The Southern Railway gave the designation CW to the fleet of AC electric multiple unit

Electric multiple unit

An electric multiple unit or EMU is a multiple unit train consisting of self-propelled carriages, using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a number of the carriages...

s used on the lines to Coulsdon

Coulsdon

Coulsdon is a town on the southernmost boundary of the London Borough of Croydon. It is surrounded by the Metropolitan Green Belt of the Farthing Down, Coulsdon Common and Kenley Common...

 and Wallington

Wallington, London

Wallington is a town in the London Borough of Sutton situated south south-west of Charing Cross. Prior to the merger of the Municipal Borough of Beddington and Wallington into the London Borough of Sutton, it was part of the county of Surrey.- History :...

. They were planned by the London, Brighton and South Coast Railway

London, Brighton and South Coast Railway

The London, Brighton and South Coast Railway was a railway company in the United Kingdom from 1846 to 1922. Its territory formed a rough triangle, with London at its apex, practically the whole coastline of Sussex as its base, and a large part of Surrey...

 but were delayed by the World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 and the grouping

Railways Act 1921

The Railways Act 1921, also known as the Grouping Act, was an enactment by the British government of David Lloyd George intended to stem the losses being made by many of the country's 120 railway companies, move the railways away from internal competition, and to retain some of the benefits which...

 and were introduced by the Southern Railway.

Construction

The CW (Coulsdon and Wallington stock) units were built in 1923–1924, as the last electric train stock for use on the LBSCR

London, Brighton and South Coast Railway

The London, Brighton and South Coast Railway was a railway company in the United Kingdom from 1846 to 1922. Its territory formed a rough triangle, with London at its apex, practically the whole coastline of Sussex as its base, and a large part of Surrey...

 AC overhead electrified lines in South London. This stock comprised some hundred carriages, which were used in five car formations: Driving Trailer Third (DTT) + Driving Trailer Composite (DTC) + Motor Luggage Van (MLV) + Trailer Composite (TC) + Driving Trailer Third (DTT).

The stock, built by the Metropolitan Carriage, Wagon and Finance Company at Birmingham

Birmingham

Birmingham is a city and metropolitan borough in the West Midlands of England. It is the most populous British city outside the capital London, with a population of 1,036,900 , and lies at the heart of the West Midlands conurbation, the second most populous urban area in the United Kingdom with a...

, was as follows:

• 21 Motor Luggage Vans
• 60 Driving Trailers
• 20 Trailers

The Motor Luggage Vans (nicknamed "Milk Vans") each had four 250 hp GEC traction motors.

After the replacement of the AC overhead equipment by the 660 V DC third rail system adopted as standard by the SR, the carriages that formed these units were rebuilt accordingly, the Motor Luggage Vans becoming bogie goods train brake van

Brake van

Brake van and guard's van are terms used mainly in the UK, Australia and India for a railway vehicle equipped with a hand brake which can be applied by the guard...

s.