The DoD's digital transformation is advancing with domain specific modeling languages (DSMLs) for precise design specifications, which are better suited than general purpose modeling languages, like SysML, when implementing complex designs. Tangram Flex has successfully used Retrieval-Augmented Generation (RAG) with large language models (LLMs) to generate DSML code quickly and accurately. Experiments showed significant time savings when using LLMs, reducing development from months to weeks. Additional benefits include easier verification and a reduced learning curve for new users. LLMs thus enhance rapid, confident development of DSMLs, easing adoption for systems and software engineers.