Diesel locomotive were classified as DET 1 and DET 2 (). Due to shortage of petrol products during World War I, they remained unused for regular service in Germany. In 1922, they were sold to Swiss Compagnie du Chemin de fer Régional du Val-de-Travers (), where they were used in regular service up to the electrification of the line in 1944. Afterwards, the company kept them in service as boosters till 1965. Fiat claims a first Italian diesel–electric locomotive built in 1922, but little detail is available. A Fiat-TIBB diesel–locomotive "A", of 440CV, is reported to have entered service on the Ferrovie
Diesel locomotive deliver 1,200 volts (earlier traction "generators", DC to DC, had the capability to deliver only 600 volts). This improvement was accomplished largely through improvements in silicon diode technology. With the capability to deliver 1,200 volts to the traction motors, the necessity for "transition" was eliminated. A common option on diesel–electric locomotives is dynamic (rheostatic) braking. Dynamic braking takes advantage of the fact that the traction motor armatures are always rotating when the locomotive is in motion and that a motor can be made to act as a generator by separately exciting the field winding. When dynamic braking is utilized, the