Between 1954 and 1979, the Belgian State Railway received a total of 409 two-car electric multiple units which were also being called “Tweetjes”. The were built for 1,500 and 3,000 V DC and have gangway doors on the fronts to enable the passage of passengers when two or more sets are coupled together. With the AM 66 or MS 66 variant built from 1966, the vehicles have been upgraded on the inside and outside. These also have a top speed of 140 instead of 130 km/h. They were used for local and commuter service and withdrawals took place between 2013 and 2024. In their last years, they were also called “rode klassiekjes” (“red classics”). 