In 1964, Switzerland planned a national exhibition (Expo '64) in Lausanne. This raised a unique challenge for the Swiss Federal Railways (the SBB) that had to secure the transport of visitors from all over Switzerland to Lausanne (at the time not so many people owned a car and other modes of transport such as buses were not yet available to such an extent as it is the case today). But all modern locomotives were used in regular service and only old locomotives were available for the necessary extra trains needed to get people to and from the exhibition.

This was far from ideal and it became obvious new vehicles had to be purchased. At first, the SBB looked to buy new locomotives from existing series. The Re 4/4 and Ae 6/6 were available at the time but neither proved to be a viable solution, either for logistic reasons or performance issues. It also soon became apparent that the trains had to operate as commuter trains (very flexible and ready for use in a short timeframe) so, despite the bad experiences with the RFe 4/4, the railcars seemed to be the solution. And the success of the Ce 4/4 railcars of the BLS, offering high performance and thus the desired traction, further comforted the SBB in their choice.

The specifications for the new railcar were based on the Ce 4/4 of the BLS:
- doors over bogies;
- one pantograph (since the introduction of the double abrasive strips, a second pantograph was not considered necessary);
- inclined fronts.

The specifications also required the following:
- the railcars should be used both in regional and express services;
- they should be able to replace the Ae 3/5 and Ae 3/6 locomotives;
- the power should amount to 1988 kW or 2720 hp (higher compared with the BLS Ce 4/4 but also the SBB Re 4/4 locomotives and their 2450 hp);
- top speed of 125 km/h;
- regenerative braking;
- multiple-unit train control.

The units had to be available for testing purposes a reasonable time ahead of the exhibition and also be conceived for the long run, not only for the needs of the exhibition.

The mechanical construction of the vehicles was entrusted with the Schweizerische Industrie Gesellschaft (SIG) and Schweizerische Wagons- und Aufzügefabrik Schlieren (SWS) while the electrical equipment came from Brown, Boveri & Cie (BBC) and from Maschinenfabrik Oerlikon (MFO).