The U.S. said on Wednesday that it would supply Ukraine with the powerful Patriot air defense system to help it withstand Moscow's persistent air attacks.

But what exactly are Patriot missiles and why does Ukraine need them?

Patriot is a backronym for Phased Array Tracking Radar to Intercept of Target.

According to an anonymous White House official, the Patriot air defense system "will be a critical asset to defend the Ukrainian people against Russia's barbaric attacks on Ukraine's critical infrastructure."

Raytheon's MIM-104 Patriot is a surface-to-air missile (SAM) system designed to intercept high-flying aircraft.

Patriot systems are available in completely mobile batteries with a command center, a radar station to identify oncoming threats and launchers. The current interceptor missile for the Patriot system costs roughly $4 million every round, according to the US-based think tank Center for Strategic and International Studies (CSIS), and the launchers cost about $10 million each.

With the Patriot system, five targets can be engaged simultaneously using its radar, which can track up to 50 targets. Depending on the variant being used, interceptor missiles have a maximum altitude of 2 kilometers and a range of 160 kilometers.

According to Raytheon, system updates will last at least until 2048. The company's current Patriot batteries can protect against drones, planes, tactical ballistic missiles, cruise missiles, and "other threats" that it does not name.

These are a few of the airborne weapons Russia has in its arsenal to attack Ukraine. The Patriot system, however, has a harder time tracking and intercepting some of the smaller weapons used by Russian forces, such as miniature drones that hover closer to the ground.

Why does Ukraine need such weapons?

Zelenskyy urged leaders to deliver more air defense weaponry during a recent Group of Seven (G7) meeting.

"Unfortunately, Russia still has the advantage in artillery and missiles," he said.

Ukrainian Foreign Minister Dmytro Kuleba stated in late November that the Patriot defense system is "what Ukraine needs the most" to secure electricity infrastructure and prevent blackouts.

"We need air defense, IRIS, Hawks, Patriots, and we need transformers," he said from the sidelines of a NATO meeting in Bucharest.

Ukraine has used a variety of systems to counter Russia's cruise missiles and bomb-like Shahed-136 drones, but modern SAM system launchers and missiles, including NASAMS, are scarce.

International supporters of Ukraine want to see the country build multi-layered air defenses that include low, medium, and high-altitude systems that can protect against a variety of threats.