As well as the USA, Patriot is in service with Germany, Israel, Japan, Kuwait, the Netherlands, Saudi Arabia and Taiwan. It has been ordered by Greece and has been cleared for sale to Egypt.

The Patriot missile is equipped with a track-via-missile (TVM) guidance system. Midcourse correction commands are transmitted to the guidance system from the mobile Engagement Control Centre. The target acquisition system in the missile acquires the target in the terminal phase of flight and transmits the data using the TVM downlink via the ground radar to the Engagement Control Station for final course correction calculations. The course correction commands are transmitted to the missile via the Missile Track Command Uplink. The high explosive 90 kg warhead is situated behind the terminal guidance section.

The range of the missile is 70 km and maximum altitude is greater than 24 km. The minimum flight time is the time to arm the missile, which is less than nine seconds, and the maximum flight time is less than three and a half minutes.

A new Patriot Advanced Capability (PAC-3) missile has increased effectiveness against tactical ballistic and cruise missiles, through the use of advanced hit-to-kill technology. Lockheed Martin is the prime contractor with Raytheon the systems integrator. The PAC-3 has a Ka-band millimetre wave seeker developed by Boeing. The missile guidance system enables target destruction through the kinetic energy released by hitting the target head-on.

In January 2000, Lockheed Martin received a contract for the low rate initial production of 20 PAC-3 systems. In July 2000, the PAC-3 missile successfully destroyed a cruise missile target during trials. The US Army is planning to field the first PAC-3 systems by the end of 2002. The Netherlands and South Korea have requested sales of PAC-3 missiles and Lockheed Martin and EADS (formerly DaimlerChrysler Aerospace) have established a joint venture company for the production of the system for the German Air Force.

A further development, designed to counter threats from cruise missiles, is the Patriot Anti Cruise Missile (PACM), which is a PAC-2 missile with a dual mode seeker, adding an active radar seeker to the existing TVM guidance. Raytheon conducted the first flight and intercept test of the missile in July 1999.

The M901 Launching Station transports, points and launches the Patriot missile. Each launcher has four missiles. The launcher is remotely operated via a VHF or fibre optic data link from the Engagement Control Station, which provides both the missile prelaunch data and the fire command signal.

The AN/MSQ-104 Engagement Control Station is the only manned station in a Patriot Fire Unit. The Control Station communicates with the M901 Launching Stations, with other Patriot batteries and the higher command headquarters.

The Control Station is manned by three operators, who have two consoles and a communications station with three radio relay terminals. The digital Weapon Control Computer is located next to the VHF Data Link Terminals.

The AN//MPQ-53 phased array radar carries out search, target detection, track and identification, missile tracking and guidance and electronic counter-countermeasures (ECCM) functions. The radar is mounted on a trailer and is automatically controlled by the digital weapons control computer in the Engagement Control Station, via a cable link. The radar system has a range of up to 100 km, capacity to track up to 100 targets and can provide missile guidance data for up to nine missiles.

A target engagement can be carried out in manual, semi-automatic or automatic mode. When the decision has been made to engage the target, the Engagement Control Station selects the Launch Station or Stations and pre-launch data is transmitted to the selected missile. After launch, the Patriot missile is acquired by the radar. The command uplink and the TVM downlink allow the missile's flight to be monitored and provide missile guidance commands from the weapon control computer. As the missile approaches the target, the TVM guidance system is activated and the missile is steered toward the target. A proximity fuse detonates the high explosive warhead.