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.

The final set was used on special Merseyrail services until 1988; it was preserved and kept at the Electric Railway Museum near Coventry, until it moved on to the Locomotive Storage Ltd warehouse at Margate.

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.

Significant points of similarity can be seen between the Class 503 and the London Underground O and P Stock, produced shortly beforehand by Birmingham RC&W.

A known feature of the Ian Allan ABC rolling stock books for many years was that the destroyed cars continued to be listed, incorrectly, until well into the 1960s and after the replacements had been built.

[23] Careful attention allowed them to remain in good condition right up to their final withdrawal in 1985, unlike some other units elsewhere in the country at this time.

[citation needed] Every four years, major overhauls, including full repaints, were conducted at Horwich Works,[24] near Bolton.

Along with other North-West EMUs, a set would be formed up at Birkenhead North with a match wagon and hauled by locomotive to Horwich.

[citation needed] For much of the trains' life, effort was put into deciding whether to leave the off-peak formations as 6-car on any day.

For instance, during Christmas shopping weeks, or fine Summer Sundays, when the network used to handle much additional traffic from Liverpool and Birkenhead, to the seaside town termini of New Brighton and West Kirby.

[26] By the early 1970s, the livery was all-over Rail Blue, with the cab ends repainted as full yellow.

[31][36] The remainder were scrapped at Alexandra Dock, BREL Horwich and also in Northwich, mainly under contract to Vic Berry, TW Ward and HP Cartwright.

[citation needed] Until 2024, the unit was also one of the only two pre-war main line EMUs in existence which are still in original formation, the other being the 2-BIL belonging to the National Railway Museum.

During this period, the set was used for the opening of the electrified line between Rock Ferry and Hooton on 30 September 1985 and for special services during Christmas 1985.

After transport of the Driving Trailer coach from Birkenhead, the entire unit was correctly reformed at the Coventry museum in October 2010, for the first time in over 20 years The Driving Motor coach (DMBS) interior was open to the public during museum open days.