Pratt &amp; Whitney GG4Pratt &amp; Whitney GG4 Pratt & Whitney GG4 The Pratt & Whitney GG4 and FT4 are related aero-derivative gas turbine engines developed from the Pratt & Whitney J75/JT4 turbojet line. They are axial twin spool turbojets with a can-annular type combustion element, typically operated as turboshaft engines. In this configuration the gas generator provides the expanding gases to drive a power or “Free Turbine”. This turbine is then used to drive electrical generators, mechanical pumps or propellers for marine applications. The GG4 is a self-contained; self-regulating; remote operated; quick responding; peaking power generating set, that can also be used for electric propulsion  in naval vessels and to drive gas compressors for water and gas pipelines. It was introduced in the 1960s with approximately 1,300 units in operation at its peak. Many units are still in operation globally today. The typical output of a single engine ranges from 16 to 30 MW depending on conditions and configuration. Engines can be combined to work in conjunction with up to 8 other engines for more efficient power generation. They may also be operated as a combined cycle unit in combination with a condensate boiler in order to increase efficiency. Pratt & Whitney GG4 The Pratt & Whitney