Diesel locomotive Diesel–hydraulic locomotives have a smaller market share than those with diesel electric transmission - the main worldwide user of main-line hydraulic transmissions was the Federal Republic of Germany, with designs including the 1950s DB class V 200, and the 1960 and 1970s DB Class V 160 family. British Rail introduced a number of diesel hydraulic designs during it 1955 Modernisation Plan, initially license built versions of German designs (see ). In Spain RENFE used high power to weight ratio twin engined German designs to haul high speed trains from the 1960s to 1990s. (see RENFE Classes 340, 350, 352, 353,
Diesel locomotive accounted for 25% of the initial purchase price. Spare parts were cast from wooden masters for specific locomotives. The sheer number of unique steam locomotives meant that there was no feasible way for spare-part inventories to be maintained. With diesel locomotives spare parts could be mass-produced and held in stock ready for use and many parts and sub-assemblies could be standardized across an operator's fleet using different models of locomotive from the same builder. Modern diesel locomotives are designed to allow the power assemblies the be replaced, which greatly reduces the time that a locomotive is out of revenue-generating service