Anduril unveils Steelfin missile to slash US air defense costs and challenge Patriot PAC-3 and THAAD.

On October 12, 2026, Anduril Industries unveiled the Steelfin, a scalable family of modular surface-to-air interceptor missiles designed to defend U.S. forces against drones, cruise missiles, ballistic missiles, and maneuvering hypersonic weapons. The architecture employs a two-stage configuration featuring a common terminal interceptor paired with interchangeable solid-propellant boosters to optimize manufacturing scalability. This system targets reduced procurement costs and expanded inventory availability for sustained combat operations across existing military launchers.

Anduril’s new Steelfin is a modular family of surface-to-air missiles designed to counter drones, cruise missiles, ballistic missiles, and hypersonic threats at a lower cost than existing U.S. air defense missiles. (Picture source: Anduril)

On October 12, 2026, Anduril unveiled the Steelfin, its first family of surface-to-air interceptor missiles, to reduce the cost of defending U.S. forces against drones, cruise missiles, ballistic missiles, and maneuvering hypersonic weapons while increasing missile availability for sustained combat operations. Intended to compete with the Patriot PAC-3 MSE, SM-2, and THAAD missiles across different missions, the Steelfin features a two-stage architecture combining a common terminal interceptor with three interchangeable solid-propellant boosters measuring 10 inches (254 mm), 18 inches (457 mm), and 21 inches (533 mm) in diameter, allowing different guidance systems, propulsion configurations, and warhead options to be adapted to specific threats.

Anduril aims to offer these interceptors at lower prices than existing missiles, which cost approximately $2.5 million for the SM-2 Block IIIC, $5.3 million for the PAC-3 MSE, and $15.5 million for THAAD. Following initial ballistic trials, the Steelfin is scheduled to begin flight testing in 2027, with full-rate production targeted for late 2028 or early 2029. The company plans to manufacture several thousand missiles annually during the initial production phase, with configurations designed for integration into existing U.S. Army and U.S. Navy launchers. The Steelfin's 10 inches booster fits the U.S. Army's Future Interceptor requirement for a 254 to 330 mm booster paired with a 178 to 254 mm terminal interceptor. The larger 457 and 533 mm boosters would support different propulsion and engagement requirements, with the largest matching the nominal diameter of the SM-3 Block IIA.

Related topic: Lockheed Martin unveils PAC-3 ACE interceptor to cut Patriot missile cost in half amid global shortages

All variants of the Steelfin would share the same basic avionics, software, flight controls, and mechanical interfaces, while accommodating different propulsion and seeker arrangements for individual missions. For instance, radar seekers would permit active radio-frequency target acquisition and tracking, while infrared seekers would use thermal signatures for terminal guidance. Hit-to-kill configurations would require direct collision with the target, whereas blast-fragmentation warheads would use an explosive payload to damage the threat within the lethal radius. Rocket motors would come from Anduril and external suppliers, and Anduril already targets supersonic-to-hypersonic speeds and low-to-high endoatmospheric missions, but has not disclosed launch mass, thrust, range, velocity, or interception altitude. 

The smallest Steelfin missiles are intended to counter Shahed-type one-way attack drones without expending more expensive surface-to-air missiles when radar coverage, reaction time, and launch geometry are sufficient. Intermediate versions would engage aircraft and low-altitude cruise missiles, including those approaching through terrain or radar-cluttered environments, requiring reliable target tracking. Finally, the larger Steelfin variants would address tactical ballistic missiles during terminal descent and potentially maneuvering hypersonic weapons inside the atmosphere. These missions require different acceleration, guidance accuracy, and maneuvering performance, particularly against ballistic targets with high closing velocities and shorter opportunities for correction during the final engagement.

Hypersonic threats add the requirement to intercept targets capable of maneuvering at high speed, which complicates the prediction of their future position. Anduril has not assigned specific configurations to verified engagement ranges or target speeds, and the future Steelfin flight test has yet to demonstrate an interception against any of these target categories. Anduril's proposed integration with existing launchers is particularly relevant for U.S. forces during a prolonged engagement, as the Steelfin is intended for the Patriot M903A2 launcher, the Mk 41 Vertical Launch System (VLS), the Typhon Mid-Range Capability (MRC) system, and the Common Autonomous Multi-Domain Launcher (CAML), while being compatible with fire control systems such as the Aegis and the Integrated Battle Command System (IBCS). The U.S. company is also considering dual-packed and quad-packed configurations for each Mk 41 cell, although larger Steelfin variants would not necessarily fit these arrangements.

On an Arleigh Burke-class destroyer with 96 Mk 41 cells, allocating 32 cells to Steelfin missiles would leave 64 for SM-3s, SM-6s, Tomahawks, or anti-submarine weapons, which could reduce the need to return to port for ammunition replenishment during repeated drone or cruise missile attacks. Still, it would not logically increase the ship's radar capacity or the number of engagements its combat system can manage simultaneously. The proposed unit costs illustrate why Anduril is pursuing different configurations rather than a single interceptor intended for every threat. Anduril says its Steelfin is intended to deliver approximately 80% of the PAC-3 MSE's mission capability at less than half its cost, with a more ambitious objective of approximately one-third the price. Using the U.S. Army's FY2027 PAC-3 MSE benchmark of $5.3 million, those targets imply less than $2.65 million or approximately $1.77 million per interceptor, respectively.

For missions currently assigned to the SM-2, Anduril targets more than 80% of its capability at approximately one-third the cost, equivalent to $833,000 against a $2.5 million SM-2 Block IIIC benchmark. These are Anduril's development and pricing objectives, not confirmed selling prices. The company has not published a fixed price for each Steelfin configuration, and its capability percentages have not been demonstrated through comparative interception tests. Anduril's Stephen Milano also claims that a higher-end Steelfin could perform 100% of the THAAD mission at a fraction of its $15.5 million price tag, although no specific price has been announced for that variant. But these claims prove that Anduril is proposing different price-to-capability ratios for each Steelfin variant, rather than promising that every version will cost one-third as much as the PAC-3 MSE.

Manufacturing capacity now represents a separate requirement from missile performance, particularly because the United States is seeking to replenish stocks while maintaining supplies to allies. Anduril intends to manufacture most Steelfin subassemblies at its Arsenal-1 facility in Ohio, followed by final integration with selected industrial partners. Production would use common tooling, terminal-stage components, avionics, and assembly processes, with different boosters and seekers incorporated according to customer requirements. Stephen Milano, Anduril's senior missile development executive, expects full-rate production in late 2028 or early 2029, with an initial output of multiple thousands of missiles annually and a longer-term ambition potentially reaching hundreds of thousands if orders justify the investment. For instance, a rate of 5,000 interceptors annually would require 417 completed missiles per month, compared with 167 per month under the U.S. government's target of 2,000 PAC-3 MSE missiles annually.

However, the two production figures are not directly equivalent because the Steelfin would include configurations with different propulsion, guidance, and interception requirements. Anduril intends to manufacture some solid rocket motors internally and obtain others from external suppliers, using interchangeable mounting interfaces to reduce dependence on a single motor manufacturer, and this would diversify procurement options. The Steelfin also enters several overlapping U.S. acquisition efforts that have different performance and cost requirements. The Army's May 15, 2026 MOSAIC-26-03 initiative targets a complete Patriot-compatible interceptor costing less than $1 million, with separate objectives of $250,000 for rocket motors, seekers, and fire control components.

The requirement includes compatibility with the Patriot M903 launcher and IBCS, a minimum Technology Readiness Level of 6, and engagements against cruise missiles, air-breathing targets, and short-range ballistic missiles. Anduril also advanced into the testing and demonstration phases of the U.S. Army's $8 million xTech Apex Intercept competition, alongside companies including AeroVironment, AirX Robotics, Cambridge Aerospace, and X-Bow Systems. The separate Future Interceptor effort seeks to fill the engagement gap between PAC-3 MSE and THAAD missiles: Lockheed Martin and an undisclosed competitor have advanced in that competition, while Anduril has declined to confirm whether the Steelfin was selected.

Lockheed Martin is simultaneously developing the PAC-3 Adapted Capability Effector (ACE), introduced in July 2026 with a price objective below half that of PAC-3 MSE, and PAC-3 Edge, unveiled on October 9, with a new seeker, upgraded flight controls, and a multi-pulse rocket motor for longer-range and higher-altitude engagements. The Navy's Naval Modular Missile initiative also pursues a common terminal interceptor with interchangeable boosters and canisters, including multiple missiles per Mk 41 cell and configurations for Virginia-class submarines equipped with Virginia Payload Modules, with an annual production target of 1,000 units within five years of contract award. This U.S. interceptor expansion responds to multiple severe missile expenditures.

In the Middle East, Iranian missile and drone attacks have required U.S. and allied forces to expend defensive missiles against simultaneous threats, while Ukraine's continued use of Patriot interceptors against Russian ballistic and cruise missiles places additional pressure on available inventories. A conflict with China could extend these demands across multiple airfields, naval bases, logistics facilities, and deployed warships in the Western Pacific, requiring interceptors to be distributed among geographically separated defensive positions, and amid a continuing Patriot demand in Ukraine. Therefore, a framework was established in January 2026 to increase PAC-3 MSE annual capacity from 600 to 2,000 missiles, with a $4.7 billion accelerated-production action on April 10 and a longer-term agreement worth up to $58.6 billion.

Separately, X-Bow received $10.9 million to develop a ballistic missile interceptor costing less than $750,000, with a late-2027 flight demonstration planned, while the Navy's September 2026 Naval Affordable Interceptor initiative seeks at least 60 missiles per containerized launcher, production capacity of 500 annually, and deployment within 12 months of contract award. These investments indicate that the U.S. is pursuing a combination of increased PAC-3, SM-3, and SM-6 production, higher-performance weapons such as PAC-3 Edge, and lower-cost missiles for engagements that do not require the most expensive defensive ammunition, which could include the Steelfin.

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Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, South Korea, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.