While the Modular Open Systems Approach (MOSA) has been a requirement for major defense acquisition programs since January 2019 and other Defense Department acquisitions since January 2021, few programs are implementing the standard, according to a Government Accountability Office (GAO) official. For Pentagon systems, MOSA is to aid "iterative development" in which programs do not spend years designing systems and obligating billions at the outset of a contract to deliver specific, customized military requirements, but instead designing systems to desired…