Class 20
Designed around relatively basic technology, the 73-tonne locomotives produce 1,000 horsepower (750 kW) and can operate at up to 75 mph (121 km/h). Designed to work light mixed freight traffic, they have no train heating facilities. Unusually for British designs, the locomotive had a single cab. This caused serious problems with visibility when travelling nose first, though in these circumstances the driver's view is comparable to that on the steam locomotives that the Class 20s replaced. It was common however to find Class 20s paired together at the nose, with their cabs at opposite ends, ensuring that the driver could quite clearly see the road ahead.
Class 31
Construction of the first locomotive was completed in the final week of September 1957, and the handing-over took place on 31 October. The Class 31 entered service in November 1957, after the launch of the Class 20 locomotive and was one of the Pilot Scheme locomotives ordered by British Railways to replace steam traction. They were originally built with Mirrlees JVS12T 1,250 bhp (930 kW) (D5500–D5519) and 1,365 bhp (1,018 kW) engines and Brush electrical equipment, but the engines were not successful and in 1964 D5677 was fitted with an English Electric 12SVT engine (as used in the Class 37) de-rated to 1,470 bhp (1,100 kW). The trial proved successful, and between 1965 and 1969 the entire class was re-engined. The de-rated engine was used as it was the maximum the electrical system could accept.
Class 37
As part of the large scale dieselisation brought about by the British Rail modernisation plan a need was identified for a number of type 3 locomotives of power output 1,500 hp (1,100 kW) to 1,999 hp (1,491 kW). English Electric had already been successful with orders for type 1 and type 4 diesels, and had produced locomotives of similar power for railways in East Africa. A design based on the exported locomotives was put forward and accepted.The design was for a general purpose locomotive and initially found service in British Rail's Eastern Region. British Railways placed an order for 42 Class 37 locomotives in January 1959. The first was delivered in November 1960; it entered service on 2 December. BR had ordered further Class 37s before last of the original batch had been completed in mid-1962. The final locomotive was delivered to the Western Region on 9 November 1965. English Electric split the construction between Vulcan Foundry at Newton-le-Willows, and Robert Stephenson and Hawthorns of Darlington.
Class 40
A total of 200 were built by English Electric between 1958 and 1962. They were numbered D200-D399. They were for a time the pride of the British Rail early diesel fleet. Despite their initial success, by the time the last examples were entering service they were already being replaced on some top-link duties by more powerful locomotives. As they were slowly relegated from express passenger uses, the type found work on secondary passenger and freight services where they worked for many years. The final locomotives ended regular service in 1985. The Class 40 was powered by English Electric's 16SVT MkII engine developing 2,000 bhp (1,460 kW).
Class 50
The origins of the Class 50 lie in an invitation from the British Transport Commission (BTC) to manufacturers to produce a design for a lightweight Type 4 diesel locomotive with a gross power output of at least 2500 hp. In order to produce a prototype quickly, English Electric based their design on that for their Deltic locomotives which were then in production. Unlike the Deltics, this design was powered by a single engine, the 16CSVT.
Class 55
The British Rail Class 55 built in 1961 and 1962 by English Electric for British Rail. They were designed for the high-speed express passenger services on the East Coast Main Line (ECML) between Edinburgh and London King's Cross. They gained the name "Deltic" from the prototype locomotive, DP1 Deltic . which in turn was named after its Napier Deltic power units.
I have included Class 56s as the engine in these locomotives are derived from the Class 50 engines; When introduced, the Class 56s were arguably the first of the "second generation" of UK diesel locomotives.
The engine is a direct descendant of English Electric CSVT types, its closest relative being the 16CSVT used in the Class 50. Technical advances included significantly uprated turbochargers, gear driven camshafts in place of the timing chain used on Class 50s, and uprated cylinder heads, fuel pumps and injectors. The engine was nominally rated at 3,520 hp (2,620 kW), but was set at 3,250 hp (2,420 kW) for rail use.
