The Class 66 is a Co-Co diesel-electric  freight locomotive introduced to Britain in June 1998. Over 500  locomotives were built, the final one being delivered to GB Railfreight  in the spring of 2016.

Delivered into Newport Docks on board the  MV Jumbo Challenger in April 2006, 66721 first went into service with  Metronet/First GBRf, carrying the Metronet livery of blue bodysides and  roof, with orange cab sides, cantrail and solebar stripes, until the  beginning of November 2013.

On 26 January 2007, 66721 was named  'Harry Beck', by John Smith, MD of GB Railfreight, in honour of the  graphic designer who created the London Underground Tube map in 1933  using a design grid based on an electrical schematic.