Sliding-wall wagons German wagon classes: K…g… UIC classification: H…i… The present-day standard wagon for moisture-susceptible palletised goods has sliding sides rather than fixed side walls, which enables access to the entire loading area for loading and unloading. These wagons with sliding walls or sides did not evolve from the original covered wagon, but were derived in the 1950s from wagons with sliding roofs and sides, which is why they used to be grouped in Class K. The DB has over 15,000 sliding-roof wagons. Wagons built up to the early 1980s have a loading area of without partitions and can take a maximum of 30 Europool pallets (code letter b). On the more recent types were the dimensions were optimised: on of loading area (without partitions) up to 40 Europool pallets can be carried (Code letter bb). In addition to making best use of the loading area there has been a trend towards large-volume wagons, which make maximum use of the available loading gauge. However they need to take account of the fact that in many countries the permitted loading gauge varies and this reduces the interoperability of this vehicle. The wagons cleared for use in Great Britain have a very small loading gauge and are distinguished by the code letters f, ff or fff. Other countries with small loading gauges include Switzerland, something which needs to be borne in mind for trains transiting the country e.g. between Germany and Italy. Sliding-wall wagons are often fitted with partitions that prevent the goods sliding back and forth in the wagon (code letter l) and some are lockable (code letter ll). This is particularly useful if the wagon is not fully laden. However the use of partitions reduces the available loading area. Historical development Germany To begin with, the largely privately owned railway companies within the German Empire in the 19th century procured wagons to their own requirements. However, after the nationalisation of the majority of private railways into the state railway (the Länderbahnen) designs were standardised and the Länderbahn classes emerged. The growth in trade between the various German-speaking states led to attempts to standardise their vehicle fleets. Initially wagons were produced to the same dimensions and, in 1910, the German State Railway Wagon Association (Deutsche Staatsbahnwagenverband) was formed. They developed standard goods wagon designs, the so-called Verbandsbauart wagons, that were procured in large numbers by the German state railways and other