Tatra developed the vehicles, also known as “tower railcars”, to transition passenger transport on branch lines and narrow-gauge railways with low passenger density from steam to internal combustion engines. Designer Hans Ledwinka's idea was to simplify operation and reduce costs with a single, elevated driver's cab. Its chassis corresponded to a two-axle goods wagon and the engine was suspended in the middle. The driver sat above the engine on a rotating chair from which he could see both directions of travel.
Most variants were powered by a petrol engine with an output of between 65 and 120 hp, which was connected to a four-speed gearbox and drove one axle. A conventional reversing gear was installed in the first variants. Later, engines with two camshafts were used, which could turn in both directions and thus made it possible to drive forwards and backwards. The tanks were arranged on the roof in front of and behind the cab. Depending on the engine power installed and the route profile, up to two specially developed trailers could be attached.
The first construction lot from 1928 included three different types. The M 120.3 series with 36 seats and an overall length of 9.20 m, which reached 55 km/h and of which a total of 27 examples were built up to 1930, was created for passenger transport on standard-gauge routes. At the same time, the M 140.1 series for express freight traffic was created, which was only 5.80 m long, was the fastest variant at 70 km/h and was only built four times. Furthermore, the M 11.0 series, which was somewhat narrower and shorter than the M 120.3 series, was built nine times for the Bosnian gauge of 760 mm.
The variants built later were all passenger railcars in standard gauge, which were between 10.53 and 10.70 m long and had a higher engine output. It all started with the M 120.4 series, of which 89 examples were built between 1930 and 1935. They initially had 100 and later 120 hp and were 60 km/h fast. A total of 63 examples of the M 130.2 series were built between 1933 and 1937 with the same dimensions and power data, but a new interior design. At the same time, the M 130.3 series was created, 30 of which had a diesel engine with initially 120 and later 125 hp and were otherwise almost identical to their sisters.
The vehicles were distributed to many branch lines within Czechoslovakia. After the annexation of the Sudentenland by Germany and World War II, some vehicles were removed from their ancestral territory. Just some of the narrow-gauge railcars of the M 11.0 series made it to Austria and later others were on Hungarian or Romanian territory. The majority of the vehicles remained in Czechoslovakia after the end of the war. With the introduction of the modern railcars of the M 131.1 series, the M 120.3 series was at first phased out by 1949. The M 120.4 series lasted the longest, the last examples of which were parked in 1965.