The expanding zone where homes meet wildland vegetation—known as the wildland–urban interface (WUI)—presents significant structural risk during wildfire events. Research shows that most structure losses in WUI fires result from ember transport, radiant heat, and flame contact. To reduce these risks, mobile Structure Protection Units (SPUs) are emerging as key tactical resources. Equipped to deliver active defence around structures, SPUs strengthen WUI resilience by providing scalable, pre-emptive, and mobile protection during wildfire events. Understanding SPUs in the WUI Context SPUs are typically trailer-mounted or mobile assets equipped with pumps, hoses, sprinklers, and rapid-deployment systems. They enable agencies, utilities, and property managers to quickly establish a defended perimeter around structures or neighborhoods in the WUI. During fast-moving wildfires, standard fire engines may struggle with water constraints, long hose-lays, or rough terrain. SPUs fill that gap by providing dedicated structure-protection capabilities with independent water-delivery systems. As of 2018, about one-third of U.S. housing units were located in WUI zones—further underscoring the importance of scalable protection strategies like SPUs. How SPUs Strengthen WUI Resilience 1. Pre-emptive Wetting and Humidity Control SPUs deploy sprinkler networks that wet roofs, siding, vegetation, and defensible-space zones. This reduces ignition potential from embers and enhances overall structure defendability. 2. Rapid Staging and Strategic Defence By positioning SPUs in advance of the fire front, responders gain quicker readiness and safer deployment conditions. Mobile SPUs can serve at access points, interface lines, or vulnerable infrastructure corridors to improve response timing. 3. Scalable, Multi-Structure Defence SPUs can defend clusters of properties or critical infrastructure simultaneously. Some units are configured to protect dozens of structures, making this approach cost-efficient for agencies and municipalities. 4. Integration with Existing Mitigation SPUs complement defensible-space programs, resistant construction standards, and community planning. They work best as part of a layered strategy combining passive prevention with active suppression tools. 5. Improved Responder Safety Pre-staged SPUs reduce the need for rushed, high-risk deployment in dynamic fire zones. They streamline operations and contribute to safer, more organized tactical responses. Key Considerations for Stakeholders Risk mapping: Prioritize structures based on exposure type and access limitations. Water supply: Ensure SPUs have reliable access to tanks, hydrants, or tenders and proper pump sizing. Mobility logistics: Optimize trailer configurations, staging sites, and deployment times. Operational protocols: Define SOPs for activation, ICS integration, and structure-defence coordination. Maintenance: Regularly test pumps, hoses, sprinklers, and trailers for readiness. Integration: Align SPU use with defensible-space programs, building codes, and community outreach. Performance metrics: Track structure survival rates, deployment efficiency, and overall impact. Limitations and Practical Realities SPUs supplement but do not replace foundational wildfire mitigation measures. Effectiveness depends on access, fuel conditions, and water availability. Proper timing and staging are critical for successful activation. Cost and staffing must align with the risk profile of the target zone. Every WUI area has unique risks that should inform SPU deployment design. Final Thoughts For communities, utilities, property owners, and fire agencies operating in WUI zones, Structure Protection Units provide a powerful defence layer. Their mobility, scalability, and precision make them invaluable assets for reducing structure loss and improving firefighter safety. Deployed as part of a comprehensive WUI strategy—combining defensible space, building hardening, and proactive planning—SPUs play a critical role in strengthening resilience across the wildland–urban interface.