Its distinctive humming exhaust note led to it being nicknamed "Humlebien" ("Bumblebee"). The first customer received his Type C in the summer of 1934 and thanks to an efficient dealer network, the Bumblebee soon became the best-selling motorcycle in Denmark. The Danish Post Office, Army and Police purchased substantial numbers of this model and in 1939 as war loomed, the Danish government spent DKK 50 million on motorising the army and many Type Cs were included in this expenditure. During the occupation by German forces from 1940 to 1945, it was difficult for Fisker & Nielsen to obtain the materials needed for motorcycle production and only about 600 machines were made during the period. Shortly after World War II, a much improved ohv engine was built and tested. Seeing, however, that the factory had no trouble selling every motorcycle built, it was decided not to make any major investments in new tooling. Instead more minor improvements were made to the existing models, usually making it possible to upgrade older models. The Danish Army bought around 20% of Fisker & Nielsen's total production, which no doubt influenced the decision not to introduce a new model; the military would be unlikely to want an enlarged spares inventory to support an additional model. The Postal Service bought many Type C models, using them as late as 1972. The Danish police force was also a large customer but phased out their Nimbuses much earlier in the late 1950s and early 1960s when they became too slow to keep up with modern cars and motorcycles; the top speed of a stock solo bike was only , and that for brief bursts only. Very few were exported. In the 1950s some further prototypes were built, like a four-cylinder with a rotary valve and carbon seals as well as a two-cylinder model with sprung rear suspension, neither of which reached production. Several prototypes with sprung rear suspension and an Earles front fork also were built. Many details of the "″Bumblebee" were changed during its lifespan, major ones being a switch from hand to foot gear change, larger brakes (150mm to 180mm) and an improved front fork (the "High" fork). Still, the basic design was never updated and as interest in motorcycles declined in the late 1950s as a consequence of the availability of cheap cars such as the Volkswagen Beetle, production ceased in 1959, when the last contract from the army was delivered. The Nimbus now has attained almost iconic status, not only in Denmark but also abroad where its very individual character makes it a machine of unusual technical interest.