Mercedes-Benz W 125 record car, 1937

The record runs of the two rivals Daimler-Benz and Auto Union, which had been highly successful in terms of propaganda at both the national and international level since 1934, culminated in 1937 in a central event organised by the Supreme National Sports Commission for Automobile Sport in Germany (ONS) and the National Socialist Motor Vehicle Corps (NSKK), which, as a sub-organisation of the NSDAP, had in the meantime effectively appropriated the sovereign rights of the ONS. From now on, the "record week" was to bundle the increasingly intense competition between the two players from Untertürkheim and Zwickau in institutionalised form - and thus optimally suitable for the political goals of the ruling powers at the time. Every year in autumn, the two main protagonists were to spur each other on to ever new best performances during "record week".

For this occasion, a completely newly developed record-breaking car was built at Daimler-Benz. The chassis was taken from the new W 125 Grand Prix racing car, and the streamlined bodywork was also completely redesigned. The development goal had been to reduce the frontal area and the Cd value compared to the previous year's model.

Significant progress had been made with the power unit. Designed from 1935 onwards by engineer Albert Heess, the nearly 5.6-litre V12 engine, designated MD 25 DAB, was quite heavy due to the adherence to the traditional design of Mercedes-Benz racing engines with steel cylinders and welded-on sheet steel cooling jackets, but a lack of power was not its problem.

In the year before it had already reached a power level of 616 hp/453 kW at 5800 rpm. With the transition from the hermetically sealed pressure carburettors to two float carburettors positioned between the blower and the air intake, this value was once again significantly increased. Thus, in the run-up to the record attempt, the high-revving, only slightly long-stroke V12 provided a maximum output of 736 hp/541 kW at 5800 rpm on the engine test bench.

The powerful V12 engine was not to become the limiting factor during the record week in 1937 - rather, the visually harmonious, fully streamlined body of the new W 125 record-breaking car lacked aerodynamic efficiency. This was directly reflected in the results of the record-setting attempts. On its first run on 25 October 1937, the car reached 366 km/h for the flying kilometre and 358 km/h for the flying mile. On the second run on the same day, it was not possible to drive at full throttle because the car lifted off at the front. Since the engine was also weak, apparently as a result of a defective piston, the Daimler-Benz racing team abandoned the attempts. Bernd Rosemeyer in the Auto Union was much luckier: he drove the flying kilometre at 406.3 km/h and the flying mile at 406.2 km/h.

Three days later, the Untertürkheim team was back. The modified car, loaded with a 46 kg lead weight on the front axle, eventually reached speeds of 398.89 km/h for the flying kilometre and 397.08 km/h for the flying mile. After the engine ran poorly again on the third run of the day and the driving stability also left much to be desired, Daimler-Benz withdrew from the 1937 record week and left the field to the competition from Zwickau.

For the next attempt, during the 1938 record week, the body had to be fundamentally reworked.