With numerous manufacturers being required to produce their own designs to meet the deadline, the standardisation intended in the Modernisation Plan could not be achieved. The three standard classes originally planned – and even the five proposed in the revised plan – were replaced by a total of 14 distinct locomotive designs from numerous manufacturers, incorporating many of the diverse (and incompatible) features intended to be tested and evaluated against each other. This limited the theoretical operational benefits and cost savings from the widespread adoption of diesel traction, and many – but not all – of the designs ordered under the accelerated Modernisation Plan were plagued by reliability and service issues, leading to poor availability from the brand new locomotives and leaving some areas of the BR network with a shortage of serviceable traction in the early 1960s. Ironically, in 1967 British Railways drew up a National Traction Plan which rationalised its stock of locomotives and multiple units. Designs that had proved to be the most reliable and operationally efficient were selected for retention and modernisation while the others were designated 'non-standard' and earmarked for quick withdrawal and replacement – a belated implementation of the original pilot scheme which saw many of the locomotives ordered in the late 1950s withdrawn after only a decade in service and in some cases even before the steam locomotives they were intended to supersede.