when world war i broke out, german military authorities placed orders with rapp motorenwerke. with the influx of capital, the company expanded rapidly and employed 370 workers by 1915. in response to a commission from the german military authorities, karl rapp increased the output of his rapp iii engine from 150 to 175 horsepower. however, the strengthening which this called for made the engine extremely heavy, and the engines developed severe vibrations; so much so, that it achieved no commercial success. even a revised version with four valves per cylinder, the rapp iiia, was unable to rectify this situation: the name rapp had suffered to such an extent that the military departments no longer purchased engines from his company.