This paper will present information on an Interdisciplinary Systems Definition Model (ISDM) for training design and developments which is implemented during the military acquisition process, and which utilizes a diverse range of technical skills and disciplines. The central theme of the model emphasizes the need for individual technical disciplines to coordinate not only products but processes which may affect an adjacent discipline's methodology. The focus of the model is the definition and development of those aspects to be trained which address the functional and operational aspects of the system. Functional aspects in this context deal with the skills required to place the system into a state of functioning, or simply, the man-machine-interface. Operational aspects refer to activities performed by the operator(s) in response to the changing tactical environment, including coordination and communication with the supported echelon of deployment. In addition, this paper provides information on the systems engineering approach used to define doctrinal deployment and tactical applications of a system with no type classified predecessor or similar system in the field. The model will show how the disciplines of Mission Analysis, Human Factors Engineering, and Training have been brought together to define user applications. In this paper, these factors are considered in the context of the Human Factors, Manpower, Personnel, and Training (HMPT) model which preceeded the current MANPRINT model. This paper will describe how the variables of the battlefield environment, threat, and taskings affect the hardware, software, soldiers, and procedures which determine the overall contribution of the system to force effectiveness. As an example, this paper will show how the model has been applied to the Joint Surveillance Target Attack Radar System (Joint STARS), an evolving system in the Military Acquisition Process. By utilizing the skills of mission analyst, human factors engineer, and training developer, concerns related to work station layout, workload, crew size, sensor performance, and training developments have been addressed during the validation and full scale engineering development stages of the acquisition cycle for Joint STARS. Finally, this paper will show examples of how the inter-disciplinary approach was applied to system and personnel issues which affected software design, operational concepts, and training.