Having succesfully operated diesel-electric traction since 1935 with it's Lyntog or 'Lightning' DMU sets; the Danish State Railways (DSB) in 1954 sought to offset main line steam by introducing diesel electric traction for heavy haulage. At this early stage in the developement of diesel electric locomotives, the DSB sensibly ordered 5 units from the most experienced manufacturer of the time, General Motors - Electro Motive Division.
Built by Nydquist och Holm AB or NOHAB in Sweden, under license from GM-EMD, and powered by EMD's 16 cylinder 567 cid prime mover; the prototype 'Mv' class were basically a 1700HP US F-type cab unit with a second driving cab at the B or No.2 end. The most notable departure from the otherwise classic American styling was the provision of suitable screw couplers and buffers. A six wheel truck based on that of the EMD 'E unit' with an A1A-A1A wheel arrangement kept axle loads to a level acceptable for European permanent way,
So impressed was the DSB that a production run of 54 virtually identical units with slightly uprated 1950HP engines was delivered, and designated class 'My'; followed by a further delivery of 45 1425HP units classified 'Mx'.