The railway reopened post WW1 on the 9th of June 1919, work immediately starting on upgrading the power supply to the railway, with the Power Station below the Bungalow last steaming on the 3rd of September 1924, with an additional rotary converter added to replace it. In May 1935, the two converters were replaced by two Mercury Arc Rectifiers, located in the M.E.R substation at Laxey, drawing from the public supply.
After running successfully throughout the 1920s and 1930s, the line closed due to the outbreak of World War 2 on the 20th of September 1939, with the top-section overhead from the Bungalow to Summit section being removed and stored at Laxey. Reopening after the War took place on the 1st of June 1946, with a heavy renewal programme being required for both the service cars and the line, all 6 cars being tripped in stages to Derby Castle for a full overhaul and repaint. In 1950, the Air Ministry (later the Civil Aviation Authority) established a radar station on the Summit, and, due to the wiring being taken down on the top section between Bungalow and the Summit each winter, a Wickham Railcar, No.5864 was ordered in 1951, so that the radar operator could drive to and from the summit.
Despite the recording of good profit until 1952, the railway was nationalised by the Isle of Man Government on the 1st of June 1957, falling under the same board as the Manx Electric Railway.