The Opel 4/12 PS, manufactured by Opel in Ruesselsheim from 1924 to 1931, was the first German car produced on assembly lines.
The popular 2-seater was known as the “Laubfrosch” (German for tree frog) because it was available in green only, to keep the costs low.
The small car with a kerb weight of 570 kg and a straight-4 engine had a top speed of 60 km/h. The Opel 4/12 PS resembled the Citroën 5 CV that was mainly painted in yellow.
The only differences were that the Opel’s wheelbase was longer by 5 mm, the radiator looked different, the water cooled 4-cylinder engine was bigger, and a 12-volt electrical system was used instead of the commonly used 6-volt system. It never was clear whether in Ruesselsheim the Citroën was produced under license or the design was simply copied by Opel. About 120,000 units were produced before the successor the Opel 1.2 Liter was introduced in 1931.

