The Kwun Tong line operates over the majority of the track used by the "Modified Initial System", and can so be said to be the first MTR line to enter service. It was predated only by the suburban East Rail line, which at the time was in the process of being electrified and upgraded to a commuter service as part of the Kowloon–Canton Railway. Construction was approved in November 1975 under the administration of Governor Murray MacLehose, and service commenced on 1 October 1979. The line initially ran between Shek Kip Mei station and Kwun Tong station, and each train consisted of four cars. It was extended to the south twice: firstly to Tsim Sha Tsui on 31 December 1979, and secondly to Central station on 12 February 1980 (named "Chater" at the time), crossing Victoria Harbour through the first underwater rail tunnel in Hong Kong and completing the original Modified Initial System plan. When the Tsuen Wan line started service in May 1982, it took over the section of the Modified Initial System south of Argyle (present-day Mong Kok). At that point, Waterloo (present-day Yau Ma Tei) station became the terminus of the newly-christened Kwun Tong line (until then, the line had no official name), and both Argyle and Prince Edward stations became cross-platform interchange stations with the new line. When the Hong Kong government decided to build a second harbour crossing in 1984, it awarded a franchise for the construction of a mixed rail and road tunnel under the harbour. Consequentially, the Kwun Tong line was extended through the new tunnel on 6 August 1989 to a new terminus at Quarry Bay, a transfer station with the newly-built Island line. An intermediate station, Lam Tin, was opened on 1 October of the same year. The first derailment in MTR history (excluding ex-KCR lines) took place at Kowloon Bay station in 1994. The seventh carriage of a train pulling into the station at about 60 km/h jumped the tracks on 28 January 1994, on a section of track adjacent to the MTR headquarters building. Nobody was injured, though train services were disrupted. The incident was blamed on a bolt in the train's suspension system which had worked itself loose, causing the weight load to be concentrated on the rear wheels of the carriage. As part of a project to reduce congestion at Quarry Bay, the Kwun Tong line was briefly extended to North Point on 27 September 2001.