British Rail Mark 1

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British Rail Mark 1
Mark 1 Open First on Commonwealth bogies at Tyne Yard in March 2009
Interior of a Mark 1 SO (Second Open) Colne Valley Railway
In service	1951–present
Manufacturer	British Railways Cravens Gloucester Railway Carriage & Wagon Company
Built at	Derby Doncaster Eastleigh Swindon Wolverton York
Constructed	1951–1963
Operators	British Railways
Specifications
Car body construction	Steel Body-on-frame, non-integral
Car length	57 ft 0 in (17.37 m) or 63 ft 6 in (19.35 m)
Doors	Slam
Maximum speed	90 or 100 mph 140 or 160 km/h
HVAC	Steam or electric or both
Bogies	BR1, BR2, Commonwealth or B4
Braking system(s)	automatic vacuum, air, or dual
Coupling system	Drawhook or retractable knuckle coupler resting on drawhook
Track gauge	4 ft 8+1⁄2 in (1,435 mm) standard gauge

British Rail 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, from 1961 onwards, the "Commonwealth" stock – so named on account of their bogies, which were a variant of the bogie designed by the General Steel Castings Corporation (formerly named the Commonwealth Steel Company) of Granite City, United States of America.