After the DSB had already procured licensed American EMD locomotives from NoHAB in Sweden in the 1950s, another series of this type followed from 1967 with the MZ. The locomotive body and the traction motors were produced in Denmark. Like all EMD locomotives of that time, these were diesel-electric locomotives with a two-stroke diesel. With the then current sixteen cylinders of the 645 series with 3,300 hp, the first series of the MZ was already the most powerful diesel locomotive in Europe at the time it went into service. In contrast to the previous MY and MX series, all six axles were powered to transmit all the power to the rails.
The first series, which later became known as the MZ (I), was followed in 1970 by the technically almost identical MZ (II). Both were equipped with steam heating for heating passenger trains. From 1972 the third series followed, which got the twenty-cylinder known from the SD45 with here 3,900 hp. At the same time, the top speed was increased from 143 to 165 km/h. From 1977, the MZ (IV) finally followed, which had electric train heating for the first time. With these four series, a total of 61 pieces were created.
From 1978, the MZ (III) also received electric train heating with an output of up to 480 kW. The steam generators were not removed until 1985. Between 1980 and 1985, the first two series also received electric train heating. This had an output of up to 440 kW and was powered by an additional diesel engine in order not to further strain the engine output, which was lower than that of the later series. Also in the 1980s, a snow plow and radios for route radio were installed after a particularly harsh winter had revealed the weaknesses of the locomotives. After the phasing out, which started in 2000, many engines were sold to Sweden and Australia.
