Change at the time was fast moving, besides those in the nature of traffic carried.
The first Pilot Scheme loco delivered was in the middle of 1957. Annual totals for the 174 locos were 1957 - 21, 1958 - 82, 1959 - 68 and 1960 - 3.
By the time that delivery of the Peaks wast completed Brush were working on Falcon and BRCW were working on Lion so the 40, 44/45/46 were already redundant technology. The 47 was a more or less a hybrid of the Sulzer power unit from Lion in the Brush loco.