This is a rare and historically significant technical manual titled "DIESEL-ELECTRIC LOCOMOTIVES," published by the International Textbook Company as Serial 5685, Edition 1. This document captures a pivotal moment in American railroad history, chronicling the technological transition from steam to diesel-electric power. The text provides a detailed narrative of this evolution, beginning with the monopoly of steam locomotives and the limitations of early electric systems. It specifically notes the emergence of the diesel-electric locomotive as a new competitor around 1935, marking a revolutionary shift in railroading. The manual delves into key historical milestones, including Union Pacific's early 1905 experiments with a gasoline-powered passenger car and the critical role of figures like Mr. H. L. Hamilton, founder of the Electro-Motive Corporation, in reviving gasoline-electric technology in 1922. It also references the Burlington Railroad's order of the first diesel-electric powered train following the Chicago Century of Progress exhibition, a landmark event in transportation history. The content is comprehensive, covering the development, classification, and intricate mechanics of diesel-electric locomotives. It includes detailed technical discussions on topics such as the shift from mechanical to electric drive by 1933, the engineering challenges of weight-to-power ratios, and the function of critical components like the load regulator, which is illustrated in a detailed diagram labeled "FIG. 10. LOAD REGULATOR." The manual further contains a valuable cutaway illustration, "FIG. 3. GENERAL ARRANGEMENT OF 1,000-HP SWITCHING LOCOMOTIVE," which meticulously labels internal components such as the diesel engine, main generator, traction motor blower, and control stand. Operational scenarios are also covered, including a section on using steam engines as helpers with diesel locomotives, a common practice during the transitional era. The inclusion of the original examination questions page, with a "Notice to Students," confirms this was part of a formal vocational correspondence course, likely from the International Correspondence Schools (ICS), used to train the railroad engineers and mechanics who would operate and maintain this new technology. The condition of this manual is consistent with its age and educational use. The pages are composed of a cream-colored paper that has developed a pronounced patina and shows significant age-related foxing, which appears as brown spotting, particularly along the top and bottom margins. There is also noticeable staining that resembles water marks on several pages. Despite these signs of handling and age, the paper remains intact with no major tears, and all text, technical narratives, and detailed diagrams are fully legible. The binding edge is visible, indicating it was once part of a larger bound volume or loose-leaf course set. This piece is an exceptional artifact for collectors of railroadiana, historians of industrial technology, or modelers seeking authentic period engineering details, offering a direct window into the educational materials that shaped the dieselization of America's railroads.