Modular Open System Architecture (MOSA): A Path to Continuous Weapon Upgrades

A series of posts from the former Deputy Under Secretary of Defense for Acquisition and Sustainment, Al Shaffer, looks at pathways to drive innovation and modernization for national defense. Read the first blog in the series.

Fielding capabilities rapidly was central to Secretary Hegseth’s November 7, 2025, memo “Transforming the Warfighting Acquisition System."  In short, the Department is seeking to meet mission needs of a rapidly evolving battlespace one that puts fielding capabilities rapidly above all other attributes.  To address this, the Pentagon should adopt a development strategy like civilian industry, one that allows rapid and continuous deployment.  To meet this, the Pentagon has turned to Modular Open System Architecture (MOSA) and Sensor Open Systems Architecture (SOSA) as a key enabler.  This engineering architectural change is a key strategy for achieving faster, more cost-effective, and flexible capability development and upgrades.  Simply, with MOSA, the developer fields what is ready today and upgrades when new capabilities or modules mature. 

As a commercial analogue, consider the Apple iPhone.  Apple builds a system with a core operating system that allows any vendor meeting a specific interface standard to introduce new “apps”.  This opens the developer base to everyone from traditional software houses to small “Mom and Pop” garage operations.  The vendor base is democratized.  In short, shifting to MOSA/SOSA provides the promise of the Pentagon fielding what is available today with rapid upgrades as they become available. 

In December 2024, the three Service Secretaries (Army, Navy, and Air Force), signed a Directive that all major acquisition programs would use MOSA/SOSA to develop major new capabilities.  This is also a tenet of the new administration, as shown by Secretary Hegseth directing use of MOSA in his November 7 memo.

Key Government Policies and Directives Related to MOSA

The National Defense Strategy (NDS) identifies MOSA as an essential tool for transforming the Pentagon’s approach to capability development. The NDS emphasizes the need to field new capabilities faster and with greater flexibility to modify systems once fielded. This shift is driven by the recognition that adversaries are developing and fielding capabilities at a much faster pace than the U.S., necessitating a more agile and responsive acquisition system.

Description of MOSA and Its Current State of Use in the Pentagon

MOSA represents a paradigm shift from the traditional acquisition approach, which relies on tightly integrated or closed systems specified by the prime contractor with custom-designed connections between platform components. In contrast, MOSA uses standardized connections between major parts of a system, allowing for the easy removal and replacement of components, subsystems, and software. This "plug-and-play" approach enables regular technological upgrades of specific components without the need for wholesale changes to the design of the platform.

The Pentagon is making significant progress in adopting MOSA. For example, MOSA requirements were important considerations in the Army's selection of the XM30 Mechanized Infantry Combat Vehicle and the Future Long-Range Assault Aircraft. The Air Force's Next Generation Air Dominance Program is planned to be a "Fully Open System of Systems Architecture," and the Navy is procuring systems like the Air and Missile Defense Radar using open systems.  The most telling is the new Army M1E3 Abrams Tank upgrade, which was delivered in Dec 2025—5 years ahead of schedule.  The M13E was build on a digital backbone and MOSA components.  Nearly all other “parts” of the tank (cockpit, transmission, etc.) were commercially procured at a much lower price. 

Current Challenges in Accelerating Technology Adoption

The primary challenge in accelerating technology adoption within the Pentagon is the slow and cumbersome traditional acquisition process. This process often results in the development of "perfect" systems that take generations to field, leaving the U.S. at a disadvantage compared to adversaries who can field new capabilities much more rapidly.   In the old paradigm, largely driven by not having a near peer rival, the government spent a great deal of time trying to field the perfect system.  A case in point is the F-35 Joint Strike Fighter.  The program started in the early 1990s and achieved IOC in 2016, for a system the GAO estimates will be in the inventory for almost 90 years.  The F-35 is not an open system, and is very costly to upgrade.   The need for a more agile and responsive acquisition system is critical to maintaining the U.S. technological edge.

Reforms Already Undertaken

To address these challenges, several reforms have been implemented. In 2020, the Pentagon introduced the "Adaptive Acquisition Framework," (AAF) which provides tailored acquisition pathways for different types of capabilities. This framework includes new pathways for Middle Tier of Acquisition, agile software development, and urgent acquisitions, all designed to increase acquisition flexibility. Additionally, the Planning, Programming, Budgeting, and Execution (PPBE) Reform Commission has proposed sweeping changes to the defense budget process to allow for more flexibility in execution.  Increasingly, the AAF is being implemented using multiple award ID/IQ contracts with many qualified vendors delivering in MOSA.  In short, the agency is adopting the iPhone model.  

Policy Recommendations to Expand MOSA Use

To further accelerate and expand the adoption of MOSA within the Pentagon, several policy changes are recommended:

1. Codify and Enforce Open Systems Architecture Standards: The Under Secretary for Acquisition and Sustainment, along with the Military Departments, and Industry, could establish and enforce acceptable open systems architecture standards applicable to all Pentagon acquisitions. This should involve industry in defining and maintaining the open systems standards. The Pentagon can move from dictating standards to working with industry to define and refine.
2. Require MOSA for All Systems Entering Milestone B, the point at which a program enters the engineering and manufacturing development phase: Establish a policy that mandates the use of open systems architecture for all systems entering Milestone B or approved for Middle Tier of Acquisition, with appropriate waivers for exceptions.
3. Develop and Operate an Open Systems Test Bed: The Pentagon’s Chief Information Officer and Military Departments should develop and operate an open systems test bed to allow for the continued evolution of open systems best practices. For major programs (ACAT D), the program manager shall maintain their own test bed.
4. Expand MOSA to More Systems: The agency should expand the use of MOSA to more systems and make it a required test condition in all acquisitions. This will ensure that MOSA becomes a standard practice rather than an optional objective.
5. Incentivize Industry Participation: The agency should incentivize industry participation by valuing advanced practices like MOSA when writing proposal requests, making award selections, and issuing contracts. This will encourage industry investment in open systems architecture.

This strategy would also addresses broader public sector challenges by advocating for flexibility and rapid technological upgrades, essential for continuous improvement and cost efficiency. The Pentagon's progress in adopting MOSA, along with policy recommendations to expand its use, highlights the importance of agile and responsive systems in the public sector. By embracing open systems architecture, public sector entities can ensure that they remain adaptable to technological advancements and maintain a competitive edge.