This paper describes a study conducted during the design phase of a weapons system trainer (WST) for the U.S. Air Force Special Operations Aircrew Training System. The purpose of the study was to identify key instructor requirements of the instructor operating station (IOS) for the WST. During the pre-design and early design phases, an analysis of existing IOS stations was conducted to determine their strengths and weaknesses. The analysis considered instructor tasking requirements, along with task saturation points in the mission training from the perspectives of both student crew members and instructors. The results indicated that many required human factors and instructional design features were not effectively built into many of the existing stations. Several factors also complicated the IOS for this system. The requirement for instructors to have both over-the-shoulder and IOS access to students, combined with the multiple crew positions involved, created complex design problems to solve. Following the analysis of existing systems, a study was developed to determine the critical elements of instructor interface both to the IOS and to the student during both crew station (individual) and weapons system (crew) training exercises. Mission scenarios were designed for use in this study which paralleled real-world situations. The segments of the missions most subject to task saturation for instructors and students were identified. The scenarios were then run under controlled, simulated conditions. The scenarios were videotaped for analysis and systematic debriefing sessions were held following each scenario. The data was analyzed by instructor and mission tasking requirements. Study results were used to define specific design requirements which would meet the instructional needs of the students and the tasking and operational requirements of the instructor. Refinements to the design of the instructor operating stations were made to maximize both the station's human factor capabilities and the instructor-student interactions. General design guidelines are provided for future research in this area.