Model-Based Systems Engineering (MBSE) is a systems engineering methodology that incorporates a set of domain models used to define, design, and document a system under development.  D2K has taken the concept further by incorporating these domain models into software in order to leverage their utility during system requirements derivation, design, analysis, test, verification and validation. Our version of this practice, known as Model Based Engineering (MBE), is consistent with the notion of the Digital Thread, where related domain models are used to achieve benefits throughout the project lifecycle. They are also useful after deployment for software maintenance and operator training.