Abstract: Systems, apparatuses and methods (“utilities”) for use in “internally” cooling the compressor of a gas turbine engine so as to approximate isothermal compression and thereby increase the power and/or efficiency of the engine. In one arrangement, a “cooling jacket” or heat exchanger having coolant circulating or passing therethrough may be mounted around an outer surface of the compressor to absorb heat or thermal energy generated from the compressor. In another arrangement, the stator blades of the compressor may include passages through which a coolant may be circulated or passed to absorb heat from air passing through the compressor.