Dieselisation
Dieselisation took place largely because of the tremendous reduction in operating costs it allowed. Steam locomotives require large pools of labour to clean, load, maintain and run. They also require extensive service, coaling and watering facilities. This was their biggest inferior measure as compared to the diesel locomotive in the number of ton-miles or passenger traffic miles either could run. Diesels could and did have a significantly higher initial price per unit-horsepower delivered. However, their far greater range between fueling stops, the absence of water stops, and the much higher unit availability between inspection repair and maintenance stops, were far better than steam. Diesels simply required significantly less time and labour to operate and maintain. Diesel power was also more scalable to power requirements, owing to the control systems that allowed multiple units to be controlled by one operator. "Double header" steam power required a crew for each locomotive. Initially, diesel locomotives were less powerful than the typical steam locomotives. Between the late 1930s and the late 1950s the power available with diesel locomotive engines roughly doubled, although the most powerful steam locomotives ever built still exceeded the power of the most powerful diesel locomotives from the late Twentieth Century.
Dieselisation
Dieselization got a boost in the early 1930s from three factors: the development by General Motors and its Winton Engine Corporation subsidiary of diesel engines with vastly improved power-to-weight ratios and output flexibility; the desire of railways to find more cost-efficient locomotion for passenger service at the height of the Great Depression; and design innovations in rail equipment that reduced weight, making the contemporary diesel engines, which were low-powered by today's standards, viable for mainline passenger service. The mid-1930s saw the introduction of lightweight diesel-powered streamlined trainsets such as the Burlington Route's "Zephyrs" and Union Pacific's M-1000x "City" trains, which were diesel's first assault against the dominance of steam in mainline passenger service. During the second half of the decade, diesel locomotives with sufficient power for full-size passenger trains were developed and put into regular production. Improved GM diesel engines in 1938 increased power and reliability. Dieselization of passenger service gained momentum as the decade drew to a close and the first model of mainline diesel freight locomotive was on the market in 1940. Dieselization was especially attractive to western railroads, for whom the watering requirements of steam locomotives were a problem in vast stretches of the western interior. Coal-country railroads were generally reluctant to embrace diesel, a competitor to one of their main hauling markets, well into the 1940s.