MIM-104 Patriot

The MIM-104 Patriot is the primary surface-to-air missile (SAM) system used by the United States Army and several allied nations. It is manufactured by the Raytheon Company of the United States. The Patriot System replaced the Nike Hercules System as the U.S. Army's primary high/medium air defense platform, and replaced the HAWK System as the U.S. Army's medium tactical air defense platform. In addition to these roles, Patriot has assumed the role as the U.S. Army's anti-ballistic missile (ABM) platform, which today is Patriot's primary mission.

Patriot uses an advanced aerial interceptor missile and one of the world's highest performance radar systems (in terms of track quality). Patriot is the only ABM system to have successfully engaged and destroyed a tactical ballistic missile (TBM) in combat and the only SAM system which has successfully provided a maneuver force with tactical ballistic missile protection.

Patriot was developed at the Redstone Arsenal in Huntsville, Alabama, which had previously developed the Safeguard ABM system and its component Spartan and Sprint missiles.

The name "Patriot" can also be referred to as a backronym, taken from the phrase Phased Array TRacking to Intercept Of Target. The symbol for Patriot is a drawing of a Revolutionary War-era Minuteman.

Patriot systems have been sold to Greece, Israel, Germany, the Netherlands, Belgium, Japan and Spain.

Introduction

The MIM-104 Patriot was conceived in the late 1960s as a system combining several new technologies, including the phased array radar and track-via-missile guidance. Full-scale development of the system began in 1976 and it was deployed in 1984. Patriot was used initially as an anti-aircraft system, but in 1988 it was upgraded to provide limited capability against tactical ballistic missiles as PAC-1 (Patriot Advanced Capability-1). The most recent upgrade, called PAC-3, is a nearly total system redesign, intended from the outset to engage and destroy tactical ballistic missiles.

Patriot Equipment

The Patriot system has four major operational functions: communications, command and control, radar surveillance, and missile guidance. The four functions combine to provide a coordinated, secure, integrated, mobile air defense system.

The Patriot system is modular and highly mobile, as all components are truck or trailer mounted. The heart of the Patriot battery is the fire control section and associated launchers, consisting of the AN/MPQ-53 or -65 Radar Set, the AN/MSQ-104 Engagement Control Station (usually referred to as the "ECS" or more commonly as "the van"), the OE-349 Antenna Mast Group, and the EPP-III Electric Power Plant. The system's missiles are transported on and fired from the M901 Launching Station, which can carry up to four PAC-2 missiles or up to sixteen PAC-3 missiles. A Patriot battalion is also equipped with the Information Coordination Central, or ICC, a modified ECS which is designed to coordinate the fires of a battalion and uplink Patriot on to the JTIDS network.

The AN/MPQ-53 and AN/MPQ-65 Radar Set

The AN/MPQ-53/65 Radar Set is mounted on an M860 Semi-Trailer which is towed by an M983 HEMTT. It is a phased array radar which is equipped with IFF, electronic counter-countermeasure (ECCM) and track-via-missile (TVM) guidance subsystems. The Patriot Radar operates in the NATO G band frequency range, between 4 and 6 GHz.

The AN/MPQ-53 Radar Set equips PAC-2 and older units, and the AN/MPQ-65 Radar Set equips PAC-3 units. The main difference between these two radars is the addition of a second traveling wave tube (TWT), which gives the -65 radar increased search, detection, and tracking capability. The radar's antenna array consists of over 5,000 elements which "flash" the radar's beam many times per second. Additionally, the radar's antenna array contains an IFF interrogator subsystem, a track-via-missile array, and at least one "sidelobe canceller" (SLC), a small array designed to decrease interference that might affect the radar. Patriot's radar is somewhat unique in that it is a "detection-to-kill" system, meaning that a single unit performs all search, identification, track, and engagement functions. This is in contrast to most SAM systems, where several different radars are necessary to perform all functions necessary to detect and engage targets. The detection range of the Patriot radar is in excess of 100 km, and it can simultaneously track up to 100 targets.

The beam created by the Patriot radar is comparatively very narrow and highly agile, which gives the radar its unmatched ability to detect small, fast targets like ballistic missiles, or low radar cross section targets such as stealth aircraft or cruise missiles. Additionally, the power and agility of Patriot's radar is highly resistant to countermeasures, including electronic countermeasures (ECM) radar jamming and radar warning receiver (RWR) equipment. Patriot is capable of quickly jumping between frequencies to resist jamming.

The Patriot Radar costs in excess of $40 million.

The AN/MSQ-104 Engagement Control Station

The AN/MSQ-104 Engagement Control Station (ECS) is the nerve center of the Patriot firing battery. The ECS consists of a shelter which is mounted on the bed of an M927 5-Ton Cargo Truck or on the bed of a Light/Medium Tactical Vehicle (LMTV) Cargo Truck. The main sub-components of the ECS are the Weapons Control Computer (WCC), the Data Link Terminal (DLT), the UHF communications array, the Routing Logic Radio Interface Unit (RLRIU) and the two "manstations" that is the system's man-machine interface. The ECS is air conditioned, pressurized (to resist chemical/biological attack), and shielded against EMP burst or other such electromagnetic interference. The ECS also contains several SINCGARS radios to facilitate voice communications.

The WCC is the main computer within the Patriot system. It is a 24-bit parallel militarized computer with fixed and floating point capability. It is organized in a multiprocessor configuration which operates at a maximum clock rate of 6 megahertz. This computer runs the operator interface, calculates missile intercept algorithms, and provides limited fault diagnostics. Compared to modern personal computers it has somewhat limited processing power, although it has been upgraded several times during Patriot's service life.

The DLT (Data Link Terminal) is the system which connects the ECS to Patriot's Launching Stations. It uses either a SINCGARS radio or fiber optic cables to transmit encrypted data between the ECS and the launchers. Through the DLT, the system operators can remotely emplace, slew or stow launchers, perform diagnostics on launchers or missiles, and fire missiles.

The UHF communications array consists of three UHF radio "stacks" and their associated patching and encrypting equipment. These radios are connected to the antennas of the OE-349 Antenna Mast Group, which are used to create UHF "shots" between sister Patriot batteries and their associated ICC. This creates a secure, real-time data network (known as PADIL, Patriot Data Information Link) which allows for the ICC to centralize control of its subordinate firing batteries.

The Routing Logic Radio Interface Unit (RLRIU) functions as the primary router for all data coming into the ECS. The RLRIU gives a firing battery an address on the battalion data network, and sends/receives data from across the battalion. It also "translates" data coming from the WCC to the DLT, facilitating communication with the launchers.

Patriot's Manstations are referred to as Manstation 1 and 3 (MS1 and MS3). These are the stations where Patriot operators interface with the system. The manstations consist of a monochrome (green and black) screen surrounded by various Switch Indicators. Each Manstation also has a traditional QWERTY keyboard and "isometric stick", a tiny joystick that functions much like the mouse of a PC. It is through these switch indicators and the Patriot user interface software (organized into dozens of separate pages known as "tabs") that the system is operated.

The ECS costs in excess of $5 million.

The OE-349 Antenna Mast Group

The OE-349 Antenna Mast Group (AMG) is mounted on an M927 5-Ton Cargo Truck. It includes four 4 kW antennas in two pairs on remotely controlled masts. The antennas can be controlled in azimuth, and the masts can be elevated up to 100 feet 11 inches above ground level. Mounted at the base of each pair of antennas are two high-power amplifiers associated with the antennas and the radios in the collocated shelter. It is through these antennas that the ECS and ICC send their respective UHF "shots" in order to create the PADIL network.

The EPP-III Electric Power Plant

The EPP-III Electric Power Plant is the prime power source for the ECS and Radar which, together with EPP and AMG, comprise a Patriot fire control section. The EPP consists of two 150-kilowatt, 400-hertz diesel engines which are interconnected through the power distribution unit. These generators are mounted on an M983 HEMTT. Each EPP contains two interconnected 283.9-liter (75-gallon) fuel tanks, and a fuel distribution assembly with grounding equipment. Each diesel engine can operate more than eight hours with a full fuel tank. The EPP delivers its power to the Radar and ECS through massive cables stored in reels alongside the generators.

The M901 Launching Station

The M901 Launching Stations are remotely-operated, fully self-contained units. The ECS controls operation of the launchers through each launcher's DLT, via fiber optic or VHF (SINCGARS) data link. The LS is mounted on an M860 semitrailer towed by an M983 HEMTT, as is the Radar Set.

Integral leveling equipment permits emplacement on slopes of up to 10 degrees. Each launcher is trainable in azimuth and elevates to a fixed, elevated, launch position. Precise aiming of the launcher before launch is not necessary, thus no extra lags are introduced into system reaction time. Each Launcher is also capable of providing detailed diagnostics to the ECS via the data link.

The LS contains four major equipment subsystems: The launcher generator set, the launcher electronics module (LEM), the launcher mechanics assembly (LMA), and the launcher interconnection group (LIG). The generator set consists of a 15 kW, 400 Hz generator which powers the launcher. The LEM is used for the real-time implementation of launcher operations requested via data link from the ECS. The LMA physically erects and rotates the launcher's platform and its missiles. The LIG connects the missiles themselves to the launcher via the LMRD, or Launcher Missile Round Distributor.

The Patriot Guided Missile

There are a total of eight different variants of Patriot missiles: Standard, ASOJ/SOJC, PAC-2, PAC-2 GEM, GEM/C, GEM/T (or GEM+), and PAC-3.

The first fielded variant was the round MIM-104A, "Standard". It was optimized solely for engagements against aircraft and had very limited capability against ballistic missiles. The MIM-104B "ASOJ" or "anti standoff jammer" is a missile designed to seek out and destroy ECM emitters. The MIM-104C PAC-2 missile was the first Patriot missile which was optimized for ballistic missile engagements. The GEM series of missiles (MIM-104D/E) are further refinements of the PAC-2 missile. The PAC-3 missile is a totally new interceptor, featuring a Ka band active radar seeker and several other enhancements which dramatically increase its lethality against ballistic missiles. The specific information for these different kinds of missiles are discussed in the "Upgrades" section.

The first seven of these are in the larger PAC-2 configuration of a single missile per can, four of which can be placed on a launcher. PAC-3 missile canisters contain four missiles, and as such sixteen rounds in total can be placed on a launcher. All Patriot missiles consist of a missile (or missiles) mounted within a canister that is both the shipping and storage container and the launch tube. Patriot missiles are referred to as "certified rounds" as they leave the factory, and no additional maintenance is necessary on the missile prior to its being fired.

The PAC-2 missile is 5.31 meters long, weighs 900 kg and is propelled by a solid-fueled rocket motor at speeds in excess of Mach 5.

The Patriot missiles cost between $1 and $3 million dollars per copy, depending on variant.

Patriot Missile Design

The PAC-2 family of missiles all have a fairly standard design, the only differences between the variants being certain internal components. They consist of, from front to rear, the radome, guidance section, warhead section, propulsion section, and control actuator section.

The radome is made of slip cast fused silica approximately 16.5 millimeters (0.64 inch) thick, with nickel alloy tip, and a composite base attachment ring bonded to the slip cast fused silica and protected by a molded silicone rubber ring. The radome provides an aerodynamic shape for the missile and microwave window and thermal protection for the RF seeker and electronic components.

The Patriot guidance section consists primarily of the modular digital airborne guidance system (MDAGS). The MDAGS consists of a modular midcourse package which performs all of the required guidance functions from launch through midcourse and a terminal guidance section. The track-via-missile seeker is mounted on the guidance section, extending into the radome. The seeker consists of an antenna mounted on an inertial platform, antenna control electronics, a receiver, and a transmitter. The Modular Midcourse Package (MMP), which is located in the forward portion of the warhead section, consists of the navigational electronics and a missile borne computer which computes the guidance and autopilot algorithms and provides steering commands according to a resident computer program.

The warhead section, just aft of the guidance section, contains the proximity fused warhead, safety-and-arming device, fuzing circuits and antennas, link antenna switching circuits, auxiliary electronics, inertial sensor assembly, and signal data converter.

The propulsion section consists of the rocket motor, external heat shield, and two external conduits. The rocket motor includes the case, nozzle assembly, propellant, liner and insulation, pyrogen igniter, and propulsion arming and firing unit. The casing of the motor is an integral structural element of the missile airframe. It contains a conventional, casebonded solid rocket propellant.

The Control Actuator Section (CAS) is at the aft end of the missile. It receives commands from the missile autopilot and positions the fins. The missile fins steer and stabilize the missile in flight. A fin servo system positions the fins. The fin servo system consists of hydraulic actuators and valves and an electrohydraulic power supply. The electrohydraulic power consists of battery, motor pump, oil reservoir, gas pressure bottle, and accumulator.

Patriot Upgrades

The modular nature of the Patriot system has made both hardware and software upgrades a relatively simple and continuous process throughout the system's service. The most common upgrades have been to the software and to the missiles themselves, though just about every major sub-component of the system has seen at least one upgrade at one point.

Patriot was first introduced with a single missile type: the MIM-104A. This was the initial "Standard" missile (still known as "Standard" today). In these early days the system was used exclusively as an anti-aircraft weapon, and this initial variant had no capability against ballistic missiles. This was remedied in the late 1980s, when Patriot received its first major system overhaul with the introduction of the Patriot Advanced Capability missile and concurrent system upgrades.

Patriot Advanced Capability (PAC)

Patriot Advanced Capability, known today as the PAC-1 upgrade, was a software-only upgrade. The most significant aspects of this upgrade was changing the way the radar searched and the way the system defended its assets. Instead of searching low to the horizon, the top of the radar's search angle was lifted to near vertical (89 degrees) from the previous angle of 25. This was done as a counter to the steep parabolic trajectory of inbound ballistic missiles. The search beams of the radar were tightened, and while in "TBM search mode" the "flash", or the speed at which these beams were shot out, was increased significantly. While this increased the radar's detection capability against the ballistic missile threat set, it decreased the system's effectiveness against traditional atmospheric targets, as it reduced the detection range of the radar as well as the number of "flashes" at the horizon. Because of this, it was necessary to retain the search functions for traditional atmospheric threats in a separate search program, which could be easily toggled by the operator based on the expected threat. Additionally, the ballistic missile defense capability changed the way Patriot defended targets. Instead of being used as a system to defend a significant area against enemy air attack, it was now used to defend much smaller "point" targets, which needed to lie within the system's TBM "footprint". The footprint is the area on the ground that Patriot can defend against inbound ballistic missiles.

Through the 1980s, Patriot saw a number of smaller upgrades, mostly to its software. Most significant of these was a special upgrade to discriminate and intercept artillery rockets in the vein of the Multiple Launch Rocket System, which was seen as a significant threat to South Korea. This feature has not been used in combat and has since been deleted from US Army Patriot systems, though it remains in South Korean systems. Another upgrade the system saw was the introduction of another missile type, designated MIM-104B and called "ASOJ" or "anti stand-off jammer" by the Army. This variant is designed to help Patriot engage and destroy ECM aircraft at standoff ranges. It works similar to an anti-radiation missile in that it flies a highly lofted trajectory and then locates, homes in on, and destroys the most significant emitter in an area designated by the operator.

PAC-2

In the late 1980s, tests began to indicate that, although Patriot was certainly capable of intercepting inbound ballistic missiles, it was questionable whether or not the MIM-104A/B missile was capable of reliably destroying them. This necessitated the introduction of the PAC-2 missile and system upgrade.

For the system, the PAC-2 upgrade was similar to the PAC-1 upgrade. Radar search algorithms were further optimized, and the beam protocol while in "TBM search" was further modified. PAC-2 also saw Patriot's first major missile upgrade, with the introduction of the MIM-104C, or PAC-2 missile. This missile was optimized for ballistic missile engagements. Major changes to the PAC-2 missile were the size of the projectiles in its blast-fragmentation warhead (changed from around 2 grams to around 45 grams), and the timing of the pulse-doppler fuse, which was optimized for high-speed engagements (though it retained its old algorithm for aircraft engagements if necessary). Engagement procedures were also optimized, changing the method of fire the system used to engage ballistic missiles. Instead of firing two missiles in an almost simultaneous salvo, a brief delay (between 3 and 4 second) was added in order to allow the second missile fired to discriminate a ballistic missile warhead in the aftermath of the explosion of the first.

PAC-2 was first tested in 1987 and reached Army units in 1990, just in time for deployment to the middle east for the Persian Gulf War. It was here that Patriot became the first successful ABM system, and though its actual performance numbers remain classified (and controversial despite it) it proved that ballistic missile defense was indeed possible.

There have been many more upgrades to PAC-2 systems throughout the 1990s and into the 21st century, again mostly centering on software. However, the PAC-2 missiles have been modified significantly, into four separate variants known collectively as "GEM" or "guidance enhanced" missiles.

The chief upgrade to the original GEM missile was a new, much faster proximity fused warhead. Tests had indicated that the fuse on the original PAC-2 missiles were detonating their warheads too late when engaging ballistic missiles with an extremely steep ingress, and as such it was necessary to shorten this fuse delay. The GEM missile was also given a new "low noise" seeker head designed to reduce interference in front of the missiles radar seeker, and a higher performance seeker designed to better detect low radar cross section targets, such as stealth aircraft. The GEM was used extensively in Operation Iraqi Freedom, with a perfect success rate.

Just prior to OIF, it was decided to further upgrade the GEM and PAC-2 missiles. This upgrade program produced missiles known as the GEM/T and the GEM/C, the "T" designator referring to "TBM", and the "C" designator referring to cruise missiles. These missiles were both given a totally new nose section, which was designed specifically to be more effective against low altitude, low RCS targets like cruise missiles. Additionally, the GEM/T was given a new fuse which was further optimized against ballistic missiles. The GEM/C is the upgraded version of the GEM, and the GEM/T is the upgraded version of the PAC-2. The GEM+ entered service in 2002, and the Army is currently having all of its PAC-2 and GEM missiles upgraded to the GEM/C or GEM/T standard.

PAC-3

The PAC-3 upgrade is the most significant upgrade Patriot has received thus far, and is one of the most comprehensive upgrade programs ever undertaken on an American weapon system. Nearly every aspect of the system received a significant upgrade. The PAC-3 upgrade took place in three stages, and units were designated Configuration 1, 2, or 3 based on the stage of upgrade they were in.

The system itself saw another upgrade of its WCC and its software, and the communication setup was given a complete overhaul. Thanks to this upgrade, PAC-3 operators can now see tracks on the JTIDS, or Joint Tactical Information Distribution System network, which greatly increases the situational awareness of Patriot crews. The software can now conduct a "tailored TBM search", optimizing radar resources for search in a particular sector known to have ballistic missile activity, and can also support a "keepout altitude" to ensure ballistic missiles with chemical warheads or ERS ("early release submunitions") are destroyed at a certain altitude. For Configuration 3 units, the Patriot Radar was completely redesigned, adding an additional TWT (traveling wave tube) which increased the radar's search, detection, tracking, and discrimination abilities to previously unheard of levels. In fact, the PAC-3 radar is capable, among other things, of detecting whether or not an aircraft is manned and whether or not it is carrying ordnance.

The PAC-3 upgrade carried with it a new missile design, nominally known as MIM-104F and called PAC-3 by the Army. The PAC-3 missile is the most advanced aerial interceptor ever developed, dedicated almost entirely to the anti-ballistic missile mission. Miniaturization has made the PAC-3 missile much smaller than the previous Patriot missiles; a single "can" can now hold four missiles where one was once held. The PAC-3 missile is also much more maneuverable than previous variants, thanks to dozens of tiny rocket motors mounted in the forebody of the missile (called ACMs, or Attitude Control Motors). However, the most significant upgrade to the PAC-3 missile is the addition of a Ka band active radar seeker. This allows the missile to drop its uplink to the system and acquire its target itself in the terminal phase of its intercept, which improves the reaction time of the missile against a fast-moving ballistic missile target; the PAC-3 missile is, in fact, accurate enough to select, target, and home in on the warhead portion of an inbound ballistic missile. The active radar also increases the missile's ability to discriminate debris and decoys that may be around the warhead, and gives the warhead a "hit-to-kill" capability that completely removes the need for a traditional proximity-fused warhead. This greatly increases the lethality against ballistic missiles of all types.

All told, the PAC-3 upgrade has effectively quintupled the "footprint" that a Patriot unit can defend against ballistic missiles of all types, and has considerably increased the system's lethality and effectiveness against ballistic missiles. It has also increased the scope of ballistic missiles that Patriot can engage, which now includes several intermediate range and continental ballistic missiles such as the Nodong and the CSS-2 and CSS-3. However, despite its increases in ballistic missile defence capabilities, the PAC-3 missile is a less capable interceptor of atmospheric aircraft and air-to-surface missiles. It is slower, has a shorter range, and has a smaller explosive warhead compared to older Patriot missiles (although it generally relies on its kinetic "hit to kill" warhead).

Patriot's PAC-3 interceptor will be the primary interceptor for the new MEADS system, which is scheduled to enter service alongside Patriot in 2012.

The Future

Patriot upgrades continue, with the most recent being new software known as PDB-6 (PDB standing for "Post Deployment Build"). This software will allow configuration 3 units to discriminate targets of all types, to include anti-radiation missile carriers, helicopters, unmanned aerial vehicles, and cruise missiles.

The PAC-3 missile is currently undergoing testing for a significant new upgrade, currently referred to as "MSE" or "Missile Section Enhancement". The upgrade is similar to the GEM+T/C upgrade, in that it consists of a body redesign and subsequent replacement of the PAC-3 interceptor. The upgrade includes a new fin design and a new, more powerful rocket motor. The modification is alleged to increase the operational capability of the current PAC-3 missile up to 50% and is scheduled to be added to all existing PAC-3 missile stores by 2008.

Further upgrades to the dual-TWT radar set, the JTIDS uplink, and the system's processors and memory are scheduled to take place in the next few years.

The Patriot Battalion

In the US Army, The Patriot System is designed around the battalion echelon. A Patriot Battalion consists of a headquarters battery (which includes the Patriot ICC and its operators), a maintenance company, and between four and six "line batteries", which are the actual firing batteries that employ the Patriot systems. Each line battery consists three platoons: Fire Control platoon, Launcher platoon, and Headquarters/Maintenance platoon. The Fire Control platoon is responsible for operating and maintaining the "big 4". Launcher platoon operates and maintains the launchers, and Headquarters/Maintenance platoon provides the battery with maintenance support and a headquarters section. The Patriot line battery is commanded by a captain and usually consists of between 70 and 90 soldiers. The Patriot battalion is commanded by a lieutenant colonel and can include as many as 600 soldiers.

Once emplaced, the system requires a crew of only three individuals to operate. The Tactical Control Officer (TCO), usually a lieutenant, is responsible for the operation of the system. The TCO is assisted by the Tactical Control Assistant (TCA). Communications are handled by the third crewmember, the communications system specialist. The ICC crew is similar, except its operators are designated as the Tactical Director (TD) and the Tactical Director Assistant (TDA).

Patriot battalions prefer to operate in a centralized fashion, with the ICC controlling the fires of all of its subordinate firing batteries through the secure UHF PADIL communications network.

The US Army operates ten Patriot battalions: 1-1 ADA and 3-2 ADA of the 31st ADA Brigade (assigned to III Armored Corps), 1-7 ADA and 2-43 ADA of the 108th ADA Brigade (assigned to XVIII Airborne Corps), 5-7 ADA and 6-52 ADA of the 69th ADA Brigade (assigned to V Armored Corps, Germany), 1-43 ADA and 2-1 ADA assigned to the 35th ADA Brigade (Korea), and 3-43 ADA and 5-52 ADA of the 11th ADA Brigade (assigned to the 32nd AAMDC).

Operation

Following is the process a PAC-2 firing battery uses to engage a single target (an aircraft) with a single missile:

A hostile aircraft is detected by the AN/MPQ-53 Radar. The radar examines the track's size, speed, altitude, and heading, and decides whether or not it is a legitimate track or "clutter" created by RF interference.
If the track is classified by the radar as an aircraft, in the AN/MSQ-104 Engagement Control Station, an unidentified track appears on the screen of the Patriot operators. The operators examine the speed, altitude and heading of the track. Additionally, the IFF subsystem "pings" the track to determine if it has any IFF response.
Based on many factors, including the track's speed, altitude, heading, IFF response, or its presence in "safe passage corridors" or "missile engagement zones", the ECS operator, the TCO (tactical control officer), makes an ID recommendation to the ICC operator, the TD (tactical director).
The TD examines the track and decides to certify that it is hostile. Typically, the engagement authority for Patriot units rests with the Regional or Sector Air Defense Commander (RADC/SADC), who will be located either on a US Navy guided missile cruiser or on a USAF AWACS aircraft. A Patriot operator (called the "ADAFCO" or Air Defense Artillery Fire Control Officer) is colocated with the RADC/SADC to facilitate communication to the Patriot battalions.
The TD contacts the ADAFCO and correlates the track, ensuring that it is not a friendly aircraft.
The ADAFCO obtains the engagement command from RADC/SADC, and delegates the engagement back down to the Patriot battalion.
Once the engagement command is received, the TD selets a firing battery to take the shot and orders them to engage.
The TCO instructs the TCA to engage the track. The TCA brings the system's launchers from "standby" into "operate".
The TCA presses the "engage" switch indicator. This sends a signal to the selected launcher and fires a missile selected automatically by the system.
The AN/MPQ-53 Radar, which has been continuously tracking the hostile aircraft, "acquires" the just-fired missile and begins feeding it interception data. The Radar also "illuminates" the target for the missile's semi-active radar seeker.
The monopulse receiver in the missile's nose receives the reflection of illumination energy from the target. The track via missile uplink sends this data through an antenna in the missile's tail back to the AN/MPQ-53 set. In the ECS, computers calculate the maneuvers that the missile should perform in order to maintain a trajectory to the target and the TVM uplink sends these to the missile.
Once in the vicinty of the target, the missile detonates its proximity fused warhead.

Following is the process a PAC-3 firing battery uses to engage a single tactical ballistic missile with two PAC-3 missiles:

A missile is detected by the AN/MPQ-65 radar. The radar reviews the speed, altitude, behavior, and radar cross section of the target. If this data lines up with the discrimination parameters set into the system, the missile is presented on the screen of the operator as a ballistic missile target.
In the AN/MSQ-104 Engagement Control Station, the TCO reviews the speed, altitude, and trajectory of the track and then authorizes engagement. Upon authorizing engagement, the TCO instructs his TCA to bring the system's launchers into "operate" mode from "standby" mode. The engagement will take place automatically at the moment the computer determines will provide the highest probability of kill.
The system computer determines which of the battery's launchers have the highest probability of kill and selects them to fire. Two missiles are launched 4.2 seconds apart in a "ripple".
The AN/MPQ-65 radar continues tracking the target and uploads intercept information to the PAC-3 missiles which are now outbound to intercept.
Upon reaching its terminal homing phase, the Ka band active radar seeker in the nose of the PAC-3 missile acquires the inbound ballistic missile. This radar selects the radar return most likely to be the warhead of the incoming missile and directs the interceptor towards it.
The ACMs (attitude control motors) of the PAC-3 missile fire to precisely align the missile on the interception trajectory.
The interceptor flies straight through the warhead of the inbound ballistic missile, detonating it and destroying the missile.
The second missile locates any debris which may be a warhead and attacks in a similar manner.

Patriot in the Persian Gulf War (1991)

Trial by fire

Prior to the Persian Gulf War, ballistic missile defense was an unproven concept in war. During Operation Desert Storm, in addition to its anti-aircraft mission, Patriot was assigned to shoot down incoming Iraqi Scud or Al Hussein short range ballistic missiles launched at Israel and Saudi Arabia. The first combat use of Patriot occurred 18 January 1991 when it successfully intercepted and destroyed an Iraqi Scud missile fired at Saudi Arabia. This was the first time an air defense system destroyed a hostile theatre ballistic missile (TBM) in combat.

Throughout the war, Patriot attempted engagement of over 40 hostile ballistic missiles. The success of these engagements is still controversial to this day.

Failure at Dharan

On February 25, 1991, an Iraqi Scud hit the barracks in Dharan, Saudi Arabia, killing 28 soldiers from the US Army's 14th Quartermaster Detachment.

A government investigation revealed that the failed intercept at Dharan had been caused by a software error in the system's clock. The Patriot missile battery at Dharan had been in operation for 100 hours, by which time the system's internal clock had drifted by one third of a second. For a target moving as fast as an inbound TBM, this was equivalent to a position error of 600 meters.

The radar system had successfully detected the Scud and predicted where to look for it next, but because of the time error, looked in the wrong part of the sky and found no missile. With no missile, the initial detection was assumed to be a spurious track and the missile was removed from the system. No interception was attempted, and the missile impacted on a barracks killing 28 soldiers.

At the time, the Israelis had already identified the problem and informed the US Army and the PATRIOT Project Office (the software manufacturer) on February 11, 1991, but no upgrade was present at the time. As a stopgap measure, the Israelis recommended rebooting the system's computers regularly, however, Army officials did not understand how often they needed to do so. The manufacturer supplied updated software to the Army on February 26, the day after the Scud struck the Army barracks.

Success rate vs. accuracy

The U.S. Army claimed an initial success rate of 80% in Saudi Arabia and 50% in Israel. Those claims were eventually scaled back to 70% and 40%. However, when President George H. W. Bush traveled to Raytheon's Patriot manufacturing plant in Andover, Massachusetts during the Gulf War, he declared, the "Patriot is 41 for 42: 42 Scuds engaged, 41 intercepted!" ^*. The President's claimed success rate was thus over 97% during the war.

On April 7, 1992 Theodore Postol of the Massachusetts Institute of Technology, and Reuven Pedatzur of Tel Aviv University testified before a House Committee stating that, according to their independent analyses, the Patriot system had a success rate of below 10%, and perhaps even a zero success rate. In response to this testimony and other evidence, the staff of the House Government Operations Subcommittee on Legislation and National Security reported, "The Patriot missile system was not the spectacular success in the Persian Gulf War that the American public was led to believe. There is little evidence to prove that the Patriot hit more than a few Scud missiles launched by Iraq during the Gulf War, and there are some doubts about even these engagements. The public and the Congress were misled by definitive statements of success issued by administration and Raytheon representatives during and after the war." ^*

Also on April 7, 1992 Charles A. Zraket of the Kennedy School of Government, Harvard University and Peter D. Zimmerman of the Center for Strategic and International Studies testified about the calculation of success rates and accuracy in Israel and Saudi Arabia and discounted many of the statements and methodologies in Postol's report.

Success Rate – the percentage of Scuds destroyed or deflected to non-populated areas
Accuracy – the percentage of hits out of all the Patriots fired

It is important to note the difference in terms when analyzing the performance of the system during the war.

According to Zimmerman, in accordance with the standard firing doctrine on average four Patriots were launched at each incoming Scud – in Saudi an average of three Patriots were fired. If every Scud were deflected or destroyed the success rate would be 100% but the Accuracy would only be 25% and 33% respectively.

Both testimonies state that part of the problems stem from its original design as an anti-aircraft system. PATRIOT was designed with proximity fuzed warheads, which are designed to explode immediately prior to hitting a target spraying shrapnel out in a fan in front of the missile, either destroying or disabling the target. These missiles were fired at the target's center of mass. With aircraft this was fine, but considering the much higher speeds of TBMs, as well as the location of the warhead (usually in the nose), PATRIOT would most often hit closer to the tail of the Scud due to the delay present in the proximity fuzed warhead, thus not destroying the TBM's warhead and allowing it to fall to earth.

The Iraqi redesign of the Scuds also played a role. Iraq had redesigned its Soviet-style Scuds to be faster and longer ranged, but the changes weakened the missile and it was more likely to break up upon re-entering the atmosphere. This presented a larger number of targets as it was unclear which piece contained the warhead.

What all these factors mean, according to Zimmerman, is that the calculation of "Kills" becomes more difficult. Is a kill the hitting of a warhead or the hitting of a missile? If the warhead falls into the desert because a PATRIOT hit its Scud, is it a success? What if it hits a populated suburb? What if all four of the engaging PATRIOT missiles hit, but the warhead falls anyway because the Scud broke up?

According to the Zraket testimony there was a lack of high quality photographic equipment necessary to record the interceptions of targets. Therefore, PATRIOT crews recorded each launch on videotape, and damage assessment teams recorded the Scud debris that was found on the ground. Crater analysis was then used to determine if the warhead was destroyed before the debris crashed or not. Furthermore, part of the reason for the 30% improvement in success rate in Saudi Arabia compared to Israel is that the PATRIOT merely had to push the incoming Scud missiles away from military targets in the desert or disable the Scud's warhead in order to avoid casualties, while in Israel the Scuds were aimed directly at cities and civilian populations. The Saudi Government also censored any reporting of Scud damage by the Saudi press. The Israeli Government did not institute the same type of censorship. Furthermore, PATRIOT's success rate in Israel was examined by the IDF (Israel Defense Forces) who did not have a political reason to play up PATRIOT's success rate. The IDF counted any Scud that exploded on the ground (regardless of whether or not it was diverted) as a failure for the Patriot. Meanwhile, the U.S. Army who had many reasons to support a high success rate for PATRIOT, examined the performance of PATRIOT in Saudi Arabia.

A Canadian Broadcasting Corporation documentary quotes the former Israeli Defense Minister as saying the Israeli government was so dissatisfied with the performance of the missile defense, that they were preparing their own military retaliation on Iraq regardless of US objections. That response was cancelled only with the cease fire with Iraq.

Psychological effects of the system

Saddam Hussein had vowed to rain down missiles on Israel with hopes of provoking Israel to attack, thus aligning Iraq with the Arab's common cause and possibly causing those who were members of the coalition to withdraw. If this occurred the United States and its allies would lose crucial support and in Hussein's mind would not be able to continue the war.

Israel was concerned over the use of biological or chemical agents in the Scuds. The Patriot gave the Israeli government a way to calm their people in the early days of the war.

In the Iraqi bombardments on Israel two people were killed and several hundred were injured. In contrast, seven Israelis suffocated while wearing gas masks out of fear that the Scuds would be laden with chemical agents.

Patriot in Operation Iraqi Freedom (2003)

Patriot was deployed to Iraq a second time in 2003, this time to provide air and missile defence for the forces conducting Operation Iraqi Freedom (OIF). Postwar reports described Patriot's deployment as a "tremendous success", although there were tragedies associated with its triumph.

Patriot batteries had at least eight independently confirmed TBM kills during the campaign, and Patriot batteries themselves reported successfully shooting down all eleven Iraqi TBMs that threatened coalition assets, including one TBM that would have struck the headquarters of the 101st Airborne Division and another that would have struck the Combined Land Forces Command Center, the highest echelon command location in Iraq at the time. Echo Battery, 2nd Battalion, 43rd Air Defense Artillery fired and successfully engaged with the first PAC-3 missiles in combat. Patriot also provided radar surveillance for coalition assets who lacked a clear picture over much of Iraq.

Patriot PAC-3, GEM, and GEM+ missiles both had a very high success rate intercepting Al Samoud-2 and Ababil-100 tactical ballistic missiles^*. However, no longer-range ballistic missiles were fired during that conflict. Additionally, Patriot, as well as all other coalition air defense assets, were defeated by a relatively primitive CSS-C-3 "Seersucker" anti-ship cruise missile, although this missile did no damage.

Operation Iraqi Freedom marked the first use of Patriot to maneuver with and cover the forward combat elements in a large operation - previously, it had been thought that the system was too large to be quickly redeployed, and its use was restricted to defending primarily stationary assets. However, during Operation Iraqi Freedom, several Patriot batteries successfully "leapfrogged" forward to protect the airspace above the units driving towards Baghdad in the first weeks of the war. However, the maneuvering of the Patriot batteries made establishing communications between Patriot units highly difficult, which contributed to at least one fratricide, mentioned below.

Patriot Fratricides (Friendly Fire)

Patriot had two fratricides in Iraq, one against a British RAF Tornado GR4A killing both crew, the other against an F/A-18 Hornet killing the pilot.

The Tornado was engaged because the system mistakenly classified it as an anti-radiation missile (ARM), which is a threat typically engaged automatically by the system. This fratricide was a result of mistakes on many different levels. First, the path the Tornado was flying in preparation for landing took it directly over the Patriot firing battery. Second, Patriot planners had made the parameters by which the system classifies ARMs too wide, which allowed for a track appearing like the Tornado to be classified as an ARM by the system. Third, Patriot planners had left the "ARM classification" protocol activated, despite the fact that Iraq had no ARMs. Fourth, the Patriot firing battery had no communications with any higher echelon unit. Fifth, and probably most significantly, the Tornado did not have its IFF transponder on, which could have been an instant indication of the misclassification.

The other fratricide, on an F/A-18 Hornet, was a Patriot system and operator error resulting from a misclassified TBM. The system engaged the Hornet automatically after the software, in conjunction with the Patriot radar, incorrectly classified the aircraft as a TBM inbound for the Karbala Gap region, where US Army ground forces were currently operating. The Tactical Control Officer and Tactical Director failed to check that the speed and altitude of the track were commensurate with that of a ballistic missile, and the aircraft was engaged with a PAC-3 missile shortly after firing battery's launching stations were ordered into operation. The aircraft that was flying with the F/A-18 Hornet was almost engaged by another firing battery, until the order was given to disregard.

A third Blue-on-blue incident occurred when the Radar Warning Receiver (RWR) of a USAF F-16 Falcon incorrectly identified a Patriot battery as an SA-2 battery. At the time, the Patriot battery was protecting the 101st Airborne Division's Headquarters near the Forward Line of Troops (FLOT). The F-16 fired an AGM-88 HARM missile, which struck directly in front of the Patriot Radar Set, putting it out of action. The affected Patriot unit was forced to swap its radar set with another unit's in the immediate area. This replacement radar set had not fully undergone a testing period after receiving its PAC-3 upgrade/enhancements, and later the same battery was responsible for the fratricide of the F/A-18 mentioned above.

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