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 as EMD's main competitor in the early 1960s, eventually taking the top position in the locomotive market from EMD. Early diesel–electric locomotives in the United States used direct current (DC) traction motors, but alternating current (AC) motors came into widespread use in the 1990s, starting with the Electro-Motive SD70MAC in 1993 and followed by the General Electric's AC4400CW in 1994 and AC6000CW in 1995. In 1914, world's first functional diesel–electric railcars were produced for the "Königlich-Sächsische Staatseisenbahnen" (Royal Saxon State Railways) by Waggonfabrik Rastatt with electric equipment from Brown, Boveri & Cie and diesel engines from Swiss Sulzer AG. They