374-738B BR Mk2F TSO Tourist Second Open BR InterCity (Swallow) No. 5951British Rails second generation of standard coach was designated the Mk2, following on from the highly successful Mk1 series. Unlike the Mk1s however, the Mk2s evolved through different build batches, and such were the changes that a letter suffix was attributed to identify each of the different variants. Fewer coach types were built, with construction concentrating on vehicles offering standard accommodation of both first and second class, plus