The MIM-104 Patriot is the U.S. Army’s primary air and missile defense system. Initially designed as an antiaircraft system, Patriot gained attention in the 1991 Gulf War when it was used as an impromptu defense against Iraqi Scud missiles. Since then, Patriot and its related interceptors have been optimized for defense against tactical ballistic missiles, but remains capable against aerial threats such as aircraft and cruise missiles. Today, 13 countries operate Patriot. In addition to the launcher system displayed here, the Patriot system also includes radars, remote command and control units, and other support equipment.

Early Development

The idea for a mobile air defense system utilizing missile interceptors was first conceptualized in 1961 at the U.S. Army Missile Command and by 1965, the SAM-D development program had been established. The system was initially designed as an anti-aircraft, surface-to-air defense battery, but subsequent upgrades allow for defense against a wide array of air targets. Development test launches began five years later in 1970, with full-scale engineering development starting in 1976. The SAM-D program took the name Patriot during the U.S. Bicentennial in 1976.1 By 1985, the U.S. Army declared the Patriot fully operational.2


The Patriot missile defense system consists of 4 major components: the launcher, configured with four interceptors per launcher for the PAC-1/2 and 16 interceptors per launcher for the PAC-3; the AN/MPQ-53 phased-array radar, designed to track enemy missiles or aircraft; the AN/MSQ-104 Engagement Control Station (ECS), the “man in the loop” for firing an interceptor; and the AN/MSQ-24, the 150 kW diesel powered generator units.3

Patriot PAC-1

The Patriot Level-1 anti-tactical missile (ATM or Patriot Advanced Capability-1 [PAC-1]) primarily consisted of software changes allowing for the interceptors to be used to defend against short-range ballistic missiles (SRBMs) and it was deployed in Europe in 1988.4

Patriot PAC-2

Its successor, the PAC-2, consisted of further software upgrades and improvements to the blast fragmentation warhead. The PAC-2 was the first ballistic missile defense system to successfully intercept a hostile ballistic missile during wartime. During the 1991 Gulf War, the United States deployed PAC-2 interceptors to Israel and Saudi Arabia to counter the Iraqi arsenal of Scud missiles. The GAO concluded that there was evidence that nine percent of the engagements during the conflict could be conclusively considered “warhead kills,” where there was either evidence of Patriot fragments in the body of Scud missiles or radar evidence of debris from a destroyed Scud. However, the


lack of certain equipment and inconsistent ground tracking contributes to significant uncertainty about the effectiveness of Patriots during the Gulf War.5

After the Gulf War, the United States sought to upgrade the PAC-2 interceptors using lessons learned during these first engagements. The Army began development of the Guidance Enhanced Missile (GEM) with the goal of upgrading current interceptors while a PAC-3 interceptor could be developed. The major upgrades for the GEM series of interceptors include an improved seeker to illuminate low-radar cross section targets and an upgraded proximity fuse to improve performance against high-speed ballistic missiles. The GEM missile entered production in 1994.6 The Army produced a GEM-T variant that was designed to combat theater ballistic missiles and a GEM-C variant that was suited to defeating cruise missiles.7 The GEM+ interceptor replaced older components and provided further upgrades to the seeker and proximity fuses. It entered service in 2002.8

Patriot PAC-3

The PAC-3 interceptor differs significantly from the PAC-1/2 interceptors due to its use of hit-to-kill technology. While previous Patriot interceptors used only a blast fragmentation detonation in the vicinity of the hostile target, the PAC-3 hits the target directly and only contains a small high explosive warhead as a kill enhancer. The interceptor was a direct result of the Extended Range Interceptor (ERINT) program, which developed a hit-to-kill interceptor to compete with an upgraded PAC-2 called the MultiMode Seeker (MMS).9 In 1994, the Acquisition Review Council concluded the ERINT, which was smaller and allowed for greater range and accuracy, should be the new interceptor for the PAC-3 version of Patriot and merged the programs. The first PAC-3 interceptors were delivered in 2001 and the program was declared operationally ready in October 2002.10 Later, the United States developed a Cost Reduction Initiative version of the PAC-3 interceptor that included block upgrades to reduce unit prices.11

The PAC-3 configuration was used in combat during Operation Iraqi Freedom in 2003 and went two-for-two in engagements with the shorter range and slower Scud missiles fired by the Saddam Hussein regime. Seven more intercepts took place with the older PAC-2 interceptors, giving the system a nine-for-nine record on targeted missiles. It did not target six other Scuds because they were projected to land in non-threatening areas. Patriot units also engaged in three friendly fire incidents, including shooting down British and American aircraft.12

Two proposed upgrades to the original PAC-3 configuration include an extended-range enhancement to the ground-launched interceptor and an air-launched variant. The land-based interceptor upgrade, the Missile Segment Enhancement (MSE) program, includes a dual-pulse solid-rocket motor, larger control fins, and upgraded support systems that could effectively double the range of the missile.13 The U.S. Army received its first MSE interceptors in October 2015 and, in November and December 2015, the MSE missile had two successful intercept tests.14

The air-launched hit-to-kill (ALHTK) development program proposed using a PAC-3 interceptor launched from an Air Force platform. The idea was to integrate a proven defensive system with the mobility of an air-launched platform by expanding the range and potentially adding boost and midcourse phase intercept capabilities. Additionally, industry sources claim the PAC-3 interceptors could achieve up to six times the range of the land-based system due to the reduction in fuel use needed to obtain cruising speed.

After the Gulf War, the United States also pursued upgrades to the rest of the Patriot system, deciding to build the PAC-3 system in incremental configurations. The PAC-3 Configuration 1 was first fielded in 1995 and incorporated the GEM interceptor with upgrades for the engagement control station and an improved pulse-Doppler radar processor. The Configuration 2 included compatibility with Link 16, allowing greater integration with other missile tracking systems and more improvements to the radar and was introduced in 1996. The PAC-3 Configuration 3, which first deployed in 2003, was the first to actually deploy the PAC-3 interceptor and included radar upgrades that allow for better target discrimination.15

The AN/MSQ-104 ECS is essentially the brain of the Patriot system. It is the only manned portion of the Patriot batteries, consisting of three (or sometimes four) individuals. The Patriot system is nearly autonomous, with only the final launch decision requiring human interaction. The ECS has two computer consoles, each displaying a radar depiction of airborne vessels. The tactical control officer sits to the right; the tactical control assistant sits to the left; and the communications operator sits in the back. The tactical control assistant does the actual ‘firing’ of the interceptors; the tactical control officer approves targets and ensures that allied forces are not targeted; and the communications operator monitors all communication between headquarters and the other batteries. Sometimes a recorder assists the tactical control assistant and records messages from headquarters.16

The AN/MPQ-53 phased-array radar is a significant departure from the standard constant-beam radar. The phased-array radar emits a rapid and random radar beam, thousands of times per second, making it tougher for an enemy to jam the signal. After an interceptor is launched, it begins relaying flight data back to the radar allowing for more accurate terminal guidance.17 The PAC-3 final configuration also included an upgrade to the radar to the AN/MPQ-65, which adds detection capability in high clutter environments.18 A new Gallium Nitride-based Active Electronically Scanned Array radar is in development for the Patriot system to provide 360 degree coverage in comparison to the older radars’ 120 degree radar coverage. The new system uses three antenna arrays with one main array pointing in the anticipated threat direction and two smaller arrays looking to the back and sides of the main array.19

Fourteen countries possess or have purchased some version of the Patriot system including: Germany, Greece, Israel, Japan, Kuwait, the Netherlands, Poland, Qatar, Saudi Arabia, South Korea, Spain, Taiwan, UAE, and U.S. Patriot missiles are also deployed around the world to provide point defense in response to potential missile attacks. The United States deploys Patriot batteries in eight countries abroad including: Bahrain, Germany, Japan, Jordan, Kuwait, Qatar, South Korea, and the UAE.

In February 2013, NATO agreed to place six batteries near the Turkish-Syrian border to protect against ballistic missiles.20 In 2015, The United States and Germany withdrew their deployments of Patriot missiles from Turkey. However, Spain has agreed to keep its PAC-2 battery in Turkey until the end of 2016.21 Saudi and UAE Patriot units have also played an important role in Gulf Cooperation Council operations in Yemen. Saudi and UAE Patriot systems intercepted both Tochka and Scud missiles fired by Houthi rebels at targets in Saudi Arabia and Yemen.22