Shortly before the turn of the millennium, Deutsche Bahn and SNCF started a cooperation to develop a modern, single car diesel multiple unit. Partner companies were the French De Dietrich Ferroviaire and German Linke-Hofmann-Busch, both of which now belong to the French Alstom group. Thus, the resulting vehicle was subsequently added to the Alstrom Coradia family, while the “TER” stands for “Transport express régional”, which is used in France for fast regional trains. While in France they are also known by the nicknames „cucumber”, “suppository” and “sausage” because of their shape, in both countries they are usually called “whale” or “blue whale”.

The special thing about the vehicles is that the engines are located at both ends in front of the bogies in the floor and result in a massive appearance. The power is transmitted to the inner axle of the adjacent bogie via a Voith hydrodynamic transmission. This structure allows for a floor height of 55 cm in the middle part, which is positive when used at rural stations without a high platform.

The vehicles were built in both countries of origin, 40 of them in Germany. These are operated by DB Regio as class 641 and are primarily used on non-electrified branch lines. By far the most common variant is the X 73500 of the SNCF, which has a top speed of 140 km/h and of which 312 examples were built. There are also 19 X 73900s for cross-border traffic to the Saarland, which can be used in multiple traction with the German vehicles, and six units from the 2100 series of the Luxembourg CFL.

In France, the vehicles repeatedly make negative headlines because they have been involved in accidents at level crossings with barriers failing to close and in incidents when shunting. This was attributed to the fact that the vehicles often do not trigger track circuits for switching barriers or signals because they either have too few axles or, due to their low weight, do not sufficiently displace dirt on the tracks and thus prevent contact closure. As a countermeasure, they are often used in multiple, even if the number of passengers does not require this.

The Type 608 formed a series of six railcars with internal-combustion engines that were delivered by Forges Usines et Fonderies d'Haine-Saint-Pierre shortly before the Second World War. These vehicles were streamlined at both ends, intended for fast traffic without a trailer cars. They were built under license by Ganz in Budapest and offered ten seats in second class and 54 in third class. Both axles of each bogie were driven by an 500 hp eight-cylinder diesel engine via mechanical transmission. 

The six railcars were preceded by a Type 607 prototype that had been delivered in 1936. The Type 608 series vehicles were ordered together with the two-car type 553 railcars and delivered in 1939. They achieved a speed of up to 126 km/h in test drives, but were limited to 85 km/h in service. In contrast to other Belgian railcars, some of them survived the Second World War. It is thanks to this fact that the 608.05 can be visited in the railway museum in Treignes after a refurbishment and is therefore one of only two pre-war Belgian railcars that are still preserved today.

In order to replace the passenger transport capacity on branch lines that was lost during the Second World War, the Belgian state railways procured four-axle diesel railcars of the types 602 and 603 from 1954. A diesel engine from Carels with an output of 400 hp was used as the power plant. The vehicles stood on two bogies, only one of which was driven on the inner axle. This limited their field of application to routes in the lowlands. The differences between the two series were limited to the design of the interior. While the Type 602 also had a first-class compartment and a luggage compartment, the Type 603 only had second-class seats.

The order included six Type 602s and 30 Type 603s. The former served as a feeder to Brussels Airport, while the others served on secondary routes. In addition to the motor cars, trailers were also ordered, which were designated as Type 732 and 734 and had two or four axles.

Types 602 and 603 were later renamed MW 42 and MW 43. After the feeder to Brussels Airport was electrified, the MW 42 were converted into MW 43. As vehicles got older, some vehicles were fitted with General Motors two-stroke diesel engines. This resulted in the MW 44 on the one hand, which was given an engine consisting of two combined four-cylinders and still only driving one axle. In addition, the MW 45 was created, which received two individual six-cylinder engines, each with 165 hp, each driving one axle of each bogie. Other vehicles were converted into railway service vehicles in the 1980s. The last remotorized vehicles were in service until 2002 and were then replaced by the MW 41.

A total of 60 class M 296.1 and M 296.2 motor cars were built for the operation of important fast and express trains on non-electrified lines. The trains also included the “Vindobona” Berlin-Prague-Vienna. The vehicles are rounded at both ends, both of which have a driver's cab but a gangway only on one side. Trains were made up of two motor cars and four trailers. A 588 kW engine is located in the car body in a separate engine compartment. From 1997, 50 vehicles were converted to the class 854, receiving a new Caterpillar engine with the same power and a more modern passenger compartment.