Ingersoll-Rand Number 90 Diesel Locomotive, 1926

By the 1920s steam locomotive designers were applying scientific research in areas such as thermodynamics and metallurgy to the hard-won practical know-how that had driven locomotive development throughout the nineteenth century. At the same time, breakthroughs in other areas such as electrical engineering and internal combustion power were being recognized as having likely railroad motive power applications. This locomotive represents a convergence of those technologies. Its body houses an Ingersoll-Rand Diesel engine that drives a General Electric generator, which in turn powers electric motors mounted on the axles. The flexibility and economy of Diesel locomotives ultimately drove the demise of steam locomotives in the United States, but when this locomotive was built those advantages were not yet entirely apparent.