of a low voltage control signal. After inspection by the Board of Trade, the line was approved as fit for traffic on 3 April 1903. The last steam trains ran on Saturday 2 May and the current to the electrified rails was switched on at 3:30 am. At 4:53 am the first electric train arrived at Liverpool Central, and for the Sunday morning trains ran at 3-minute intervals without passengers. Passengers were admitted when the advertised Sunday service started at noon. The stations were cleaned, whitewashed and electrically lit. A service was provided every three minutes from Liverpool Central to Hamilton Square and journeys were faster: Central to Rock Ferry was eleven minutes, down from fifteen minutes and the Central to Birkenhead Park journey was reduced by two minutes, down to eight minutes. There was a maximum of four cars per train in 1904, which was raised to five cars in 1909. In 1923, automatic signalling was commissioned at Liverpool Central and in 1927 the island platform was widened, the work being completed in a weekend. The maximum number of cars in a train was raised to six in 1936, after the tunnels at the east end of Liverpool Central had been extended. Wirral Railway As a local railway the Mersey Railway remained independent in the 1923 grouping, although the Wirral Railway became part of the London, Midland and Scottish Railway (LMS). The Wirral had authority to electrify its lines, but had not done so, and passengers making through journeys had to change at Birkenhead Park. In 1926 discussions started on electrification and through running. The Wirral section was electrified with a DC third rail system, the Mersey Railway retaining its fourth rail but moving the positive conductor to from the running rail. The Mersey Railway electric multiple units were modified to run to the Wirral railway, and at the same time heaters and air compressors were added. In 1938 the LMS introduced new lightweight three car multiple units that were later, under British Rail, to be classified Class 502. Nationalisation and legacy In 1948, on nationalisation of the railways, the Mersey Railway became the Mersey section of the London Midland Region. In 1956 these trains were replaced by Class 503 units, similar to the LMS Class 502 design, and the fourth rail removed. The last of the American-designed cars was withdrawn a year later. A single track loop line