In 1954 the route south of Frankfurt was extended to Stuttgart and the Merkur became known for its long non-stop stages with steam locomotives.

In order to connect the two capitals Bonn and Copenhagen the Schwabenpfeil was withdrawn and the Merkur used its route and slot south of Hamburg.

The longer stop at Rødby Færge was caused by customs inspection and not meant to let passengers leave or board the train.

[5] Differences between Danish and German train operation caused some technical problems with heating and airconditioning.

The electric power needed for the airconditioning couldn't be provided by the Danish locomotives so the batteries of the coaches had to be loaded during the crossing of the Fehmarn between Puttgarden and Rødby Færge.

In 1991 it was decided to name the EuroCities after famous Danes and Germans, so the Merkur was replaced by the EC Karen Blixen.