Class 503

The Class 503 was a third rail DC (650v) EMU used on the Wirral and Mersey lines. The class was built in 2 batches, the first 19 3-car sets built in 1938 for the LMS and a near identical second batch of 24 sets for British Railways in 1956-7 [1]. The Class 503s were advanced for their day with air-operated sliding doors and a high power to weight ratio thanks to the construction methods used which employed light alloys and avoided heavy frames [2].

Information
Number built: 129 cars (43 3-car sets)
Built: 1938, 1956-7
Builder: Metro-Cammell / Birmingham Railway Carriage & Wagon Company
Engine: 4 BTH traction motors (750v DC third rail)
Power: 540 hp (403 kW)
Formation: (Original) Driving Motor Brake Standard (DMBS)+
Trailer Composite (TC)+Driving Trailer Standard (DTS)
(Modified) DMBS+Trailer Standard (TS)+DTS

In the 1970s the stock was modified to have central end doors to comply with Department of Transport regulations for stock which operates in single track tunnels (to allow for the exiting of passengers in an emergency if the side doors cannot be used) [3]. They also had their first class provision removed to become fully standard class.

After a long career the Class 503 was finally withdrawn in 1985 when they were replaced by the 507s and 508s though one set was preserved and kept for special services until 1988. The preserved set is now at the Electric Railway Museum and was from the 1938 Stock batch, it is one of only two pre-war EMUs still in existence in it's original condition.
DMBS 28690 at the Electric Railway Museum

The preserved set wears LMS maroon livery

[1] Colin J. Marsden, DMU and EMU Recognition Guide (Ian Allan, 2013) p, 381
[2] R.L. Vickers, EC Electric Trains and Locomotives in the British Isles (David & Charles, 1986) p. 74
[3] Brian Haresnape & Alec Swain, Third Rail DC Electric Multiple Units (Ian Allan, 1989) p. 28