The subject of this paper is the design and operational characteristics of a 43,000-shp combined gas turbine and steam turbine marine powerplant, known as COGAS. Based upon the “second generation technology” FT4C-2 marine gas turbine, the combined cycle fuel rate is 0.363 lb/shp-hr which represents a thermal efficiency of 41 percent. It is the intent of this paper to show that this low fuel rate design can be achieved with simplicity, operational flexibility, and minimum environmental effect.