In today’s environment of accelerating technology, evolving threats and constrained resources, the Department of War (DOW) faces a central challenge: how to maintain battlefield dominance with increasingly complex platforms and systems — without becoming locked into proprietary solutions. The Modular Open Systems Approach (MOSA) offers a decisive path forward. More than a design preference, MOSA is a strategic imperative for the future readiness, adaptability and resilience of defense technology.

By embracing open system architecture — built around modular components, open standards and clearly defined subsystem boundaries — the DOW can rapidly integrate emerging technologies, reduce lifecycle costs and foster a competitive industrial base. These modular systems allow hardware and software components to be added, removed or upgraded independently, without requiring a full system redesign. This flexibility accelerates innovation, strengthens interoperability across services and allies, and enables a more agile partnership strategy with industry.

As emphasized in recent DOW modernization guidance, MOSA is not just about engineering — it’s about operational advantage. It empowers the DOW to move faster, spend smarter and stay ahead of adversaries in an era defined by technological disruption.

Multiple converging trends are driving the urgent need to address:

• Rapidly evolving threats and technologies
  Adversaries’ capabilities are accelerating across all domains. To counter these capabilities, systems must be upgradeable and adaptable. Closed, monolithic systems will be left behind. MOSA systems reduce development cycles and enable technology insertion more quickly. The ability to adapt faster than adversaries to replace or upgrade capabilities without wholesale system replacement will create a competitive advantage.
• Budgetary pressures and cost constraints
  Proprietary components, unique or custom interfaces, and vendor lock drive up life‐cycle costs. Open architectures enable reuse and competition among suppliers and discourage program designs that limit the ability to rapidly upgrade.
• CJADC2

Today’s battlefield is comprised of joint services, allies and multiple, all-domain platforms (air, land, sea, space, cyber) where interoperability is the foundation for C5ISR operations. Open standards and interfaces accelerate integration by enabling seamless collaboration with allies—regardless of the systems they use—and by supporting data and system interoperability across all domains.

• Rapid sustainment and upgrade
  Systems must not only be delivered, but sustained over decades through upgrades, patches, maintenance and emergent requirements. With open architectures, individual modules can be updated or replaced without redesigning the entire system. This will enable a more diverse industrial base.

Implementation challenges remain, and the DOW must address key issues to fully realize the benefits of MOSA.

• Standards governance and conformance: Open standards must be carefully designed, collaboratively developed, and rigorously enforced—while allowing industry to contribute and refine them over time. Defining interface standards and ensuring true interoperability among modules demands strong engineering discipline and robust oversight. To fully realize the benefits of MOSA, early planning and consistent coordination across programs are essential.
• Intellectual Property (IP) and data rights: Industry’s intellectual property and data rights can be safeguarded—up to the interface boundary. This approach preserves the DOW’s ability to operate, maintain and upgrade systems without incurring excessive royalties or facing restrictive licensing barriers.
• Legacy systems integration: Much of the DOW’s infrastructure is legacy; migrating or integrating with older systems can be complex, risky, and expensive. Transition to MOSA must be a part of each acquisition roadmap with incentives given to vendors who provide this architecture.
• Cybersecurity risks: Published interfaces and standards invite attack; rigorous security architecture within the individual components is table stakes. Continuous modification to platforms and systems also make it harder for adversaries to identify exploitable weaknesses.
• Cultural and contractual inertia: Emerging neo-defense tech firms, venture-backed defense technology, and small privately held startups are all built around proprietary solutions that drive exclusivity to help reduce future competition. It will take a few program successes to show how both industry and the DOW can both win.
• Certification, testing, and validation: Modular systems and plug‑and‑play components call for robust certification frameworks; especially in safety‑critical or mission‑critical systems. Building out, simplifying and democratizing access to government test labs and certification capabilities to validate conformance, interoperability and security of modules/components must be a priority.

Modern open system architecture is not just a technical preference—it is a strategic imperative. MOSA and similar frameworks align the DOW’s acquisition, engineering and sustainment paradigms with the realities of fast‑moving threat environments, stretched resources and the accelerating pace of technology.

In embracing open systems, the DOW can ensure its platforms, weapons and software remain relevant, competitive, upgradeable and interoperable—not only today, but decades into the future. The future battlefield demands architectures that are open by design, modular by purpose and secure by default.

MOSA is not just theoretical: it is codified into DOW acquisition policy and law for major U.S. defense acquisition programs. The DOW has also published software modernization strategies emphasizing speed, resilience and open‑architecture elements. The Army’s programs—such as the Enduring High Energy Laser and the C4ISR/EW Modular Open Suite of Standards—exemplify this forward-thinking approach to modular and interoperable system design.