The 4FFFFF4l37i Class is a class of steam turbines locomotives designed by Conan Diedrich at the Eastern & Atlantic's Charlotte Works.
Steam turbine technology was very popular after World War II. Many railroads, including the E&A, investigated this technology, and after many trials with experimental locomotives, the 4FFFFF4l37i Class was finally designed.
The 4FFFFF4l37i Class was a very large piece of machinery, but represented a triumph in American steam turbine technology. Unlike other American turbines, the 4FFFFF4l37i Class exhausted into a near-vacuum generated by the condensor carried in the large tender of the locomotive. This improved efficiency substationally. The locomotive had some troubles with coal-dust and water short-circuited the drive motors, but these problems were ironed out with heavy testing.
The locomotive did beat some conventional locomotives in terms of efficiency, and many diesel locomotives as well. The locomotive had a Westinghouse turbine which drove 6 generators, which collectively drove the 12 traction motors.
The locomotive proved to be a success once the kinks had been ironed out, and was put to work on the Eastern & Atlantic's kick freight trains, which made good use of the turbine's efficiency at full load. 10 of these locomotives were built from 1956-1958.