The authors of this report explore passive defense's relevance to modern conflict. They outline a process that the Joint Staff could use to (1) identify gaps, (2) generate new concepts and investment options, and (3) assess the value that those passive defense measures might provide to improve outcomes in high-priority conflict interactions, and the authors discuss some of the factors to consider when doing so.

Passive Aggressive

Reconsidering the Relevance of Passive Defenses in Major War

Michael J. Lostumbo, Karl P. Mueller, Mark Hvizda, James Bonomo, William Kim

ResearchPublished Dec 11, 2025

The Joint Staff asked RAND to develop a new framework around passive defenses and suggest ways that the Joint Staff could assess those capabilities to determine whether such capabilities can contribute to achieving national-level goals of deterring major conflict in the Pacific and in Europe or to prevailing in major conflicts if deterrence fails.

The authors reviewed guidance documents and U.S. military doctrine to identify key national goals and the military approach to meeting those goals, as well as definitions and concepts related to passive defenses. They considered recent conflicts involving the U.S. military for examples of situations in which defenses were particularly important. Using those assessments, they developed a framework to better understand the value of passive defenses to the modern U.S. military.

Key Findings

  • Protecting the force is always relevant: Even militaries with very aggressive doctrines of maneuver warfare are exposed to attrition and will seek ways to mitigate such vulnerabilities.
  • Passive defenses are being used extensively in the conflict in Ukraine. Whether this is relevant to future U.S. operations depends on assumptions about how the different U.S. military tactics and capabilities that are likely to be employed in future conflicts might solve some of the problems that require passive defense investments.
  • For passive defenses to be relevant in future conflicts, they should be closely tied to protecting forces from the modern kill chain and the effects of the precision weapons that the kill chain delivers.
  • To deter future major-power conflict, passive defenses need to convince the adversary that its preferred mode of attack is overly risky and unlikely to succeed.
  • Adversary anti-access/area denial investments are specifically designed to attrite elements of the U.S. force that are seen as key to victory, so understanding the resilience of the force to these threats is critical to being fully prepared for such challenges.
  • In Ukraine, small unmanned aerial systems are demonstrating that new technology developments are holding at risk different types of forces in different ways, sparking urgent efforts to mitigate these new vulnerabilities.
  • The Joint Staff has an important vantage point to help coordinate efforts across the U.S. Department of Defense, including working with partners.

Recommendations

  • The U.S. Department of Defense should revise the definition of the term passive defense to better link it to the task of countering the adversary kill chain and minimizing weapon effects.
  • Using national-level guidance on deterring future conflict, the Joint Staff should identify ways that passive defenses could contribute to making a potential adversary doubt the success of its preferred course of attack.
  • The U.S. military should identify the critical conditions for success in priority scenarios and the vulnerabilities of enemy and friendly forces to determine how passive defense investments might improve outcomes and contribute to war-winning capabilities.
  • The Joint Staff should work with partners and allies in the Pacific and the North Atlantic Treaty Organization so that it can benefit from available expertise regarding passive defense options to help develop integrated plans of action.
  • The Joint Staff should develop an analytic assessment plan, including fundamental research relevant to adversary weapons and adversary kill chains, and develop and assess concepts and capabilities for providing passive defenses to mitigate key vulnerabilities.

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Document Details

Citation

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Lostumbo, Michael J., Karl P. Mueller, Mark Hvizda, James Bonomo, and William Kim, Passive Aggressive: Reconsidering the Relevance of Passive Defenses in Major War. Santa Monica, CA: RAND Corporation, 2025. https://www.rand.org/pubs/research_reports/RRA2955-1.html.
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This research was sponsored by the Joint Staff and conducted within the International Security and Defense Policy Program of the RAND National Security Research Division (NSRD).

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