At first, progress was somewhat arduous, but in the 1930s the company’s management took a major step forward by seeking an experienced engineer from a rival firm, whom they found in the figure of Norton’s chief designer, Walter Moore.
Once initial contacts had been made, NSU put forward an irresistible financial offer for the Englishman to join the company based in Neckarsulm. Once established in Germany, Moore played a decisive role in redesigning and improving the quality of the range, while simultaneously bringing it closer to the typical standard of British motorcycles, then considered the finest in the world. With a renewed line-up of elegant, high-quality machines, NSU’s sales surged and the success would endure for many years, to the point that in the 1950s the marque became the world’s largest motorcycle manufacturer.
It was therefore only natural that, throughout the 1930s, the German Army studied the range and commissioned militarised versions of two of NSU’s touring models, namely the 601 OSL and the 251 OSL presented here. This was a 242cc motorcycle built in large numbers, with a single cylinder and very low fuel consumption. The intention was to deploy the 251 OSL as a liaison vehicle or for military dispatch riders. The letters OSL stood respectively for: O, overhead valve; S, sport; and L, the luxury version with various extras such as an electric horn, speedometer, or even chromed elements, which were rarely used on military models.
The NSU 251 OSL was produced between 1936 and 1942, with the militarised version appearing in 1938. Owing to shortages of raw materials, the 1942 models replaced the aluminium engine block with a cast-iron version, naturally heavier, and this served in both variants until the end of the conflict.