the british rail class 45 also known as the sulzer type 4 diesel locomotives were built by british rail at their derby and crewe works between 1960 and 1962. they were the successors to the class 44 locomotives. when initially put into service the locomotives were fitted with multi-unit working and steam heating boilers for passenger service. in the early 1970s fifty were fitted with electric train supply in place of their steam heating boilers, and assigned to work services on the midland main line from london st pancras to nottingham, derby and sheffield. all were withdrawn from service by 1989.