with his fellow driver Louis Chiron, but a crash in practice for the Monaco Grand Prix left him with multiple fractures of his right thigh, which ruled him out of racing for more than a year.

After he retired, Caracciola worked as a Mercedes-Benz salesman targeting North Atlantic Treaty Organization (NATO) troops stationed in Europe.

Rosenberger lost control at the North Curve on the eighth lap when trying to pass a slower car, and crashed into the timekeepers' box, killing all three occupants; Caracciola kept driving.

Caracciola, driving a 7.1-litre Mercedes-Benz SSK, started from the back row of the grid (which was allocated randomly), and battled Bugatti driver William Grover-Williams for the lead early on.

[27] Mercedes-Benz officially withdrew from motor racing in 1931—citing the global economic downturn as a reason for their decision—although they continued to support Caracciola and a few other drivers covertly, retaining manager Alfred Neubauer to run the 'independent' operation.

[28] In part because of the financial situation, Caracciola was the only Mercedes driver to appear at the 1931 Monaco Grand Prix, driving an SSKL (a lighter version of the SSK).

The local fleet of Alfa Romeos battled for the lead early in the race, but when they fell back Caracciola in his SSKL was able to take control.

He ran fourth early in the race, but moved to second as Alfa Romeo driver Baconin Borzacchini pitted for a wheel change and the axle on Achille Varzi's Bugatti broke.

[40] Caracciola performed strongly in other races; he won the Polish and Monza Grands Prix and the Eifelrennen at the Nürburgring, and took five more hill climbs to win that Championship for the third and final time.

Von Brauchitsch drove a privately entered SSK with streamlined bodywork and beat Caracciola's Alfa Romeo, which finished in second place.

Caracciola was seen by the German crowd as having defected to the Italian team and was booed, while von Brauchitsch's all-German victory drew mass support.

He was close friends with the French-Monegasque driver Louis Chiron, who had been fired from Bugatti, and while on vacation in Arosa in Switzerland the two decided to form their own team, Scuderia C.C.

[48][49] Caracciola defied the predictions of his doctors and healed faster than expected, and in the winter Charlotte took her husband back to Arosa, where the altitude and fresh air would aid his recovery.

[50] Alfred Neubauer, the Mercedes racing manager, travelled to the Caracciolas' chalet in Lugano in November with a plan to sign him for the 1934 Grand Prix season if he was fit.

[53] Caracciola tested the new Mercedes-Benz W25 at the AVUS track in April, and despite his injuries—his right leg had healed five 5 centimetres (2.0 in) shorter than his left, leaving him with a noticeable limp—he was cleared to race.

[58] His best results in the rest of the season were a second place in the Spanish Grand Prix—he led before Fagioli passed him, much to the anger of Neubauer, who had ordered the Italian to hold position—and first at the Klausenpass hillclimb.

[60] He opened the Championship season with a pole in Monaco but he retired just after the half of the race, then he won in France and took the lead of the standings with another win in Belgium, ahead of Fagioli and von Brauchitsch, who shared the other Mercedes-Benz W25.

The Swiss Grand Prix was held at the Bremgarten Circuit in Bern, and Caracciola won from Fagioli and the new Auto Union star Bernd Rosemeyer.

[69] Mercedes were so uncompetitive in 1936—Caracciola won only twice, in Monaco and Tunis—that Neubauer withdrew the team mid-season, leaving Rosemeyer to take the Championship for Auto Union.

[73] Driving a streamlined Mercedes-Benz, Caracciola won his heat against Rosemeyer, averaging around 250 kilometres per hour (160 mph), although a transmission failure forced him to retire in the final.

[79] The Mercedes-Benz drivers took the lead from each other several times, but von Brauchitsch won after a screw fell into Caracciola's induction system during a pit stop, costing him three and a half minutes.

Despite heavy rain which made the Bremgarten Circuit slippery and hazardous, Caracciola set a new lap record, at an average speed of 169 kilometres per hour (105 mph), and cemented his reputation as the Regenmeister.

[81] Caracciola took pole position, and despite two false starts caused by spectators pouring onto the track, held his lead for the majority of the race and won from his teammate Lang by just 0.4 seconds.

[93] Mercedes-Benz' new car, the W154, proved its abilities at the French Grand Prix, where von Brauchitsch won ahead of Caracciola and Lang to make it a Mercedes 1–2–3.

The change was, however, leaked to Mercedes-Benz well in advance, and in just eight months the firm developed and built two W165s under the new restrictions; both of them beat the combined might of 28 Italian cars, much to the disappointment of the organisers.

[101] Caracciola believed that the Mercedes-Benz team were favouring Lang during the 1939 season; in a letter sent to Mercedes' brand owner Daimler-Benz CEO Dr. Wilhelm Kissel, he wrote: I see little chance of the situation changing at all.

Yet this will be hardly possible in the future, as almost all the mechanics and engine specialists in the racing division are on Lang's side ...[102]Despite Caracciola's protests, Lang was declared the 1939 European Champion by the NSKK (Nationalsozialistisches Kraftfahrkorps, or National Socialist Motor Corps)—although this was never ratified by the AIACR, and Auto Union driver Hermann Paul Müller may have a valid claim to the title under the official scoring system—and motor racing was put on hold upon the outbreak of war.

[107][110] Tony Hulman, owner of the Indianapolis Motor Speedway, invited Caracciola and his wife to stay at his lodge near Terre Haute to let him fully recover.

[113] Caracciola's career ended with his third major crash; during a support race for the 1952 Swiss Grand Prix, the brakes on his 300SL locked and he skidded into a tree at the fast, tree-lined Bremgarten circuit, fracturing his left leg.

After races in Germany the drivers took part in presentations to the crowd coordinated by NSKK leader Adolf Hühnlein and attended by senior Nazis.