Immersive simulators are needed for substantive joint warfighter training, yet the policies and practices which can help ascertain the accuracy and credibility of these complex systems are not well developed. This paper uses an ongoing effort by Air Combat Command to modify its simulator accreditation process for fighter, bomber, and C2ISR simulators as an example of the challenges in developing appropriate validation and accreditation policies for warfighter training. The paper will review current verification, validation, and accreditation (VV&A) policies and practices in the academic, Department of Defense, and Federal Aviation Agency domains as well as the Air Force simulation certification program. While necessary, these policies and practices are not sufficient for judging the credibility of flight simulators when the purpose of the simulator training is expanded to mission-level knowledge and skills. By focusing on the purpose of DMO simulators as expressed in the concepts of immersiveness, instructional integration, and interoperability, we can collect more evidence for accreditation decisions. The paper concludes with recommendations on areas of further research and policy refinements.