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
ČKD T-669 diesel locomotive ČKD T-669 diesel locomotive T-669.0 (770) class diesel locomotives, built by ČKD are six-axle, with two bogies. The wheel pairs are set in radius arms and have a simple coil spring suspension. The body is mounted on the frame with eight anchors. The locomotive is a hood unit type with an internal, eccentrically-positioned operator's cab. Located underneath the front hood is the traction assembly – a K 6 S 310 DR diesel engine and a TD 802 traction generator – and auxiliary machinery powered by the diesel engine via a hydrodynamic transmission. Chillers and ventilators are located here as well.