A logical design progression from the Class 395 Javelin, the Class 800/801/802 stock have been designed to technical specifications laid down by the Department for Transport, complying with the latest European standards. The main requirements were for the stock to have the flexibility to run on a variety of lines, on gradients up to 1:37, with varying running infrastructure, as well as being adaptable to future transport planning and passenger demands. Running as five car and nine car units, trains can be extended up to a maximum of twelve cars, with a maximum total multiple length of 312 metres, in both bi-mode (dual electric/diesel) and electric forms.