Update 11/6/2017: On November 4, 2017, a Patriot missile system intercepted a Burqan 2H ballistic missile destined for the King Khalid International Airport in the Saudi capital of Riyadh. This engagement, which likely prevented tens if not hundreds of casualties, further demonstrates Patriot’s ability to reliably defend critical infrastructure.

The Patriot is a surface-to-air missile (SAM) system fielded by a multitude of militaries, including the United States, Israel, the Netherlands, Japan, and Saudi Arabia. In service since the 1980s, Patriot is the primary air defense system for the US military, and over one thousand launchers have been built. An operational Patriot battery includes a missile launcher unit, a generator unit, an antennae mast group, a radar unit, and a number of other support components. The Patriot system is comparable to the S-300 missile system fielded by Russia and many other countries in that both are modern, road-mobile, radar-guided SAM systems.

The Patriot system has undergone many changes since its initial introduction in 1984. At the start, Patriot was designed solely for use against airbreathing targets, e.g. cruise missiles, helicopters, airplanes, etc. However, as the US Army’s primary high-performance air defense system, the Patriot was later tasked with ballistic missile defense as well. To add this capability, engineers programmed ballistic missile defense mode, which altered the behavior of the radar so that it would scan much higher — 89 degrees from the horizontal as opposed to 25. This alteration allowed the Patriot’s radar to detect ballistic missiles, which follow a parabolic flight path. The higher scanning profile resulted in a tradeoff: performance against traditional threats was diminished, so operators were instructed to switch between the airbreathing target detection and ballistic target detection modes based on the anticipated threat. This version of the Patriot with upgraded software, called the Patriot Advanced Capability-1 (PAC-1), was capable of engaging ballistic missiles, but it still had critical shortcomings.

Patriot PAC-2 was introduced to further enhance the Patriot system’s ballistic missile engagement capabilities and to rectify issues with PAC-1. While PAC-2 included further software changes, it also made much-needed alterations to the missile itself, including adding heavier and more lethal projectiles to the missile’s blast fragmentation warhead as well as reprogramming proximity fuse algorithms to optimize them for high-speed targets such as ballistic missiles. This addressed the PAC-1 missiles’ poor lethality versus ballistic targets.

Patriot’s troubled history

When the Gulf War erupted, the Patriot PAC-2 was brand new technology still in the process of being fielded. Patriot batteries in the Gulf War received a trial by fire. The Iraqis had a large number of Scud tactical ballistic missiles which managed to evade destruction by US air assets. In the course of the war, the Patriot engaged numerous Scud missiles while defending US positions and installations.

Initial US government reports on the Patriot in the Gulf War overstated performance dramatically. While officials claimed successful interception rates of over 90%, it is clear now that this was not the case. In fact, Patriot performance was rather poor. While the official combat record of the Patriot missiles in the Gulf War is still classified, research done by third parties as well as high-profile failures to intercept indicate that the Patriot batteries had serious difficulties countering Iraqi Scud missiles. Computer glitches, fuze issues, and guidance problems hampered Patriot’s effectiveness, in many cases by causing Patriot’s warhead to detonate without sufficiently damaging the target, making it seem that Patriot had achieved a hit when in fact the target’s warhead was still intact and deadly.

Patriot’s troubles during the Gulf War came to the public’s attention when a Patriot battery failed to intercept a Scud missile aimed at an army barracks, resulting in the death of 27 soldiers  The failure was later attributed to a rounding error in the Patriot’s fire control unit clock. This relatively minuscule discrepancy was significant only because of the high speeds of the missile as well as its target, which amplified the small error into a critical one.

The Gulf War Patriot debacle proved that ballistic missile defense was possible, but the extremely rapid speeds of the target, as well as the interceptor, meant that all components had to perform flawlessly in battlefield conditions.

To rectify the issues with Patriot PAC-2 uncovered in the Gulf War, development was ramped up. To improve PAC-2 lethality, many PAC-2s were upgraded to PAC-2 Guidance Enhanced Missiles (GEMs). PAC-2 GEMs feature a new digital fuze and guidance equipment, significantly increasing the probability of a kill on the target’s warhead. Raytheon engineers also made improvements to other components of the system, especially the electronics.

The biggest advancement, however, was the PAC-3 program, a massive departure from PAC-2 in terms of interceptor design. Patriot versions up to PAC-2 GEM featured launchers with four large missiles each. PAC-3 scrapped the quadruple launcher, instead using sixteen smaller interceptors. As a result, each Patriot battery can engage more targets before depleting its interceptor supply. The smaller missiles also facilitate maneuvering. Because of the size reduction, the PAC-3 missiles have a much shorter range than the PAC-2 missiles, which makes them less attractive for engaging traditional targets such as airplanes and helicopters, although they are still capable of doing so. The biggest PAC-3 improvement, however, was the usage of a new kill mechanism — instead of an explosive, PAC-3 interceptors destroy their target by simply crashing into it at immense speed, which removes the possibility of explosive fragments missing their targets or fuses failing to detonate appropriately. PAC-3 also improved radar and guidance performance through upgrades and software tweaks.

Recent Combat Success

While undoubtedly more capable in the missile defense role than previous Patriot iterations, the capabilities of PAC-3 and PAC-2 GEM still needed to be demonstrated in combat. The US Army tested the new Patriot equipment on a small scale during Operation Iraqi Freedom, achieving nine successful intercepts out of nine attempts.

The system received further validation recently, as Saudi Arabia, which operates both PAC-3 and PAC-2 variants, has used its Patriots during the Yemeni Civil War to intercept missiles fired by Houthi rebels. Many of the intercepted targets were derivatives of the USSR-designed Scud, one of the most common ballistic surface-to-surface missiles. Raytheon has claimed a 100% success rate for the Saudi Patriots across “[more than] a couple of dozen” intercepts. Astute observers will note that some Scud missiles did inflict damage upon Saudi Arabia and its allies — Raytheon’s statement implies these targets were not protected by Patriot batteries.

The success of Saudi Arabia’s Patriot batteries — assuming the Raytheon statement is accurate — is a landmark achievement. It is frequently assumed that missile defense is a messy and unreliable affair — while this is still largely true for some more ambitious systems (such as Ground-based Midcourse Defense), the Saudis’ experience demonstrates that mature tactical systems such as Patriot are fairly consistent in their performance. Nevertheless, Raytheon’s statement leaves a lot of important information still unknown, such as the nature of the targets intercepted and the methodology used to determine exactly what constituted a successful engagement.

For Raytheon, Patriot’s success in Saudi service could not come at a better time. Poland recently inked a deal to procure Patriot systems, and Germany is considering extending the service of the Patriot instead of adopting Lockheed Martin’s new MEADS system. In addition, PAC-3 Mid-Segment Enhancement (MSE), which boosts range by 15km and maximum altitude by 50%, is under development. The combat record of the Saudi Patriots will go a long way towards reassuring current and prospective Patriot customers that the system is capable of handling ballistic missile threats effectively and that funding MSE development is worthwhile. In addition, the Raytheon engineers will be able to use information gleaned by the Saudis to improve Patriot’s performance even further, and Patriot engineers can now boast that their PAC-3 design is extensively combat-tested.

However, the job of Patriot engineers is far from complete. While SCUD-type missiles are challenging targets, their underlying design is decades old. Russia and China have produced more modern missiles designed specifically to defeat US missile defense systems which Patriot has yet to face. For example, the Iskander tactical ballistic missile has onboard countermeasures and can execute high-g maneuvers to avoid interception. Patriot’s combat capabilities against these more sophisticated ballistic missiles remains unknown.