Defense Software Acquisition Cadre Act of 2021 This bill requires the Office of the Under Secretary of Defense for Acquisition and Sustainment of the Department of Defense (DOD) to establish a group of experts on development and acquisition of software to ensure a consistent, strategic, and highly knowledgeable approach to developing and acquiring software in support of DOD Instruction 5000.02, Operation of the Adaptive Acquisition Framework (January 23, 2020).