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.