[4] In the early 50s the DSB was starting to look for a new type of motive power that could replace steam locomotives in Denmark.

[8] To replace steam on branch lines, a similar but lighter locomotive, the class MX, was developed, incorporating a 12-cylinder 567 engine.

The others have either been scrapped or sold to diverse private operators in Norway, Germany and Sweden, who now use them on light freight duties.

[11][12] MY 1149 received a spare 645E engine (as used in class MZ, though with the turbocharger removed) after sustaining severe frost damage in the harsh winter of 1978–79.

[14] The locomotives were delivered in DSB's then-standard maroon colour, with horizontal white stripes along the mid and bottom of the sides and a yellow winged wheel at each front.

Starting in 1965, the DIN 1451 typeface was slowly introduced for the lettering, and a few locomotives were given an "economy" maroon livery without stripes during the 1970s.