The start of the war was an arbitrary dividing line for the classification of goods wagons, and did not represent any technological change. This was particularly true for the stake wagons of 1938, which are occasionally referred to as a 'pre-war class' (Vorkriegsbauart) of wagons. For the open wagons, by contrast, not only was a higher maximum load demanded, but also a greater loading volume. As a result, in 1937/38 the Omm wagon was designed from scratch with a maximum load of 24.5 tons and a loading length of 8.72 metres (28.6 ft) (as opposed to 7.72 m or 25.3 ft on Om wagons). Construction began in 1939. Notable external features are the axle base of 6 m (20 ft) and the three-dimensional strut frame that tapers downwards to a point.
