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 of a bodyside window and the addition of a ballast weight to give extra 'pulling power' when hauling heavy freight trains, such as the metals trains in South Wales. Again, like the 37/5s, there were two batches completed; from phase 1 and phase 2 Class 37/0 locos. The batch numbered 37701 upwards (curtailed at 37719) were from phase 1 build locos and have the flush front ends and nose-mounted horns, whilst the batch numbered from 37899 downwards (curtailed at 37 883) were rebuilds from phase 2 locos, having the central headcode box (plated over) and roof-mounted horns. A further batch was created; locos numbered 37796-37803 had a different type of electrical equipment fitted (from Brush), as part of a trial, and differ from the other locos in the subclass internally.