A general, dimensionless formulation of the thermodynamic, heat transfer, and fluid-dynamic processes in a cooled gas turbine is used to construct a compact, flexible, interactive system-analysis program. A variety of multishaft systems using surface or evaporative intercoolers, surface recuperators, or rotary regenerators, and incorporating gas turbine reheat combustors, can be analyzed. Different types of turbine cooling methods at various levels of technology parameters, including thermal barrier coatings, may be represented. The system configuration is flexible, allowing the number of turbine stages, shaft/spool arrangement, number and selection of coolant bleed points, and coolant routing scheme to be varied at will. Interactive iterations between system thermodynamic performance and simplified quasi-three-dimensional models of the turbine stages allow exploration of realistic turbine-design opportunities within the system/thermodynamic parameter space. The code performs exergy-balance analysis to break down and trace system inefficiencies to their source components and source processes within the components, thereby providing insight into the interactions between the components and the system optimization tradeoffs.