However, this first little postwar bus family was not destined to live a long life. From spring 1948 to autumn 1950 a total of 649 units left the Sindelfingen plant as complete buses. Including the units supplied to customers as chassis, the production figure for the O 4500 and O 5000 buses was exactly 770 units. Even though their conventional cab-behind-engine design and low-frame construction marked them as members of a species which was gradually nearing extinction, and they would have to leave the field to the forward control vehicles and the self-supporting body design which soon came into fashion, they did have one thing to their credit: making a fresh start, they pointed the way forward in a difficult period and effectively provided urgently needed mobility in their simple, yet elegant way.

In the truck, the engine moves underneath the cab; in the bus, to the rear

As with the trucks of Mercedes-Benz, in the case of the buses it was mainly export customers at first who pressed for forward control variants. From the introduction in summer 1950 of the conventional hooded bus O 6600, derived from the L 6600 truck, it took exactly until spring 1951 to give the O 6600 a little flat-nosed brother. The O 6600 replaced the previous five-ton bus O 5000 in 1950 and had a 145 hp diesel engine from the OM 315 series. This last big cab-behind-engine model from Daimler-Benz was offered for sale until 1955 (from 1954 under the model designation O 304) and attained a production volume of 625 units.

The O 6600 long-nosed bus was launched in the summer of 1950.

The new forward control bus of 1951 was called the O 6600 H. It had a length of eleven meters and an OM 315 engine transversely mounted in its rear end. Further features of this highly up-to-date bus: electrically shifted ZF Media six-speed transmission, bolted-on lightweight steel body, rubber-mounted anti-roll bars. People were surprised.

The O 6600 H was the first ever Mercedes bus to feature a transverse-mounted rear engine.