In February 2015, Serco signed a €200m deal with CAF to purchase 75 coaches of five different types.

[4] These are formed into a total of four 16-coach trains (London Euston to Fort William, Inverness and Aberdeen, London Euston to Edinburgh and Glasgow, plus the two respective return services), plus two coaches for Fort William-Edinburgh-Fort William, with nine coaches as spares, and are hauled by Class 92 locomotives between London and Glasgow/Edinburgh, and Class 73s on unelectrified routes.

[6] Mark 5s commenced operating the London to Edinburgh and Glasgow services in April 2019, with the remainder converted in October 2019.

[7][8] In accordance with the Scottish Government Caledonian Sleeper franchise agreement, Serco's order for purpose-built sleeper rolling stock from CAF originally specified six different types of vehicles to accommodate onboard services and accommodation types.

However, due to safety concerns later arising over aircraft style "pod" seating being incompatible with railway crash worthiness regulations, Serco opted to modify the Mk5 order by requesting that both dedicated and hybrid pod coaches instead be constructed as regular sleeping vehicles.