This class were updated in similar fashion to the 37/4 subclass, except 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; those previously numbered between 37120 and 37308 were renumbered from 37699 downwards (locomotives 37601-37613 were Class 37/6, not Class 37/5).