[3] The Class 37 became a familiar sight on many parts of the British Rail network, in particular forming the main motive power for InterCity services in East Anglia and within Scotland.

Vehicles from D6819 onwards were built without nose-end doors and the headcode display was changed from a split pair of boxes to a panel on the centre of the nose.

[9] Seven orders were placed with English Electric, as follows:[10] The class was designed for freight work and to haul passenger trains on secondary routes and as such the gearing was kept low.

On delivery, the Class 37s were painted in plain green with a grey roof, the 'late' (post-1956) British Railways crest and a D prefix to their running number.

This entailed the yellow nose continuing round to behind the driver's door and up to the top of the windscreen and a full height 'double arrow' logo.

The first was a group of 12 Motherwell allocated locos that were fitted with strengthened couplings and modified brake blocks for working the heavy trains to Ravenscraig.

[citation needed] Starting in 1979 triple-heading on iron ore hoppers between Port Talbot and Llanwern in South Wales commenced, typically using locomotives in the range 37 299-37 308.

Between 2019 and early 2020 Colas Rail hired three Class 37s, including 37418 and 37421, to Transport for Wales for use (once again) on peak hour commuter services on the Rhymney line.

Eurostar (at the time European Passenger Services) had 12 locomotives modified (all ex-37/5) as Class 37/6, with the intention that they would haul overnight international trains ("Nightstar") over the non-electrified sections of their routes in Britain.

The remaining three locomotives were retained by Eurostar for a variety of tasks, including driver training, route learning, and for rescuing failed Class 373 units.

[citation needed] The Class 37/7 sub-class was intended primarily for heavy freight work, with extra ballast and modified gearing.

They operated merry-go-round trains of 32-ton HAA air-braked hoppers, usually numbering 32 wagons, between collieries, washeries, open cast mines and disposal points to power stations such as Aberthaw and occasionally further afield.

Cardiff had a large allocation of 37/7s, some waiting on standby, ready for a call from the mills requiring more wagons to handle any extra traffic.

They all had modifications similar to that of Class 37/7, including new nose grilles, removal of the central bodyside windows and 4 fire extinguisher ports.

All six Class 37/9s were delivered in Railfreight Grey livery, later receiving 3TG metals sub sector livery, and operated as part of the British Rail Heavy Metals sector, being based in South Wales and hauling trains normally rostered for the much more powerful Class 56 such as the Port Talbot Steelworks–Llanwern Iron Ore tipplers.

[12] By the late 1970s Class 37s were handling the loco-hauled services west of Swansea to Fishguard Harbour, Milford Haven and Carmarthen although operations to Pembroke Dock remained the exclusive preserve of DMUs.

[28][30] and also on the Western Region, in early 1978 Plymouth Laira received 37 142 from Landore and 37 267 from Stratford to be used on China Clay traffic in place of double-headed Class 25s.

[31] Also around this time and on the other side of the country Class 37 locomotives having the later design of nose with the central headcode box were banned from operating into Liverpool Street over concerns about the clearance between the overhead catenary and the roof-mounted horns.

One short-lived experiment involved 37175 receiving CP5 'self-steering bogies' designed to reduce excess wear and noise on the tightly curved West Highland line to Fort William and Mallaig.

Some Inverness allocated Class 37s received 'car lights'; these were essentially spotlights that made them more visible on the sharply curved Scottish branches, especially to users of level crossings.

However, second-hand Class 37s have also proved popular in the export market, with some examples operating in Spain and France, serving the construction of those countries' high-speed railway networks.

Additionally, Colas purchased 37146, 37188 and 37207 with the intention of returning them to main line duty but, as of March 2020, 37146 is unlikely to receive its intended overhaul and is expected to be sold or used as a parts donor.

Most of the DRS 37s were used on nuclear flask services coming from a host of places including Hunterston, Torness, Heysham, Hartlepool, Sizewell, Bridgwater, Valley and Dungeness, but are now being replaced by Class 68s.

[42] DRS Class 37s were hired to power passenger services on the Wherry lines (Norwich to Great Yarmouth/Lowestoft) for Greater Anglia between June 2015 and September 2019, due to a shortage of diesel multiple units, as a result of two serious accidents.

On 16 December, 37 417 suffered serious engine failure and was sent to Eastleigh for storage, resulting in 37401 becoming the only Class 37 to remain in traffic into the new DB Schenker era.

37401, DB Schenker's sole operational English Electric Type 3 at the time, was reported sounding rough and was later stored, although this did not last long, as it was soon sent to Toton TMD for repairs along with 37406 The Saltire Society.

37419 was prepared for a return to traffic and repainted into DB Schenker livery, however its long time in store did not help its power unit and it failed with a serious engine fault on its trial run.

37800 and 37884 were bought by Europhoenix and once restored to working order, went on long term hire to Rail Operations Group in a dual Europhoenix/ROG livery.

These locos were effectively refurbished, having been completely stripped down to bare steel, with reconditioned engines, somewhat updated cabs, all new signalling systems installed (ERTMS in this instance) and extensive re-wiring.

[84] In 2008, Bachmann introduced a couple of versions of the locomotive in OO gauge, which included DCC sound: 37057 with the unofficial name of Viking, and 37698 Coedbach in two-tone grey Railfreight Coal livery.