An MQ-9 Reaper drifts ominously through the crisp, pre-dawn sky over Sanaa, Yemen. Its matte-gray fuselage blends seamlessly with the deepening hues of early morning, its whirring sensors casting an invisible gaze over bustling streets below.
Thousands of miles away, in a dimly lit control room, the pilot leans back in his chair, the glow of monitors casting sharp lines across his face. He reaches for his paper coffee cup and slowly brings it to his mouth. “Another slow night,” he murmurs — the words barely escaping his lips before the screen flickers. Static. Silence. Panic hits his chest as he scans his panel, unaware that his $30-million aircraft is now a blazing comet falling to the Earth in pieces.
In an operations center half a world away, analysts erupt into motion, voices colliding as they attempt to piece together what happened. No clues. Hours later, a video emerges, confirming what many had begun to suspect.
This is no future battlefield bristling with radar-guided missiles. This is a quieter menace, a shadow war waged by something far more elusive and insidious: a passive integrated air defense system. Operating unseen, it strikes without warning, rewriting the rules of air superiority in silence.
On Jan. 12, 2024, U.S. forces, with support from other countries, conducted a strike targeting Houthi radar systems, air defense infrastructure, and weapons storage facilities in the Red Sea region. Despite these efforts, the Houthis claim to have downed 14 U.S. MQ-9s since Oct. 7, 2023. Their military parades and close ties to Iran reveal a critical enabler: passive air defense systems.
The challenge posed by passive defenses is not new. These systems have advanced alongside the evolution of the air domain. From the crude anti-aircraft artillery of World War I to today’s cutting-edge passive radar systems, each innovation has provoked the same refrain: “That’s going to be scary to go against.” Yet, despite decades of warnings, the Department of Defense has done little to address these threats proactively.
The Houthis’ abilities to degrade U.S. air assets are quickly becoming lessons for the adversary, underscoring a harsh reality: The credibility of American deterrence is eroding. Effectively countering the current passive air defense threat is crucial for restoring deterrence and ensuring credible defenses for allied nations. To do this, policymakers, leaders, and commanders need to come together to overcome distorted views, understand the threat at hand, and accept the creative solutions that tactical operators propose.
Distorted Views of Air Superiority
The long 9/11 wars in Iraq and Afghanistan were fought against adversaries without sophisticated air defenses, allowing unfettered air operations and target engagement. This fostered complacency, undermining a focus on air superiority and neglecting the tools and training needed to maintain it. This inadequacy is evident in Yemen, where Houthi air defense systems continue to expose the limitations of outdated strategies. The proliferation of advanced systems and the demonstrated inability to counter them predict similar vulnerabilities in future conflicts. Without adopting new techniques to eliminate these threats, air superiority will remain unattainable, and combat-proven tactics will lose relevance.
Former Secretary of Defense Jim Mattis said that “doctrine is the last refuge of the unimaginative.” The U.S. military’s over-reliance on established practices often stifles creative problem-solving. Understanding an adversaries’ motivations, capabilities, and intentions is essential for developing effective strategies and tactics. Future conflicts with adversaries like Iran or China will demand unprecedented and adaptive approaches.
Preparation for these conflicts has unfortunately devolved into a global arms race. America’s preference for costly stealth platforms reflects an emphasis on quality over quantity, a miscalculation evident in historical conflicts. From the attritional strategies of World War II to the Taliban’s endurance in Afghanistan, quantity has frequently outperformed high-cost precision. The war in Ukraine illustrates the battlefield success of low-cost technologies, such as single-use drones. These innovations negate the need for advanced fighter aircraft to penetrate enemy airspace. Despite these lessons, reliance on stealth technology persists, ignoring vulnerabilities to passive radar and electro-optical/infrared detection systems. Adversaries continue investing in low-cost, effective systems that erode America’s technological advantage. To regain the initiative, the Department of Defense should prioritize scalable, cost-effective solutions that counter emerging threats. The survivability of passive air defense systems in conflict ensures extended engagements that the United States is currently ill-prepared to endure.
Understanding the Threat
Integrated air defense systems are designed to detect, track, and neutralize airborne threats through three core functions: air surveillance, battle management, and weapons control. Traditional air defense systems rely heavily on active radars to transmit radio frequency signals and detect returns from potential targets. Such emissions, while effective, are highly exploitable by U.S. space-based or tactical airborne sensors. However, passive integrated air defenses leverage multiple techniques to reduce the likelihood of destruction such as camouflage, concealment, dispersion of forces, rapid mobility, and strict communication security. However, the key difference is avoiding or severely limiting the use of active military radars.
At the core of any integrated air defense system is air surveillance, tasked with detecting aircraft, initiating and maintaining tracks, identifying threats, and correlating data with other sites. Traditional systems achieve this through active radars, but passive systems leverage infrared, acoustic, and electromagnetic sensors as well as other advanced techniques. These sensors detect heat, noise, and electronic signals emitted by aircraft. Some advanced passive radars can also detect disturbances in ambient civilian signals, such as radio and television broadcasts, that are created as aircraft travel through the sky. Passive integrated air defense systems may also tap into civilian air traffic control radars that are not immediately identified as providing a military function. Belligerents may also receive aircraft tracking information from countries that the United States is not currently in conflict with. In their simplest form, passive integrated air defenses may deploy visual observers equipped with binoculars to monitor predictable air corridors. These methods, combined with camouflage and concealment, make passive air surveillance nodes extremely difficult to detect and disrupt.
Information collected by air surveillance sites is then relayed to battle management centers through a variety of communication links, including landlines, satellite communications, and digital radios. While modern integrated air defenses prioritize secure, automated data sharing with built-in redundancies, these transmissions remain vulnerable to exploitation. At the battle management centers, data from multiple sensors is fused into a cohesive air picture. Here, human operators assess and prioritize threats, determine engagement authority, and select weapon systems. These decisions rely on sophisticated command-and-control suites but remain subject to delays or errors by human operators who may be under immense pressure, particularly when managing multiple threats.
The final step, weapons control, involves engaging detected threats. Traditional systems again rely on active radars to generate target-quality tracks and guide missiles to their targets. Passive systems, by contrast, tend to employ undetectable electro-optical and infrared tracking and guidance, robbing airborne assets of receiving advanced indications and cutting down their time to react. Because of their reduced detectability, passive systems can afford to let targets get in close, reducing the engagement timeline and further limiting the aircraft’s ability to defend. Passive integrated air defenses may also utilize systems that rely on limited active emissions that remain difficult to locate but may be more capable at engaging fighter aircraft. Heat-seeking systems also maintain their effectiveness against stealth platforms that are specifically designed to counter radar systems.
The rise of passive integrated air defense systems represents a fundamental challenge to U.S. air superiority. Traditional tactics, such as using anti-radiation missiles to neutralize active radar systems, are largely ineffective against passive systems. These systems reduce the detectability of their components, complicating the find, fix, track, target, engage, and assess process that underpins U.S. targeting doctrine. An infrared camera placed on a residential rooftop, or an acoustic sensor hidden in a civilian vehicle is far more challenging to locate than a traditional radar site.
Despite these challenges, passive systems are not without vulnerabilities. Air surveillance nodes should still communicate with battle management centers, creating exploitable data links. Missile launches generate heat signatures possibly detectable by overhead satellites and onboard systems of select aircraft, offering opportunities for counterstrikes. Moreover, passive systems often rely on single engagements, making them susceptible to saturation tactics or coordinated attacks by multiple aircraft.
Strategic leaders ought to understand the threats that they face today but also look to prepare their forces for the future fight, which will likely involve a mix of passive and active systems. This mindset will allow them to promptly accept the solutions proposed by the operational elements that are closer to the fight. As former Delta Force commander Pete Blaber said, “Always trust the guy on the ground.”
Defining the Tactical Problem
The ability to affect an adversary’s will to wage war hinges on identifying and targeting their critical centers of gravity. This traditionally relies on extensive intelligence collection sometimes involving tactical airborne intelligence, surveillance, and reconnaissance platforms operating near potential targets. However, air defense systems deny aircraft access to the airspace, quickly shifting the priority to neutralizing these threats first.
Passive integrated air defense systems undermine traditional find-and-fix workflows mainly by minimizing their detectability. These systems can integrate seamlessly into civilian infrastructure, making them difficult to locate and neutralize without risking collateral damage. To counter these systems and regain air superiority, U.S. forces should focus on and target the more easily detectable enablers of passive integrated air defense systems. Patterns should be built to identify and prosecute the communication nodes that are associated with the passive air defense kill chain.
Passive integrated air defense systems present a novel problem set requiring novel solutions that have not been seen or practiced before at scale. Decision-makers are obligated to understand the urgency for these innovations and operational commanders should become comfortable authorizing the use of new tactics.
Novel Solutions
Addressing the passive integrated air defense threat begins with modernizing existing platforms to operate effectively in contested environments. For platforms like the MQ-9, this means equipping them with missile approach warning systems that can detect missile launches and flare dispensers that can defeat infrared-guided missiles. Additionally, extending sensor ranges would enable stand-off intelligence collection, mitigating risks associated with hostile airspace.
Modernization should also focus on munitions and other sensor capabilities. For instance, adapting the AGM-88 High-Speed Anti-Radiation Missile to target broader emissive signatures — such as communication nodes or battle management systems — would expand its utility in degrading passive air defense networks.
Innovative tactics, techniques, and procedures are essential for addressing the unique challenges posed by passive integrated air defense systems. Examples include: operating MQ-9s in two-ship or larger formations to provide mutual support and complicate enemy targeting solutions; deploying fighter escorts to protect collection platforms and enable extended operations in contested areas; expanding the target set of the Wild Weasels (specialized teams that traditionally find and target enemy active air defenses) to include passive air defense networks; and coordinating deliberate collection operations to identify critical centers of gravity within the passive air defense network for subsequent violent or non-violent operations. Lastly, aircraft should limit or mask their emissions to reduce detectability. This, however, complicates battle tracking by U.S. operation centers and deconfliction amongst tactical assets making it crucial to conduct thorough mission planning to avoid fratricide. One tactic remains certain: continuing to fly single MQ-9s in non-permissive airspace will only result in more MQ-9s being shot down.
Cyber operations, electronic warfare, information operations, and space assets offer cost-effective, flexible approaches to disrupting passive systems. By integrating these with strike options, the United States can achieve layered effects that degrade passive air defense capabilities without escalating risk to personnel or assets.
The United States and its allies should develop robust sensing and targeting grids tailored for contested environments. These networks would leverage affordable, scalable platforms — such as maritime drones, unattended ground sensors, and small unmanned aerial vehicles — to saturate the battlespace. Some advanced systems are capable of near-real-time detection and tracking. These systems, along with satellite communication links, facilitate rapid information sharing and cross-cueing of collection assets. Drawing lessons from historical initiatives like Operation Igloo White, modern sensor networks can achieve superior situational awareness and accelerate kill chains.
The critical element in any air defense system, passive or active, is human operators. Credible threats to their safety can deter them from risking their lives to shoot at an aircraft. The United States can only buy back military credibility through force. The cost of a downed MQ-9 should not be counted by the enemy in dollars. It should be counted in the number of fighters they lost that day.
A New Operational Paradigm
It is time to start taking the passive air defense problem seriously. The Houthis present a unique opportunity for the United States to test and refine novel technologies and techniques, providing valuable insights for countering more sophisticated adversaries like China and Iran. Lessons learned from this theater should be captured, analyzed, and applied properly to future operational planning.
The emergence of passive integrated air defenses requires a fundamental shift in how the United States approaches military power projection. The days of the United States being able to dominate enemy airspaces are numbered. The military should be prepared to leverage a multitude of capabilities and adapt techniques that can provide finite windows in which to operate, and to capitalize on those opportunities. While adversaries gain ground with low-cost technologies, the United States can maintain its edge by embracing innovation, modernizing platforms, and adopting multi-domain solutions.
Re-establishing a credible posture against highly capable adversaries will call for sustained, coordinated, whole-of-government efforts by the United States and its allies. Policymakers should understand the threat facing U.S. power projection, fund decisive modernization, and sign off on critical operations to recapture U.S. dominance. Strategic leaders should communicate this message to Washington and empower their operational commanders to take chances on new strategies. Finally, operational commanders should trust warfighters to develop and execute novel tactics to recapture the offensive. Addressing the Houthi passive air defense challenge today will prepare the United States for the acute and pacing threats of tomorrow, ensuring sustained operational superiority in the face of evolving adversaries.
Aaron “GHOST” Chambers is an Air Force officer serving as the intelligence operations officer at the Intelligence, Surveillance, and Reconnaissance Division at the 609th Combined Air & Space Operations Center.
William Mitchell is an Air Force officer serving as an intelligence analyst at the 609th Combined Air & Space Operations Center.
David “WACO” Bradfield is an Air Force officer and the current chief of weapons and tactics at the 609th Combined Air & Space Operations Center.
The views in this article are those of the authors and do not represent the views and positions of the U.S. Air Force, the Department of Defense, or any part of the U.S. government.
Image: U.S. Air Force
Jesus Christ is King
