The British Railways Mk1 was the designation given to BR's first standard design of main line coaching stock, and one of its most successful. Built from 1951 until the early 1960s to augment and replace the array of 'Big Four' and earlier 'pre-grouping' designs inherited from the LMS, LNER, GWR and SR, BR took the best features from several of these types to produce the new steel-bodied design. As a result, the Mk1 was stronger and safer than any of the inherited types that came before it.