The delivery of concrete by ordinary dump trucks from central mixing plants began just prior to World War I. Considerable trial and error experimentation accompanied the development of a suitable truck to meet the needs of the ready mix industry. Stephan Stepanian of Ohio is generally given credit as the first to design a self discharging motorized transit mixer, applying for a patent in 1916. Just when the first concrete truck was placed in operation is difficult to trace. In 1921, a Milwaukee company introduced a truck with an attached mixer that prepared concrete en route to the job sit and discharging its load by gravity. The following year in 1922, transit mixers were reportedly used in street construction work in Missouri. These early transit mixers appear to have been improvisations of concrete mixers to hauling trucks. Following experimentation in the late 1920's, by 1930 several truck manufacturers were offering transit mixers specifically designed as such. Changes in batching equipment and methods at central plants and for transit mixing accompanied the development of truck mixers.