Services (DRS) subsequently bought most of the remaining class 37/4s, for use on nuclear flask traffic. These later found further use in 2018/19 on Cumbrian Coast passenger services and East Anglian passenger services between Norwich and Great Yarmouth/Lowestoft, allowing for multiple units to be cascaded (in the first instance) and covering for accident damaged units (in the second). 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. Class 37/5 This class were updated in similar fashion to the 37/4 subclass, except that they did not receive electric train heating and some were fitted with Sandite ports. Locomotives previously numbered between 37001 and 37119 (those which had split headcode boxes) were given new numbers from 37501 upwards (curtailed at 37521); those previously numbered between 37120 and 37308 were renumbered from 37699 downwards (curtailed at 37667). Nine locomotives from the first batch and three from the second were later modified for use with the aborted Channel Tunnel sleeper Nightstar project, reclassified 37/6 and renumbered 37601–37612 (see below). Class 37/6 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. However, these services were never introduced, and, in 1997, Eurostar sold six of its locomotives to Direct Rail Services (DRS), with a further three sold in 2000. 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. Once Eurostar moved its operations to its new depot at Temple Mills, its Class 37 locomotives became redundant and they too were sold to DRS in 2007. DRS has subsequently sold some of them, Europhoenix being the principal recipient. The Europhoenix 37/6s are used on test trains and have been used to haul EMUs to and from works and to rail-connected scrapyards. Class 37/7 The Class 37/7 sub-class was intended primarily for heavy freight work, with extra ballast and modified gearing. As part of the major refurbishment scheme of the Class 37 locomotives in the 1980s, another freight dedicated fleet of 44 Class 37s was created, the Class 37/7 subclass, which was very similar to the 37/5 subclass except for plating over