For most of the modern military era, the electromagnetic environment has been something to work around. Terrain blocks line of sight, buildings scatter signals, weather degrades links, and clutter complicates sensing. Engineers responded by adding power, complexity, and redundancy. The environment itself remained fixed, an adversary or at best a neutral factor. Reconfigurable Intelligent Surfaces upend that assumption by making the physical world part of the system design.

RIS introduces the idea that walls, facades, vehicles, and infrastructure can be engineered to shape how electromagnetic waves move through space. Instead of adapting radios and sensors to an unpredictable channel, forces gain the ability to program the channel itself. This shift is arriving at a moment when armed forces are preparing for operations in heavily contested and congested spectrum environments, while also laying the groundwork for post-5G and 6G technologies. In that context, RIS are drawing attention not as a niche hardware innovation, but as a potential enabler of communications, sensing, and spectrum dominance.

At their core, Reconfigurable Intelligent Surfaces are planar structures composed of large arrays of engineered elements, often realized using metamaterials. Each element can dynamically adjust how it interacts with incident electromagnetic energy, controlling parameters such as phase, amplitude, or polarization. Coordinated across hundreds or thousands of elements, the surface can redirect signals toward friendly receivers, suppress or distort unwanted emissions, and enhance coverage in environments that would otherwise be denied or degraded.

What makes RIS particularly attractive for defense applications is their operational profile. These surfaces are typically low-power or nearly passive. They do not rely on continuous active transmission, which means they generate minimal electromagnetic signatures. Compared to traditional relays or jammers, they are harder to detect, harder to target, and more difficult to classify through conventional signal intelligence methods.

Although RIS are often described in terms of hardware and materials, their real impact lies in signal processing. Conventional military communications are built around adapting to the channel through waveform design, coding, diversity, and power control. RIS introduce a different paradigm in which the channel becomes a controllable resource. This changes the role of signal processing from reactive optimization to proactive environment shaping.

Making this possible requires solving a new set of technical problems. The effective use of RIS depends on estimating high-dimensional channels that include not only the direct link between transmitter and receiver, but also cascaded paths involving the surface itself. It requires real-time optimization of surface configurations under mobility, interference, and adversarial conditions. These problems are computationally demanding and tightly coupled to the physical behavior of the hardware. Advanced digital signal processing techniques, increasingly augmented by machine learning, are central to enabling adaptive control that is fast enough and robust enough for operational use.

In communications, the benefits align closely with current military needs. RIS can extend connectivity in dense urban terrain, underground facilities, and mountainous regions where traditional line-of-sight links are unreliable. By redirecting existing signals rather than emitting new ones, they support low probability of intercept and low probability of detection objectives. Dynamic reconfiguration of the surface enables rapid adaptation to jamming or interference, improving resilience in contested spectrum conditions. At higher frequencies such as millimeter-wave and terahertz bands, RIS help overcome severe path loss and blockage, making these wideband technologies more viable for tactical and strategic networks.

The influence of RIS is not limited to communications. They are increasingly viewed as a key component of integrated sensing and communication architectures, a trend gaining momentum across defense research. By shaping reflections and multipath propagation, RIS can improve radar detection and tracking performance in complex environments. They can enhance situational awareness without the need to deploy additional active sensors, supporting passive or semi-passive sensing approaches that reduce emissions and improve survivability. In surveillance and border security applications, RIS effectively act as electromagnetic force multipliers, increasing sensing performance while minimizing additional hardware footprint.

Electronic warfare is another domain where RIS challenge established concepts. Traditional EW focuses on emitting energy to jam, deceive, or overwhelm adversary systems. RIS suggest a complementary approach in which forces influence how electromagnetic energy propagates through space. By shaping the environment rather than transmitting counter-signals, RIS support defensive electronic warfare and spectrum protection while remaining difficult to detect. Although many of these ideas remain experimental, they point toward a future in which control of space is as important as control of transmitters.

Significant challenges remain before RIS become a standard element of defense systems. Practical implementations must contend with hardware limitations such as finite phase resolution and non-ideal element behavior. Control latency, synchronization across large surfaces, and the scalability of real-time optimization algorithms are ongoing concerns. Systems must also operate reliably under harsh environmental and operational conditions. Addressing these issues demands close integration between signal processing, artificial intelligence, and hardware-aware design.

Despite these hurdles, the strategic implications are difficult to ignore. RIS represent more than an incremental improvement in radios or sensors. They point toward a shift in doctrine, where future operations involve not only managing platforms and networks, but actively programming the electromagnetic environment. As research moves from laboratories to fieldable systems, RIS are likely to influence next-generation C4ISR architectures, smart bases and forward operating environments, and spectrum-dominant operations across multiple domains.

By turning ordinary surfaces into adaptive electromagnetic assets, Reconfigurable Intelligent Surfaces redefine how signal processing intersects with defense technology. In an era where information superiority increasingly depends on mastery of the electromagnetic domain, the ability to shape that domain itself may prove to be one of the most consequential capabilities of the coming decade.