The L.N.E.R produced a number of all-steel 21 ton coal hopper designs, starting in 1936 with 2000 wagons being built, though not at the L.N.E.R’s own Carriage and Wagon Works. The engineering workshops that specialised in carriage and wagon construction and
maintenance were principally Cowlairs (formerly of the North British Railway), Shildon, Darlington, Gateshead and York (from the North Eastern Railway), Doncaster (from the Great Northern Railway), Dukinfield and Gorton (Great Central Railway), Hull (Hull & Barnsley Railway) and Stratford and Temple Mills (of the Great Eastern Railway), but for this diagram, loosely being LNER Dia.100, sub-contractors were appointed.
Firms such as Head Wrightson, Hurst Nelson and Metropolitan Cammell submitted their own designs to a basic specification laid down by the L.N.E.R, resulting in no less than 38 variations being identified (source: Model Railway Constructor, Nick Campling, Jim Johnson and Alan Cook). The bulk of the fleet were broadly similar to the illustrated wagon, E270706, the bodywork being riveted, with heavy duty brake gear consisting of four brake shoes per wheel on one side only and long brake levers. Some early vehicles had unusual sole bars lacking a top edge, whilst a proportion of the vehicles had welded bodywork, which became more prevalent during the 1950s as replacement bodies were fitted to existing chassis.
From around 1970, British Rail embarked on a programme of replacing bodies on coal-class wagons and any of the variants could form the donor wagon, leading to the survival of some quite old underframes right into the 1980s. These replacement bodies featured fewer side ribs than the originals, whilst the same time the opportunity was taken to upgrade to roller bearing axleboxes and vacuum fittings, as well as a re-paint into bauxite livery. Overall, 19,200 wagons were built to this general type and all carried British Rail grey livery, with numbers on black patches (featuring the pre-TOPS code of HOP 21) initially.