A step change in GWR open wagon design occurred in 1902 when a fifth plank was added to the previous four-plank open merchandise wagon design. The five-plank became the GWR’s standard wagon design and, essentially, variations on the post-1904 version with a 3ft 3in deep and 8ft body continued to be built well into the 1940s. In many cases the only significant changes were to adopt the latest RCH underframe specifications, a detail invisible to the observer of passing trains.
Initially the diagram O18 wagons were rated at 10 tons this seems to have quickly been increaesd to 12 tons load capacity and like their predecessors used the GWRs then standard 16ft length, 9ft wheelbase steel underframe. The O18 wagons were fitted with GWR self-contained buffers, Dean-Churchward DCIII cross-cornered, spring applied hand brakes and folding sheet support bars to hold tarpaulin above the wagon, allowing water to shed easily and preventing the sheet from sagging and collecting rainwater. In most cases these were removed after the 'common user' wagon pooling system was introduced as this was not a common fitting on wagons from other railway companies.
The main difference was the design of the side door which featured the bottom plank angled outwards at the bottom, unlike the flat doors of preceding diagrams O11 and O15. This was intended to make the bottom plank of the door flat with the wagon floor when opened onto a loading dock and cover the gap left at this joint by a flat door. This made loading and unloading using sack trucks much easier, hence this often being described as 'sack truck' door.
The GWR built 2,850 diagram O18 ‘Open A’ wagons between 1914-1924. As wagons are rarely so well recorded as locomotives it’s not known exactly when the last of these wagons were withdrawn, they slowly disappeared over the years as the cost of repairs exceeded the accountants' allowance, but having robust steel underframes many lasted well into BR days. A batch of O18s was also built for the Rhymney Railway and delivered complete with their own lettering – these were identical, except they were provided without the sheet rail. As British Railways introduced the new standard designs of wagons in the 1950s many older but still serviceable wagons were sold out of service to industry as internal user wagons with small fleets being acquired by the Port of Bristol Authority, Port of London Authority and Manchester Ship Canal. The Port of Bristol finally ceased operating it's own rail system at Avonmouth in the 1970s and many of the surviving wagons were purchased for preservation, resulting in several O18 wagons joining the collections of museum and heritage railways including the Severn Valley Railway and Bristol Harbour Railway.
- GWR No.97199 O18 unfitted 5 plank open wagon
- GWR grey livery with post-1936 lettering
- Disc wheels running in metal bearings
- Supplied with parts for the modeller to attach the optional sheet rail in operational or stowed position
- High level of detail above and below the floor line
- NEM coupler pockets
- 1:76 scale (OO gauge)