The Z4 Class is a class of steam turbine locomotives designed by Conan Diedrich at the Eastern & Atlantic's Charlotte Works.
During the late 1950's, the Eastern & Atlantic built a series of steam turbine locomotives which were the only successful examples of such locomotives in the United States. Their success came from the combination of heavy testing and the use of individual steam nozzles to admit steam to the turbines, in a similar way to the British Turbomotive locomotive.
The Z4 Class had a 4-8-8-4 wheel arrangement; that is, it had two leading axles, followed by two articulated sets of four axles, followed by two trailing axles. The Z4 Class had a Babcock & Wilcox water tube boiler, which supplied steam to eight individual nozzles which drove the massive turbine. The turbine, in turn, drove four generators, which turned eight traction motors. The locomotive had a large coal bunker ahead of the cab, with the water tube boiler facing towards the rear of the locomotive. The turbine and generators were placed after the boiler.
The Z4 Class was designed for express freight and passenger service. The turbine's maximum allowable rpm allowed running at a maximum speed of 90 mph.
The Eastern & Atlantic's steam turbines were efficient examples of turbine technology, and proved useful in keeping time with the Eastern & Atlantic's symbol freight and crack passenger trains.