The Vlach No.4 was the first successful Czech aircraft, including its Czech engine, a 38 hp Laurin & Klement type L. Beginning in 1908 Metoděj Vlach was employed as the chief mechanic at Laurin & Klement in Mladá Boleslav where his first airplane, an underpowered biplane, was built. His No.4 was already started in 1911 and together with helpers Vítek and Ševit the new monoplane was finished in the summer of 1912 and exhibited at the Mladoboleslavská severočeská výstava (Northern Czech Mlada Boleslav Exposition), there winning the Gold medal.