After being severely damaged in a derailment near Peterborough in 1974, locomotive 47046 was selected to be a testbed for the projected Class 56, and was fitted with a 16-cylinder Ruston 16RK3CT engine rated at 3,250 bhp (2,420 kW) for assessment purposes.
 To identify it as unique, it was renumbered 47601 (at the time the number range for Class 47s only extended as far as 47555).
Later, in 1979, it was used again for the Class 58 project, fitted with a 12-cylinder Ruston engine (this time of 3,300 bhp (2,500 kW)), and renumbered 47901.
It continued with this non-standard engine fitted until its withdrawal in 1990.
After being severely damaged in a derailment near Peterborough in 1974, locomotive 47046 was selected to be a testbed for the projected Class 56, and was fitted with a 16-cylinder Ruston 16RK3CT engine rated at 3,250 bhp (2,420 kW) for assessment purposes.  To identify it as unique, it was renumbered 47601 (at the time the number range for Class 47s only extended as far as 47555). Later, in 1979, it was used again for the Class 58 project, fitted with a 12-cylinder Ruston engine (this time of 3,300 bhp (2,500 kW)), and renumbered 47901. It continued with this non-standard engine fitted until its withdrawal in 1990.
British Rail Class 47