The D2/12 was mechanically similar to the earlier British Rail Class D2/7 but was of more modern appearance. The engine casing was lower, giving much better all-round visibility.
Ian Allan ABC of British Railways Locomotives, 1966 edition, page 81
Strickland, David C. (1982). Locomotive Directory, every single one there has ever been. Camberley, Surrey: Diesel & Electric Group. p.41. ISBN0-906375-10-X.