The introduction into service of the Advanced Passenger Train was to be a three-stage project. Phase 1, the development of an experimental APT (APT-E), was completed. This used a gas turbine-electric locomotive, the only multiple unit so powered that was used by British Rail. It was formed of two power cars (numbers PC1 and PC2), initially with nothing between them and later, two trailer cars (TC1 and TC2). The cars were made of aluminium to reduce the weight of the unit and were articulated. The gas turbine was dropped from development, due to excessive noise and the high fuel costs of the late 1970s. The APT-E first ran on 25 July 1971. The train drivers' union, ASLEF, black-listed the train due to its use of a single driver. The train was moved to Derby (with the aid of a locomotive inspector). This triggered a one-day strike by ASLEF that cost BR more than the research budget for the entire year.