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
TU2 diesel locomotive the Ways and Communications. The tests were successful, so the TU2 was taken into production. The only factory that produced the TU2 was Kaluga machine factory. The first three locomotives were tested again, in Panevėžys, (Lithuania) and Pärnu, (Estonia). During the tests, the locomotive could run as fast as . But due to the poor tracks on most of the country's narrow gauge railways, the highest allowed speed during normal operation was . TU2 diesel locomotives were produced till 1959; 281 locomotives were built. The locomotives were used on many narrow gauge railways to haul cargo as well as passenger