High Quality Content by WIKIPEDIA articles! The Advanced Passenger Train (APT) was an experimental tilting high speed train developed by British Rail during the 1970s and early 1980s. The introduction into service of the Advanced Passenger Train was to be a three-stage project. Phase 1, the development of an experimental APT, the APT-E, was completed. Phase 2, the introduction of three prototype trains, known as the APT-P, into revenue service on the Glasgow-London route, enjoyed only limited service due to bad publicity. Phase 3, the introduction of the Squadron fleet designated APT-S, did not occur. The knowledge and experience gained enabled the construction of other high speed trains, including tilting derivatives.