The original NMBS/SNCB Class 28 locomotives were produced by Baume - Marpent (nl) in 1949 and entered service in 1950.

They were built as prototypes to help SNCB develop a standard electric locomotive for future electrification projects.

They are in no way related to Type 101/Class 29 locomotives, which were an off the shelf design already in use as Class BB 300 by SNCF.

Class 121 was designed in Switzerland and used a number of existing Swiss components but they were assembled in Belgium.

The Class 28 number series has been reused for leased Bombardier TRAXX locomotives, 2801 to 2843.