Their use on Metals Sector trains, usually from Llanwern, Port Talbot or English metal works such as Scunthorpe, saw them hauling very heavy trains between docks, works and purchasers in Britain. Indeed, the use of three Class 37/0 locomotives on Llanwern-Port Talbot Docks steel trains (the heaviest on the British rail network at was soon abandoned when Class 56s became available, requiring only two locomotives. 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. Eventually this work was taken over by Class 56s and Class 60s. This Metals traffic would also become the domain of the sub-class 37/9, which to all intents and purposes was a 37/7 but with a different prime mover.