British Rail Class 503 passenger trains were electric multiple units. They were introduced in two batches. The first were in 1938, by the London, Midland and Scottish Railway (LMS) with a further batch (built to a similar design) in 1956 by the then nationalised British Railways (BR). When introduced by the LMS, they were officially known as Class AM3. They were designed for, and operated on, the Wirral & Mersey lines from Liverpool to West Kirby, New Brighton, and Rock Ferry. There were few places on their network of closely spaced stations to attain their maximum speed, except for the open section between Moreton and Meols. All but one set were withdrawn and scrapped by 1985. The final set was used on special Merseyrail services until 1988, and this preserved set was kept at the Electric Railway Museum near Coventry until moved to the Locomotive Storage Ltd warehouse at Margate. Overview When introduced by the LMS, the class was officially known as Class AM3. The two batches were almost identical, a difference being that the 1938 stock had passenger door-open buttons mounted on the doorleaf itself, whereas on the 1956 the buttons were on the bodyside next to the door. Motor units could be identified from the driving trailers by the ventilation louvres in the bodyside near the car ends which led to ducting down to the motors. Originally, these trains featured a flat front. Emergency end doors were added, in 1972, as part of a Department of Transport directive for when working in a tunnel. The trains were fitted with four position marker lights on the front, which were used throughout their life as indicators to signalmen - both top lights for Rock Ferry, both right-hand lights for West Kirby, and one top light for New Brighton. When first introduced they were seen to be of a very advanced design for a mainline railway's suburban passenger trains, featuring things such as air-operated sliding doors which were opened and closed by the guard (hitherto trains either had "slam doors" or hand-operated sliding doors). Class 503 were the first group of electric trains on the main British railway system with air-operated power doors, located at the quarter points of each coach under the control of the guard, which became a later general standard. Builders They were not built in the LMS's own workshops, but by contractors in Birmingham: Metro Cammell of