|name = LNWR electric units
(LMS 1927 compartment stock) |image = LNWR EMU.JPG |imagesize = 300px |caption = LNWR EMU Motor Car at National Railway Museum, York |background = #012545 |Manufacturer = Metropolitan-Cammell |Operator = LMS and British Railways |Formation = power car + trailer + driving trailer |Built = |InService = 1927-1960 |Weight = |CarLength = |CarWidth = |CarHeight = |Capacity = |MaxSpeed = |Power = 4 x 280 hp traction motors
total 1,120 hp (836 kW} |Gauge = standard gauge |Voltage = 630 V DC third and fourth rail }} During 1909-1922, the London and North Western Railway embarked on a large-scale project to electrify their whole London inner-suburban network, encompassing the lines from London Euston to Watford and the North London Railway from London Broad Street to Richmond. This also included branch lines such as Watford to Croxley Green (where a depot was built to house the electric units), and links to what was to become the London Underground network. For this reason, the lines were electrified using the fourth rail 630V DC system, the electricity being generated at the LNWR's own power station in Stonebridge Park. The first electric passenger trains ran in 1914, limited to the West London Line route (Willesden to Earls Court), and full services over the whole network did not commence until 1922, work having been delayed by the First World War. The London, Midland and Scottish Railway extended the network in 1927 by electrifying the branch to Rickmansworth.
The units were delivered in three batches. The first batch, introduced in 1914, was fitted with electrical equipment from Siemens of Germany. Due to the War, the following two batches, introduced in 1915 and 1921, used equipment from Oerlikon of Switzerland.
In 1927, the LMS ordered a further batch of units from Metropolitan-Cammell to cover additional passenger services. These were broadly similar to the earlier units, but this time were fitted with more powerful Metropolitan Vickers (owned by GEC) electrical equipment. Also, the passenger accommodation was in compartments.
The Oerlikon and GEC stock survived in service in North London through to the late 1950s and early 1960s respectively, when they were replaced by the new Class 501 units. Only one car survives, Oerlikon-equipped DMBT number 28249, at the National Railway Museum, York.