GB Railways initially purchased six former Gatwick Express Class 73s. After GBRf won a contract to operate Network Rail infrastructure trains in the south -east, four were overhauled by Fragonset Railways. Subsequently, additional Class 73s were located and purchased, some from preservation, to give a total fleet (at July 2018) of 24 locomotives. Of these, eleven were completely re-engineered in 2014 and 2015, equipped with 1600 hp MTU diesel power units, with five dedicated to Network Rail infrastructure traffic in the south of England, the remaining six being transferred to Scotland for use on the diesel-hauled legs of the Caledonian Sleeper services.