The Mercedes-Benz 540 K Streamliner, 1938

Mercedes-Benz 540 K Streamliner (W 29), dimensional drawing. The original drawing is kept in the Mercedes-Benz Classic Archives.

Mercedes-Benz 540 K Streamliner (W 29), vehicle registration document. The original document is kept in the Mercedes-Benz Classic Archives.

Mercedes-Benz 540 K Streamliner (W 29). This photo from 1938 shows the streamlined front section with the broad expanse of its air intake and curved front windscreen. The vehicle was built in 1938 as a one-off model in the special vehicle production unit at the Sindelfingen plant, the objective being to demonstrate the best possible aerodynamic performance. From mid-1938 it was used by the German branch of tyre manufacturer Dunlop in order to test tyres for fast and powerful vehicles.The 1920s and 1930s were characterized, in automotive terms, by the steadily increasing speed of travel. The development of fast roads ways and long-distance routes reflected this change, while the era also saw the advent of the motorway. The automotive industry took advantage of this progress. Not just with more powerful engines and redesigned suspensions: vehicle bodies, for example, grew more sophisticated in design, while streamlined vehicles also emerged.

Against this backdrop, Mercedes-Benz went on to build several vehicles with aerodynamically shaped bodies. The 540 K Streamliner, produced in 1938, marked the culmination in this respect for the time being. The 540 K was Mercedes-Benz’s sporty top model in the 1930s. Customised body shell creations, individually manufactured, had always represented the exclusive norm for Mercedes-Benz, and the “special vehicle production” unit at the Sindelfingen plant made the realisation of such singular ideas possible.

The styling experts at Mercedes-Benz – the term ‘designer’ as we know it today did not yet exist - created a whole series of aerodynamically shaped body shells for the 540 K during 1937 and 1938, all of which reflected the concept of aerodynamic flow to a greater or lesser extent. The Streamliner produced in 1938 was not only a masterpiece of design, but also demonstrated the most thorough application of the knowledge gained in the tests in the wind tunnel.

Achieving even higher cruising speeds than the 140 to 145 km/h usually associated with a 540 K demanded numerous detailed measures. Some of the most important of these involved the car’s aerodynamics: a 540 K in the standard version, with a coupé body, achieved a Cd figure of around 0.57 – too much for higher cruising speeds. For this, a more streamlined body with an considerably improved Cd figure was required. The 540 K Streamliner met the criterion, as wind tunnel measurements undertaken by Mercedes-Benz Classic in May 2014 go to prove: it achieves the exquisite figure of Cd = 0.36. The results are cruising speeds of 165 to 170 km/h and with supercharger a top speed of 185 km/h.

These were the requirements that led to the creation of the body shell of the 540 K Streamliner of 1938. It was systematically designed to meet the aerodynamic specifications: shaped from front to rear to allow the air to flow perfectly over it and to offer as little resistance as possible to the wind. The windscreens are curved to the sides. The roof line is set low, tapering to a point in the middle of the back and merging from there into the horizontal line of the softly curved rear section. The headlamps are fully integrated. At each point where the air flow risks breaking away, the designers have optimised the details, for example by recessing the door handles, omitting the bumpers or reducing the panel gaps. The underbody is completely panelled, so minimising obstructions to the air flow here too.

The requirement to achieve high cruising speeds also dictated an adjustment to the drive axle ratio, which was lengthened from i = 3.08 to i = 2.90. In all other technical details the car matched the standard version of the 540 K.

Just how seriously the builders of the vehicle took their responsibility is demonstrated by the Mercedes star: it does not stand proud, but is painted on – as in the case of the Silver Arrows, the renowned Grand Prix racing cars. Also like these, the streamlined 540 K was given silver paintwork. From today’s perspective it could be seen as something of a historical irony that the classic, vertical Mercedes-Benz pointed radiator grille was nevertheless still to be found below the body shell and remained a decisive factor in the appearance of the front section. Of course practical aspects of thermal management also played a role here, but a styling element that is as characteristic of the brand as the classic Mercedes radiator is subject to special protection - hardly surprising then, that the subject was a talking point at the time right up to Management Board level. This whole process demonstrates the extent to which the automotive industry at the time was changing and how it balanced on the very threshold between the traditional and the modern.

The resulting overall appearance of the 540 K Streamliner was of a powerful sports car, the potential of which to achieve high cruising speeds was immediately clear to the casual observer: doubtless this exceptional one-off vehicle caused a considerable stir when it first appeared.

Much of the praise around this vehicle is also due to Max Sailer. From 1935 on he was a deputy board member of Daimler-Benz and responsible for overall vehicle development for the Mercedes-Benz brand, including for its successful racing and record-breaking vehicles. He was thus very well aware of the significance of aerodynamics in motor vehicle construction and was one of the driving forces behind corresponding projects, also in relation to series-production vehicles.

The extraordinary 540 K was built by the special vehicle production unit in the first half of 1938. In June it was delivered by the Daimler-Benz dealership in Frankfurt am Main to the Deutsche Dunlop Gummi Comp. AG (German Dunlop Rubber Company) in Hanau. The company put this high-performance vehicle to specific use for tyre testing, as the ever-higher speeds at which cars were now travelling demanded new designs and materials for tyres that would enable them to withstand the more powerful forces to which they were exposed. These had then to be subjected to real-life testing, which was all the more necessary for powerful, heavy and fast cars.

And so the 540 K Streamliner really came into its own. Far more so than any other vehicle of that era, its aerodynamically styled body and powerful engine made it eminently capable of rapid supercharged acceleration to speeds as high as 185 km/h on the – in those days still very empty – German autobahns. It smoothly sustains cruising speeds of 165 to 170 km/h over a considerable period. We can only guess at the extreme concentration and tension on the part of the test drivers. Because, at  the speeds at which they were driving, a tyre malfunction was something to be reckoned with at any moment, they were all the more dependent on a reliable and predictable vehicle that would ensure the driver-fitness safety of its occupants over longer periods of driving at the critical limits. The 540 K Streamliner was ideally suited for this task.

Historical dates

According to the commission book Dunlop ordered a 540 K, one of the fastest passenger cars in existence at the time, from the Daimler-Benz dealership in Frankfurt on Main on 23 December 1937. A line drawing, dated 8 February 1938, was produced in the special vehicle production unit headed by Hermann Ahrens. This provided the precise manufacturing specification for a body shell previously tested on the model in the wind tunnel. At around the same time, incidentally, another design with almost identical lines was taking shape on the drawing board, in this case though as a Cabriolet B.

The vehicle ordered by Dunlop appears in the company’s documents dated 10 March 1938 with the comment “Schl. Si.”: Four weeks after the drawing had been made the chassis was trucked from Untertürkheim to the special vehicle production unit at the Sindelfingen plant, where it was fitted with the body that had been assembled there for it. In those days, the final assembly of most Mercedes-Benz passenger cars took place at the Untertürkheim plant, and the body shells were normally transported there from Sindelfingen. In the case of the 540 K it was done the other way round.

Further sources provide the following information: the vehicle registration document was issued by Daimler-Benz on 20 May 1938. Three weeks later, on 14 June 1938, the vehicle was registered in Hanau, where Dunlop was based, and given the registration number IT-146901. Ten days later, on 24 June 1938, an entry appeared in the books of the “Sammelstelle für Nachrichten über Kraftfahrzeuge”, or Central Office of Motor Vehicle Information in Berlin. All this happened even before the streamlined 540 K was handed over to the Daimler-Benz dealership in Frankfurt; and this the commission book records as having taken place on 25 June 1938.

Tyre testing at Dunlop

At Dunlop the vehicle was adopted into the company fleet, where it was looked after by garage foreman Karl Hammes. Hammes was responsible for all test vehicles, managers’ company cars, trucks and even the stables. As soon as the rather involved and time-consuming running-in process required in that era had been completed, Dunlop passed this unusual and elegant vehicle on to fulfil its planned purpose: high-speed tyre testing. Few vehicles can have been better suited to the task. Its streamlined body and powerful engine made it eminently capable of supercharged acceleration to a top speed of around 185 km/h, while its naturally-aspirated engine was then able to sustain cruising speeds of 165 to 170 km/h over long distances.

In a celebratory Dunlop brochure of 1938 we are told: “A particularly tough challenge is set by our tests with a high-speed streamlined supercharged car on the Reichsautobahn, which enable us to study the performance of the tyres at sustained high speeds. Such tests involve a changeover of drivers, driving at speeds of around 170 km per hour. The only stops are for refuelling and for the changeover of drivers, as previously mentioned.”

In order to ensure that the engine could cope with this exceptional sustained load in the upper range, a series of slits were cut in the upper side of the bonnet. These allowed air to flow through the engine compartment and the cooling air then to be discharged, so minimising wind resistance, or drag.

The autobahns, which were new at the time, offered the ideal conditions for testing. The rather special 540 K was often employed on long-distance runs, for example to Berlin or Hamburg and back, sometimes at night, as Gerd Hammes, the son of Dunlop’s garage foreman, remembers. In those days, and with the motorway network far from being complete, this was considered an extraordinary feat of driving. But it was this that made it possible to complete intensive test programmes with high-speed tyres on high-performance vehicles. The most obvious stretch of road to use was the motorway section between Karlsruhe and Göttingen, which had been completed at the beginning of the Second World War. This corresponds to today’s A 5 and A 7 autobahns.

That the car was not spared during its time at Dunlop is shown by traces of wear and tear on those original components that were still available to form part of the rebuilt vehicle some 75 years later - for example at the point where the steering system is mounted onto the chassis.

Following the outbreak of war on 1 September 1939 the non-official use of motor vehicles within the territory of the German Reich was severely restricted. The automotive and accessories industries would feel the impact of this. In order still to be able to drive the 540 K, for example during the ongoing development work, it was converted to run on liquid gas, as an entry in the vehicle documents dated 21 December 1939, authorised by the Director of Police in Hanau, goes to show. A further entry in the registration document – made by the technical inspection authority of district 5 in Frankfurt on 10 April 1940 – provides evidence that the conversion to run on liquid gas increased the unladen weight from 2500 kilograms to 2580 kilograms. The permissible payload was reduced by these additional 80 kilograms to 320 kilograms.

The 540 K survived the period from 1939 to 1945 undamaged. After the end of the war, during which it had been stored in the garages at the Dunlop works, the car was used by a soldier from the US Army, it is thought in the Stuttgart area. It was also he who had it painted to match the army vehicles, as traces of paint found on the original chassis show. A member of staff drew the attention of the manager of the Dunlop branch in Stuttgart, Mr Scheller, to the vehicle’s appearance on the scene. It is presumed that the vehicle was returned to the German Dunlop factory, as it was subsequently deregistered in Hanau on 21 April 1948, as a note in the registration document tells us: “Vehicle recorded as having been taken off the road in accordance with § 3 of the law of 21 November 1947 pertaining to the misuse of motor vehicles.”

The Streamliner would later be returned to the ownership of Daimler-Benz. But quite when and why it is no longer possible to establish. At this point the streamlined body was removed from its chassis, again without anyone today being able to identify or substantiate the reason for this. The note in the vehicle registration document “Chassis/Programme”could possibly be an indication that the plan was to fit a different body to the chassis, due to foreign currency shortages. Conversions of this nature undertaken on other models are well documented. These were fitted with body shells of a more modern design and sold abroad. Not, however, the 540 K Streamliner: the chassis, together with some body components and the rear axle, passed into the inventory of the Museum, where it was furnished in the mid-1950s with a Museum List number (known internally as a “MuLi number”).

The 540 K Streamliner and the “Berlin-Rome” long-distance race

The development of the 540 K Streamliner was begun in 1937 with the intention of building a comfortable, high-performance vehicle that would be able to sustain the high speeds required in the long-distance Berlin–Rome race planned for the late summer of 1938. Over the course of this development work it became clear that it would not be possible to devise solutions to every technical challenge by the due deadline, or certainly not such that would be sufficient to meet the high standards of the Mercedes-Benz engineers. One important aspect, for example, was the durability of the tyres at the speeds to which the team aspired and of which the vehicle was certainly capable.

There were two consequences of this as far as the developers at Mercedes-Benz were concerned: first of all, they decided to use a different variant of the 540 K for the Berlin-Rome long-distance race - one that was already fully developed and tested. The deployment of a short-wheelbase sports roadster, the proposed solution, never came to fruition, however, as the race was cancelled for 1938 and postponed to 1939, then ultimately dropped altogether due to the political situation. Secondly, in mid-1938 they placed the Streamliner at the disposal of the Dunlop tyre works in Hanau, where it was used for high-speed tyre testing – in other words for investigations into precisely those factors which had ultimately led to the decision not to enter the vehicle for the long-distance race.

This 540 K with streamlined body represents a milestone in terms of design and efficiency as well as of handling safety at high speeds. Then, as now, it was impressive for the exceptional professionalism shown by the special vehicle production team at Sindelfingen in the design and detailed implementation of the sheet aluminium body. The meticulously conceived overall concept and altogether perfect execution of this unique vehicle lead us to think that it should not be seen either purely as a competition car or purely as an experimental car. It was surely also built to serve as a prime example of the powerful luxury automobile of the future.