After the Second World War, the Belgian State Railways were looking for electric locomotives suitable for series production. On the one hand, the Type 101 was procured, which was based on series models already used in France, and the Type 121, which was developed in Switzerland and built in Belgium with some components from Switzerland. On the other hand, three independent locomotives were developed and built by the Belgian company Baume & Marpent. These were designated Type 120 and were used in regular service from 1950.

It was a contemporary design with a cuboid but slightly rounded body, four individually powered axles and no carrying axles. These were designed for the 3,000 volt DC system used in Belgium, which had been in place since 1935 and would expand in the post-war period. The produced quantity stagnated at three, these were delivered in two shades of green and later got yellow stripes on the fronts to increase visibility. The locomotives became the HLE 20 in 1971 and just two years later they were again redesignated the HLE 28 in favor of a new class. They spent their final years shunting empty passenger trains for Brussels Midi station and were retired by 1996. Today the number 28 is used by a variant of the Bombardier TRAXX.