Introduced in 1981, the Patriot originally had a shelf life of 15 years. As that limit approached the existing missiles were examined and it was determined that those that had various age-sensitive components (batteries, rocket motor, and most electronics) replaced before they reached their useful life could be re-certified to last another 15 years. Now older missiles have again been re-certified and some of the 100,000 missiles built since the 1980s can be kept around for 45 years. The refurbishment also includes using new technology to accurately measure age-related decay in many components. This is an important aspect of being able to extend shelf-life in missiles and aircraft.
When elderly components are replaced, it is often with improved versions of the aging component. This is particularly true with the electronics, which are most subject to upgrades. This continuous upgrading makes it worthwhile to keep older Patriot missiles in service over a long period of time. Most missiles are never fired and are eventually deemed too unreliable for use and are taken apart for scrap and reusable spare parts. About five percent of the Patriot missiles built have been used for testing and less than a hundred in actual combat. The missiles are stored and fired from a protective container, which can be plugged into diagnostic equipment for regular testing. In addition to the United States, another twelve nations use Patriot.
The current version of the original Patriot missile design (MIM-104E PAC 2) cost $2 million each and can be used against aircraft and missiles. The smaller PAC-3 (MIM-104F) anti-missile missile can only be used against missiles and can cost up to $3 million each.
The U.S. Army has ten Patriot anti-aircraft missile battalions. Each Patriot battalion has 12-24 launchers (in 3-6 batteries). Each battery is manned by about a hundred troops and contains a radar, plus four launchers. A battery can fire either of the Patriot missile types. The PAC-3 missile is smaller than the anti-aircraft version (PAC-2), thus a Patriot launcher can hold sixteen PAC 3 missiles, versus four PAC-2s. A PAC 2 missile weighs about a ton, a PAC-3 weighs about a third of that. The PAC-3 has a shorter range (about 20 kilometers) versus 70 kilometers for the anti-aircraft version. Kuwait has some Pac 3 missiles but is apparently mostly concerned with air attacks.
While each Patriot launcher, loaded with PAC-3 missiles, can only defend against ballistic missiles approaching within 20 kilometers, the Patriot radar can detect targets out to a hundred kilometers. Two PAC-3 missiles are fired at each incoming ballistic missile, to increase the probability of a hit. The PAC-3 missile has its own radar and uses it to track the incoming warhead and execute a collision course.