British Railways Mark 1 is the family designation for the first standardised designs of railway carriages built by British Railways (BR) from 1951 until 1974, now used only for charter services on the main lines or on preserved railways. Following nationalisation in 1948, BR had continued to build carriages to the designs of the "Big Four" companies (the Great Western, Southern, London, Midland and Scottish and London and North Eastern railways), and the Mark 1 was intended to be the standard carriage design for use across all lines, incorporating the best features of each of the former companies' designs. It was also designed to be much stronger than previous designs, to provide better protection for passengers in the event of a collision or derailment. The Mark 1 coaches were built in two distinct tranches: the early vehicles (1951–1960) and the 'Commonwealth' stock (named from the type of bogie used) from 1961 onwards. Construction The design was used for hauled passenger stock, multiple unit carriages and non-passenger carrying stock. For passenger stock, construction continued from 1951 to 1963, while multiple units and non-passenger carrying stock continued to be built until 1974. Developed by Derby Carriage & Wagon Works, they were built at Derby, Doncaster, Eastleigh, Swindon, Wolverton and York works. These were constructed in two lengths. Most had underframes long, with bogies at centres; the body was long if the coach was gangwayed, or if non-gangwayed. A smaller number had underframes long, with bogies at centres; the body was long if the carriage was gangwayed, or if non-gangwayed. The shorter vehicles were intended for use where the track curvature was too tight to accommodate the longer vehicles, due to excessive overhang. These lengths allowed for compartments or seating bays wide, plus space for toilets and entrance vestibules; a typical design of Mark 1 vehicle, the TO (Open Third class), had eight seating bays, three entrance vestibules and a pair of toilets at one end. This provided reasonable space. Care was taken to ensure that passengers could enjoy an unobstructed view out of the train from all seats. Seats were aligned to windows and on the long-distance design of Mark 1, the windows had a low sill, just above the floor. An unusual feature of the design was the bodyside tumblehome curvature, of radius and just noticeable; the windows had flat glass and consequently the upper quarter was separate and in a