before sending it to the launching station,

which can carry up to 16 missiles.

(speaking in foreign language)

- Narrator] Military analysts say,

"The system has outperformed

initial expectations in Ukraine."

(speaking in foreign language)

- [Narrator] Also known as the Kinzhal,

the Kh-47 is one of Russia's most advanced weapons.

On May 16th, a Patriot detected

six Russian Kinzhal ballistic missiles

at a distance of around 125 miles.

The system launched interceptors

destroying all of them.

Patriots in Ukraine fire at targets

using two different types of interceptors,

PAC-2 and PAC-3.

PAC-2 downs targets through blast fragmentation,

and PAC-3 uses hit-to-kill technology instead.

By combining the Patriot with other air defense systems,

Ukraine is now fending off most aerial threats against Kyiv.

However, the Patriot does have some disadvantages.

It's by far the most expensive single weapon system

that the US has supplied to Ukraine.

Each Patriot system costs around $1 billion

and takes two years to build. (missile blasting)

The missiles fired out of the Patriot are expensive too.

Each PAC-3 costs around $4.1 million.

The high cost per missile

and the relatively small number of missiles in a battery

means that Patriot operators cannot shoot at every target.

In addition, the Patriot requires a lot of manpower.

The systems need as many as 90 soldiers to operate,

but the control station can be operated in the field

by as few as three.

Gaining more batteries could help Kyiv

in a number of ways amid a counter-offensive,

namely, being able to protect ground troops

from aerial threats as they push to retake territory.

This summer, the US announced a new military package

worth up to $500 million.

"The aid will include ammunition for Patriot systems,"

according to a statement from the Pentagon.

There are at least two full Patriot systems

operating in Ukraine.

In July, Germany announced it would provide

two additional Patriot Missile Launches.

Ukrainian President Vladimir Zelensky

has said, "The country wants as many as 50."