The British Rail Class 502 was a type of electric multiple unit originally built by the London Midland and Scottish Railway at their Derby Works. Introduced in 1940 and withdrawn by 1980, they spent the whole of their working lives on the electrified railway lines of north Liverpool.
The trains were designed to replace older electric trains built by the Lancashire and Yorkshire Railway on the lines from Liverpool Exchange station to Southport and Ormskirk. These lines were electrified with a Direct Current (DC) third rail. The Class 502s entered service between 1940 and 1943. They were DC-only and operated as both 3-car and 2-car sets, which could be coupled together to form 5-car or 6-car sets for use on the busier services.