In search of more powerful diesel locomotives, the Denver & Rio Grande Western ordered three ML 4000 from Krauss-Maffei in Germany in 1961. With hydraulic power transmission and two high-speed Maybach engines with 2,000 hp each, their basic technical concept was completely different than that of American locomotives. The advantages lay in the better power-to-weight ratio and better traction properties of the three-stage transmission. In order to cover the development costs, Southern Pacific was persuaded to order three more ML 4000.