Built between 1962 and 1968, the Class 47 Co-Co Diesel-Electric locomotive was once the most numerous class of mainline diesel in Britain with 512 examples. 310 locomotives were constructed by Brush in Loughborough, and the remaining 202 at Crewe. The locomotives were used for passenger and freight operations. Between 1998 and 2004 33 of the locomotives were converted to Class 57s by Brush Traction. The Class 57 features re-conditioned EMD engines and new traction alternators. Network Rail leased six Class 57s fitted with either tightlock couplings or Dellner couplers enabling them to be used as rescue engines for EMUs in the south of England, with the locomotives having fulfilled a similar function as Virgin Train Thunderbirds on the ECML.