In 1949, an assembly cooperation agreement was signed with Fiat in Turin. In 1943, an underground factory for the Steyr-Daimler-Puch company was built in Gusen. Some parts of the quarries were converted into a Mauser machine pistol assembly plant. The list of companies using slave labour from the Mauthausen-Gusen camp system was long, and included both national corporations and small, local firms and communities. Puch is on Wikipedia's list of companies using slave labour from the Mauthausen-Gusen concentration camp system. In the three original assembly halls, luxury vehicles for the American market were produced. The existing capacity was insufficient, therefore a second plant was constructed and opened in 1941 in Thondorf, Graz. Like all enterprises of its kind, the Puch production plants had to change to arms production during World War II. This company in its turn merged in 1934 with Steyr AG to form Steyr-Daimler-Puch. In 1928 the company merged with Austro-Daimler and became a part of the new Austro-Daimler-Puchwerke. In 1923 the double-piston motor was patented. However with the collapse of the empire following the War, the market for automobiles shrank and production was discontinued. During World War I, Puch became an important vehicle supplier to the Austro-Hungarian Army. In that year the company employed about 1,100 workers and produced 16,000 bicycles and over 300 motorcycles and cars annually.
In 1912 Johann Puch went into retirement and became the company's honorary president. In 1912, the 38 PS (horsepower) Type VIII " Alpenwagen" was developed. In 1910, Puch even produced sedans for members of the imperial family.
In 1906 the production of the two-cylinder Puch Voiturette began and in 1909 a Puch car broke the world high-speed record with 130,4 km/h. Production of engines was started in 1901 and cars followed in 1904. The main production plant, later called " Einser-Werk", was constructed in the south of Graz, in the district of Puntigam. It soon began producing motorcycles and mopeds. Puch's company became successful through innovation and quality handicraft, rapidly expanding over time. Ten years later he founded his company, "Erste Steiermärkische Fahrradfabrik AG" (English: "First Styrian Bicycle AG"). Johann Puch first produced bicycles in 1889 in a small workshop called " Fahrradfabrikation Strauchergasse 18 a" in Graz.