Based on the unit cars EW1 with bellows and a driver's cab of the ABDe4/8 design, six control cars Bt were delivered to BLS by the Swiss Wagon Factory Schlieren in 1963. In 1970, three more of these control cars, based on the modernized EW1 with rubber bumpers and an extended car body, were delivered to BLS. The control cars were used, among other things, in shuttle trains. From 2005, four converted control cars with the new numbers BDt 946-949 were in service with car trains, and the Bt 951-953 operated modernized with external swinging doors in the shuttle trains.