Being derived from
the Class 59 introduced by Foster Yeoman the Class 66 is a different locomotive.
It is a modern reliable replacement for elderly type 3, 4 and 5 locomotives for
medium weight faster speed freight services. The major differences from the
class 59 are the use of a GM type 710 prime mover, a self steering bogie,
revised side grille layout, smaller silencer, and the front headlight mounted
centrally above the windscreen.