Krauss-Maffei ML4000 Diesel Locomotive

Prototype Information

In the early 1960s, Germany’s Krauss-Maffei collaborated with the Southern Pacific and the Denver & Rio Grande Western to create a revolutionary diesel-hydraulic locomotive. Delivering 4,000 horsepower—double the output of most American diesels of the era—these locomotives promised to replace two units with a single powerhouse on mainline service. Their hydraulic transmissions aimed to simplify operations by eliminating the complexity of electrical traction motors and associated controls.

Three “Prototype” cab units with rounded noses and full carbodies were delivered to each railroad in 1961. Both railroads immediately tested the KMs under demanding conditions, often with dynamometer cars in tow. While performance was impressive, early reliability problems emerged. German engineers assisted in resolving technical issues and training crews, and over time, modifications improved operation. However, the locomotives ultimately clashed with American operational and maintenance practices. None of the six prototypes survived past the decade, leaving a brief but remarkable mark on U.S. railroading history.