66721 was delivered in the same shipment as 66718, arriving at Newport Docks aboard MV Jumbo Challenger on 9 April 2006 in First GBRf/Metronet livery.

It was named “Harry Beck” at London Euston on 26 January 2007 by GBRf Managing Director John Smith. Beck created the original diagrammatic Underground map, and the locomotive carried a small engraving of his design on a brass plaque beside the nameplate.

Selected alongside 66718 to receive a special London Transport Museum promotional livery, the locomotive was unveiled on 5 November 2013. The design differed on each side and end: one side depicted Beck’s original 1933 Tube map (with the corresponding No.1 end finished in a more yellow tone), while the opposite side displayed the contemporary 2013 Tube map, with a white No.2 end.

While 66718 was repainted in 2023, 66721 continues to operate in its original vinyl livery, although the Europorte element of the GBRf logo has since been removed. The locomotive has also been fitted with a small Wi-Fi pod above the No.2 cab.