The Mercedes-Benz W120 and Mercedes-Benz W121 are technically similar inline-four cylinder sedans made by Daimler-Benz. The W120 was first introduced by Mercedes-Benz in 1953. Powered initially by the company's existing 1.8 liter M136 engine, it was sold as the Mercedes-Benz 180 through 1962. From 1954, Mercedes-Benz also offered the W120 with a diesel engine as the Mercedes-Benz 180 D. The Mercedes-Benz W121 was introduced as the Mercedes-Benz 190 in 1956, powered by a 1.9 liter M121 engine. From 1958, the W121 was also offered with an OM621 engine, sold as the Mercedes-Benz 190 D through 1961. The W120 was nicknamed the Ponton (along with other Mercedes models) after its introduction, because it employed Ponton, or pontoon styling, a prominent styling trend that unified a car's previously articulated hood, body, fenders and running boards into a singular envelope. Together with the longer wheelbase and more luxurious 2.2 liter inline-six cylinder W128 model 220, they constituted 80% of Mercedes-Benz' car production between 1953 and 1959. The W120 was the first predecessor to the medium size Mercedes-Benz E-Class sedan line. History The base 4-cylinder 180 / 190 and the W105 six-cylinder 219 'Ponton' models looked very similar in appearance, from the rear doors forward, to the more luxury W128 and W180 stretched wheelbase six-cylinder 220a and 220 S(E) models. From behind, one could not easily differentiate even the top-of-the-line 220SE (E for 'Einspritzung', or fuel injection) from a base 180 model, but the longer bonnet (and wheelbase), and chrome touches identified it as an upscale, six-cylinder model. The 1951 to 1957 Mercedes-Benz 300 W186 Adenauer company flagship used a much larger frame and body, and was an entirely different car. The 180 and 190 four-cylinders were widely used as German taxis. Only these shorter Pontons featured low-wattage parking clearance lights at front bumper top rear. A simple left-right toggle above and to the left of the driver's knee selected which side would illuminate, so as not to needlessly run down the battery in winter, no small concern when restarting diesels. Heater air intakes were on both sides of the radiator grille only on the W120/W121. The form and body of the car changed little during its production run. However, in 1957, a year after the introduction of the 190 saloon, the 180's M136 engine, which had originally been designed for the Mercedes-Benz 170 Sb, was replaced with a downtuned version of the 190's