A modern fighter engine has stringent requirements for performance, operability, and durability. To meet these conflicting requirements and to ensure a balanced design, dynamic simulation is exercised during flow-path design, control-mode design, and development testing. This assures problem prevention and reduces development costs. This analytical process is described with the aid of "real world" examples. Representative engine models, which accurately account for off-design and dynamic effects, are used early in the design phase for judicious configuration selection and control-mode design. Favorable component matching is ensured before hardware fabrication, and thus costly mistakes are prevented. The special flow-path design considerations in fastresponse twin-spool afterburning turbofan engines are discussed. In addition to flow-path design, simulation tradeoff studies are used to optimize the control system to satisfy systems requirements. Novel control modes can be analytically evaluated across the operating spectrum and made practicable with appropriate activation criteria that are readily implemented in digital-control logic. Simulation applications during development/flight testing include calculation of hard-to-measure engine parameters using test data driven dynamic engine models, thus facilitating design verification. The described process has been successfully used and is illustrated here with its application to the F100-PW-229 (PW229).