The first class 57 locomotives were rebuilt by Brush between 1997 and 2004 for Freightliner. Class 47s were used to supply a core bodyshell with the 47s Sulzer engine and generator being replaced by a 12 cylinder EMD 645 engine allied to a refurbished Brush alternator recovered from withdrawn class 56 locomotives. Following on from the Freightliner locomotives Virgin Trains ordered a batch of class 57 locomotives equipped with electric train supply alternators and Dellner couplings compatible with the new all-electric Pendolino trains so these could be hauled over non-electrified routes and to act as 'Thunderbird' rescue locomotives to assist and recoevr any failed units.