Since Russia's invasion of Ukraine earlier this year, NATO members have engaged in a sort of musical chairs of military hardware. This is often the case when one ally sends weapons to Ukraine, a process known as backfilling, but also within the Western alliance itself.

Germany's announcement that it has offered its own Patriot missiles to Poland is the latest in that shifting of NATO resources, largely towards its Russia-facing eastern flank.

"Poland is our friend, ally and, as a neighbor of Ukraine, especially exposed," German Defense Minister Christine Lambrecht said on Monday (21.11.2022), following a call with her Polish counterpart.

Patriots: one-stop air defense

Poland's exposure to the war made itself felt earlier this month, when a missile landed just inside its borders. It was likely a Ukrainian one gone astray, not a Russian-launched projectile, Polish and other NATO officials have said. But the incident, which killed two people, marks the first time that weapons used in the nine-month conflict struck a third country.

Depending on the type and trajectory of the missile that landed, the Patriot air defense system could have stood a chance at intercepting it.

The Patriot has a long history. It was conceived in the early 1960s, but took its current name and shape a decade later. The US Army began to deploy the system — a collection of radars, command-and-control units, and various missile interceptors — in the 1980s.

The US weapons giant, Raytheon, produces the Patriot and has upgraded its capabilities several times since. The company says it plans to keep up with technical developments through at least 2048. In its current iteration, the Patriot can defend against tactical ballistic missiles, cruise missiles, drones, aircraft and "other threats" that Raytheon does not specify.

These are some of the airborne objects that Russia targets Ukraine with, and the ones NATO worries about in regards to its own territory. However, Russian forces also use smaller devices, such as mini drones that keep closer to the ground, which are more difficult for the Patriot system to track and intercept.

The system covers an area of around 68 kilometers (42 miles), according to the German military. Its radar can track up to 50 targets, and engage five of them at once. Depending on the version in use, the interceptor missiles can reach an altitude of more than 24 kilometers and hit targets up to 160 kilometers away.

Each unit requires about 90 troops to operate, according to the Center for Strategic and International Studies, a US think tank.

A battle-tested system

Poland is no stranger to the Patriot. It is one of 18 countries using or looking to acquire the air defense system. The United States delivered units to Poland shortly after Russia's invasion of Ukraine, and Poland has requested to buy more.

Germany has 12 such units, according to media reports, and has stationed two of them in Slovakia. The specifics of the Poland deployment are up to the two countries' defense ministries.

The Patriot has seen combat. Its first real-life use was in 1991, when defending US and coalition troops, as well as populated areas in Israel, against Iraqi Scud missiles during Operation Desert Storm. At the time, US and Raytheon officials touted the Patriot's efficacy. Outside research later questioned those claims.

In the deadliest incident, a Scud attack killed 28 US troops in their barracks in Saudi Arabia when the Patriots protecting them failed to intercept the incoming missile.

Subsequent upgrades have improved the system's usefulness. It was deployed, to greater effect, again to Iraq in 2003 during the US-led war there. A number of test launches since have resulted in successful interceptions, although multiple Patriot interceptors are often needed to stop a single incoming threat.

The biggest challenge to the Patriot may not be keeping up with enemy technology, but the cost of doing so. Poland's first Patriot procurement was reported to have cost $4.75 billion (€4.63 billion) — more than one-quarter of the country's proposed 2023 defense budget. A single interceptor test, according to RAND, a US-based defense research group, can cost up to $100 million.

Many of the threats the Patriot faces, such as drones, cost a small fraction of that. To help spread costs, some NATO allies agreed in October to jointly address their air-defense needs, including the purchase of more Patriot units.

Edited by: Rob Mudge