The E 21 51 was one of the electric locomotives with single-axle drive procured at the end of the 1920s, which was assigned to the same series due to the structural similarity with the E 21 01 and 02. In contrast to these, however, it was built by Linke-Hoffmann-Busch and Bergmann and differed significantly from its sisters in terms of appearance and, above all, technical details.
Like these, it also had a 2-D-1 wheel arrangement, two small motors per powered axle and a top speed of 110 km/h, but these were the only similarities. Their power was chosen to be as high as the four driving axles would allow. At 1,400 mm, the diameter of the driving wheels was 350 mm smaller than on the E 210, which was compensated for by a higher gear ratio. The car body was constructed symmetrically and was flush with the driver's cab at both ends. Compared to other electric locomotives of the time, the fronts were slightly rounded to create less drag. In contrast to the power transmission, this feature was adopted in a similar form in later locomotives such as the E 18 and E 19 and also in the new locomotives after the war.
The axles were initially driven via a reduction gearbox, which was not particularly convincing in terms of smooth running. After a short time, teeth broke and spokes cracked, which is why a new power transmission via hollow shaft was installed. This also proved its worth, but the decision had already been made in favor of the helical-spring gear at that time.
Like the two examples of the E 210, the E 21 51 was used in the Giant Mountains and was rescued to Central Germany in the last months of the war. In the end, it too had to be handed over to the Soviet Union and returned to the GDR at the same time as the others. However, it was parked without being refurbished and finally retired and scrapped together with its sisters.