Embedded training is the mechanism by which training capabilities are combined with actual combat systems capabilities to provide training during routine use of the combat systems. With embedded training, effective training can be realized with a modest investment if the unique requirements for the development of embedded training are properly considered. Many elements of embedded trainers are similar to those usually considered for ground trainers while some elements may be vastly different. In an embedded trainer, the training scenario, operational requirements of the systems with their embedded simulators, the system design and integration, and the situational awareness of the student may be quite different from those of a ground trainer. Though many ground trainers have superb fidelity and realism, they cannot replace the experience gained from actual flight training. While gaining the required flight experience, operators using embedded training acquire the extra edge to maintain proficiency as they become acclimated to the multi-stress combat environment. This paper explores some of the unique requirements that have been uncovered on the On-Board Electronic Warfare Simulator (OBEWS), one of the first embedded trainers, now being test flown on an F-16. The subjects that are covered include aspects of the training requirements such as fidelity of simulation and ground requirements; system design, (i.e., can you add onto existing systems or do you need to design it in); the growth of the concurrency problem, now including the system and the aircraft; a look at integration and adaptability for designing into a pod or for internal carriage; and the environmental constraints, (e.g. how to produce the equipment to withstand the environment on the wing of a fighter).