|Engine:||English Electric 12CSVT diesel
(37/9 fitted with Mirrlees Blackstone MB275Tt or Rushton RK270Tt)
|Power:||1,750 hp (1,305 kW)|
Between 1960 and 1965 309 Class 37s were built by English Electric and proved to be one of the most reliable classes of diesel locomotive built for British Rail . Though with their front end "noses" they were rather dated in appearance when they entered service as other locomotive types had moved to flat fronted designs (indeed they were the last class built for BR with front noses). However the appearance was due to English Electric being reluctant to leave the American styling they had championed since Deltic  and the locomotives reused some tooling and equipment from the earlier Class 40. This reduced the unit price to British Rail which no doubt helped to overcome any doubts over the aesthetics! 
Around 35 are still registered for use on Network Rail and some will remain in service for some time following refurbishments. Many Class 37s have also been preserved.
As can be expected with a large fleet that has remained in service for over 50 years there have been a number of sub-class variants of the Class 37 mostly following a series of refurbishments in the 1980s .
|37/0||Original / unchanged locomotives|
|37/3||Received new bogies|
|37/4||Refurbished and fitted with Electric Train Heating (ETH)|
|37/5||Refurbished but without ETH|
|37/6||Modified to haul heavy freight|
|37/7||Also fitted to haul heavy freight, extra ballast added to aid adhesion|
|37/9||Rebuilt with Mirrlees or Rushton engines for testing for a planned replacement Type 3 locomotive (the Class 38) though this project was later cancelled.|
Four Class 37s have also been rebuilt as 97/3s for a trial project of the European Rail Traffic Management System (ERTMS). They work development trains over the Cambrian line and other Network Rail engineering trains.
|Europhoenix 37 800 at Derby|
|Split headcode front end|
|DRS 37 601 at Crewe|
|Side view of 37 601|
|Colas 37 421 at Derby|
|Network Rail 97 303 at Derby|
 Colin J. Marsden, Traction Recognition (2nd Edition) (Ian Allan, 2008) p. 28
 David Lawrence, British Rail Designed 1948-97 (Ian Allan, 2016) p. 145
 Brian Haresnape, Production Diesel-Electrics Types 1-3 (Ian Allan, 1983) p. 67
 Pip Dunn, British Rail Main Line Locomotives Specification Guide (Crowood Press, 2013) p. 65