The British RailClass 46 is a class of diesel locomotive. They were built from 1961–1963 at British Railways' Derby Works and were initially numbered D138-D193. With the arrival of TOPS computer system they were renumbered to Class 46. Fifty-six locomotives were built. The first was withdrawn in 1977 and all of them were withdrawn by 1984.
The Class 46 design was structurally the same as the earlier Class 45 build, and had the same Sulzer engine. It differed in the fitment of a Brush generator and traction motors, in place of the Crompton Parkinson equipment fitted to the Class 45.