>>1319721I'm not completely sure what you mean but on the ECML and GWML, the then class 253/254 diesel trainsets operated high speed services on non electrified routes, during the 1980s, the ECML was being electrified in preparation for the intercity 225 electra sets, while on the slow lines the class 101s and other slam door DMUs were being replaced by class 317s, and more recently on the GWML, amid electrification for the new IEP trains, the slow lines saw class 165/166 networker turbos being replaced by class 387 electrostars.
