In 1971, Deutsche Bahn (DB) commissioned the development of two prototypes of the 614 series. These diesel multiple units, specifically designed for district and regional traffic, were an evolution of the 624/634 series and featured a slightly tapered body shape to accommodate a so-called "track curve-dependent body control (GSt)." This gave the trainset its distinctive appearance. However, since the GSt ultimately proved ineffective, it was omitted from the 40 series vehicles delivered between 1973 and 1977, although the body shape remained. MAN manufactured the intermediate cars for 25 units, while the Uerdingen wagon factory produced the motor cars equipped with either a 330 kW or later a 367 kW engine. The last 15 sets (from 1975) were entirely manufactured by MAN. Although the trainsets were designed as three-part units (204 seats in second class and 2 x 12 seats in first class), they were capable of multiple traction and occasionally operated as four-part units with an additional intermediate car, especially in the early days. However, multiple traction was quite rare, and in later years, it was almost nonexistent. The first 25 units were assigned to the Bw Nürnberg depot, from where the trainsets were deployed on all non-electrified routes in Franconia and the Upper Palatinate. The typical color scheme at that time was the "Pop" livery in blood orange and pebble gray. The last 15 trains—now in the color scheme of ocean blue and ivory—were stationed at the Bw Braunschweig depot, from where they operated on routes to Paderborn, Göttingen, Münster, and Bielefeld, among others. They could also be seen at the end of their service on the Heidebahn from Buchholz via Soltau to Hanover. Most vehicles were later repainted in mint turquoise and light gray, and by the end, almost exclusively in traffic red. As part of a partial modernization, several units received a more powerful engine (448 kW).