Watford DC line

The Watford DC line is a suburban railway line in Greater London and Hertfordshire running between London Euston and Watford Junction. The line is shared by services on London Underground's above-ground section of the Bakerloo line between Harrow & Wealdstone and Queen's Park, and London Overground's Lioness line which runs over its entire length.

The line runs beside the West Coast Main Line (WCML) for most of its length. The rolling stock used on the line are the London Overground Class 710 "Aventras" made by Bombardier and the London Underground 1972 Stock.

The Watford New Line was opened in stages by the London and North Western Railway from 15 June 1912 as part of a wider scheme of suburban capacity improvement and electrification. Delayed by World War I, full electric service from Watford Junction to Euston commenced on 10 July 1922.

The "DC" in the title refers to line being electrified using direct current. This was done in the early twentieth century with conductor rails to be compatible with the four-rail system used by the Underground and, at the time, the North London Line; currently, the line uses a third rail system, with a fourth rail available on the section shared with the Bakerloo line. By contrast, the WCML uses overhead alternating current.

The London and North Western Railway (LNWR) drew up a plan in 1907 to widen their line between Watford and Kilburn and continue on to Euston in tube tunnel. This was superseded in 1911 by a more ambitious plan that included new lines on the surface from Watford to Chalk Farm, electrification of this and other lines and linking up with the Bakerloo line.

The Watford New Line was opened in phases. The section of double track between Willesden Junction and Harrow & Wealdstone opened on 15 June 1912 and was used for local steam train traffic. The new stations at Harlesden, Stonebridge Park, North Wembley and Kenton opened on 15 June 1912.

The section of new line between Harrow & Wealdstone and Watford High Street opened on 10 February 1913, with a new station at Headstone Lane. Local steam trains were now able to use the new line between Watford Junction and Willesden Junction. The existing station at Watford High Street received direct services to London for the first time. The opening of this section of line coincided with the beginning of service at Croxley Green and Watford West stations on the Croxley Green branch line.

Queen's Park station became the northern terminus of the Bakerloo line on 11 February 1915. The station was due to open with Kilburn Park and Warwick Avenue stations on 31 January 1915 but was delayed because of World War I.