new underground stations at Moorfields and Liverpool Central as part of the Northern Line of the Merseyrail network. The electrification was also extended to Kirkby, on the Wigan line, to the north-east of the city and Garston, to the south-east, using Class 502s. The units struggled to cope with the challenging gradients in the new underground sections, which are as steep as 1 in 30 in places, and their reliability suffered. Depots The principal depot was in Southport, on the Preston / Manchester lines at Meols Cop. In the mid-20th century there was a triangle, and the works were situated in the middle. The Preston line closed in the mid-1960s, and the electrified lines from Southport to Meols Cop remained for a further six years, to enable the Merseyrail 502 stock to reach the depot under their own power. Meols Cop closed in 1970. Servicing was then continued at Birkenhead North depot. Hall Road also had a maintenance depot, which conducted minor repairs, and sidings to the north of station; and at the side of the depot. Stabling points were also situated outside Southport Chapel Street station and at Bank Hall, to the west of the four live running tracks. The Bank Hall stabling point fell into disuse prior to the Loop and Link extensions of the 1970s and was replaced by Kirkdale depot in 1976. Numbering British Railways numbers were: Driving Motor Brake Second, M28311M-M28369M Trailer Second, M29545M-M29594M Trailer Second (built as Trailer Composite), M29812M-M29820M Driving Trailer Composite, M29866M-M29899M Formation These formed, notionally, 34 3-car units Motor-Trailer-Driving Trailer, and 25 2-car units Motor-Trailer. The 2-car units only had a driving cab at one end and could not be operated on their own, only coupled to one of the 3-car units, which was an unusual feature of this stock. It was normal to form the main 5-car sets with the motor cars at the outer ends of the formation, and the trailer coupled to the driving trailer in the centre. The 6-car sets were formed with motor cars at the outer ends of the formation with the driving trailers coupled together in the centre. There were a number of different formations used, but 5-car sets were usual on the main Southport and Ormskirk routes, with a couple of the busiest peak trains being 6-car, formed of two three-car units coupled together. The Crossens shuttle was a 3-car unit, or a