The W125 made its first competitive outing in May at the 1937 Tripoli Grand Prix with Mercedes-Benz entering four cars.
German Hermann Lang won his first Grand Prix motor race to give the W125 a victory on its début and provide Mercedes with their first victory over rivals Auto Union since May 1936.
The next race was held at the AVUS motor-racing circuit in Germany, a 12-mile (19 km) long circuit consisting of two long straights of approximately 6 miles (10 km) length joined at either end by a curve.
As such, it was possible for a car to reach its top speed.
Mercedes entered two W125 cars, a streamliner which was modified from the original design to increase its top speed on the straights and a standard car driven by Richard Seaman in case of problems with the streamliner.
The streamliner had a top speed 25 km/h (16 mph) faster than the regular car.
On lap three of the race, the streamliner retired while leading due to a gearbox failure.
Seaman's regular W125 finished in fifth position.

At the Eifelrennen held at the Nürburgring circuit, Mercedes entered five W125's, including one driven by Christian Kautz fitted with the new suction carburettor supercharger system.
Kautz finished in ninth, while teammates Rudolf Caracciola and Manfred von Brauchitsch finished in second and third places.
For the next race, Mercedes split their entries between two races which occurred within a week of another.
Two cars were sent to the USA to compete in the Vanderbilt Cup, one of which was fitted with the suction carburettor supercharger used on Kautz's car, and three cars went to Belgium to compete in the first round of the 1937 European Championship.
Richard Seaman finished second in the Vanderbilt, and third and fourth place were achieved in the Belgian Grand Prix.
Following Seaman's success in the Vanderbilt with the new supercharger system, it was fitted to all of the W125s.

The following two races were also both part of the European Championship.
The next round in Germany saw both Mercedes and rivals Auto Union competing on home soil.
Mercedes triumphed, as Rudolf Caracciola took his first victory of the year and Manfred von Brauchitsch followed him home in second position.
In the next round at Monaco, the positions were reversed as von Brauchitsch won and Caracciola finished in second.
A third Mercedes W125, driven by Christian Kautz, took third place.

The non-championship Coppa Acerbo in Italy was the next event the W125 entered.
During practice Richard Seaman crashed into a house and destroyed his car.
Therefore, only von Brauchitsch and Caracciola started the race.
During the race, Seaman took over from Caracciola and despite an engine fire, he finished the race fifth.
von Brauchitsch fared better finishing in second position.
The Swiss Grand Prix was the penultimate round of the 1937 European Championship.
Like in Monaco, Mercedes W125s finished in the top three places, Caracciola taking the win with Hermann Lang in second and von Brauchitsch third.
The final round of the championship marked a return to Italy, where at the Livorno Circuit, Caracciola held off teammate Lang to win the race by 0.4 seconds and become European Champion.
von Brauchitsch retired from the race and took second place overall in the Championship.
Kautz and Lang took third and fourth places meaning Mercedes drivers occupied the top four positions in the championship table.


The W125 entered into two non-championship events before the end of the season.
The Masaryk Grand Prix in Czechoslovakia gave the W125 its final victory when Caracciola won the race, von Brauchitsch finished second and Seaman came in third.
The race was marred as Hermann Lang had crashed into spectators on lap five, resulting in twelve injuries and two deaths.

 The final competitive race Mercedes entered the W125 into was the 1937 Donington Grand Prix.
Rosemeyer prevailed, von Brauchitsch finished in second place and Caracciola in third while both of the other W125s failed to finish.
The British ERA were outclassed, failing to get classified in their home race.
The W125 made its first competitive outing in May at the 1937 Tripoli Grand Prix with Mercedes-Benz entering four cars. German Hermann Lang won his first Grand Prix motor race to give the W125 a victory on its début and provide Mercedes with their first victory over rivals Auto Union since May 1936. The next race was held at the AVUS motor-racing circuit in Germany, a 12-mile (19 km) long circuit consisting of two long straights of approximately 6 miles (10 km) length joined at either end by a curve. As such, it was possible for a car to reach its top speed. Mercedes entered two W125 cars, a streamliner which was modified from the original design to increase its top speed on the straights and a standard car driven by Richard Seaman in case of problems with the streamliner. The streamliner had a top speed 25 km/h (16 mph) faster than the regular car. On lap three of the race, the streamliner retired while leading due to a gearbox failure. Seaman's regular W125 finished in fifth position.
At the Eifelrennen held at the Nürburgring circuit, Mercedes entered five W125's, including one driven by Christian Kautz fitted with the new suction carburettor supercharger system. Kautz finished in ninth, while teammates Rudolf Caracciola and Manfred von Brauchitsch finished in second and third places. For the next race, Mercedes split their entries between two races which occurred within a week of another. Two cars were sent to the USA to compete in the Vanderbilt Cup, one of which was fitted with the suction carburettor supercharger used on Kautz's car, and three cars went to Belgium to compete in the first round of the 1937 European Championship. Richard Seaman finished second in the Vanderbilt, and third and fourth place were achieved in the Belgian Grand Prix. Following Seaman's success in the Vanderbilt with the new supercharger system, it was fitted to all of the W125s.
The following two races were also both part of the European Championship. The next round in Germany saw both Mercedes and rivals Auto Union competing on home soil. Mercedes triumphed, as Rudolf Caracciola took his first victory of the year and Manfred von Brauchitsch followed him home in second position. In the next round at Monaco, the positions were reversed as von Brauchitsch won and Caracciola finished in second. A third Mercedes W125, driven by Christian Kautz, took third place.
The non-championship Coppa Acerbo in Italy was the next event the W125 entered. During practice Richard Seaman crashed into a house and destroyed his car. Therefore, only von Brauchitsch and Caracciola started the race. During the race, Seaman took over from Caracciola and despite an engine fire, he finished the race fifth. von Brauchitsch fared better finishing in second position. The Swiss Grand Prix was the penultimate round of the 1937 European Championship. Like in Monaco, Mercedes W125s finished in the top three places, Caracciola taking the win with Hermann Lang in second and von Brauchitsch third. The final round of the championship marked a return to Italy, where at the Livorno Circuit, Caracciola held off teammate Lang to win the race by 0.4 seconds and become European Champion. von Brauchitsch retired from the race and took second place overall in the Championship. Kautz and Lang took third and fourth places meaning Mercedes drivers occupied the top four positions in the championship table.

The W125 entered into two non-championship events before the end of the season. The Masaryk Grand Prix in Czechoslovakia gave the W125 its final victory when Caracciola won the race, von Brauchitsch finished second and Seaman came in third. The race was marred as Hermann Lang had crashed into spectators on lap five, resulting in twelve injuries and two deaths.
 The final competitive race Mercedes entered the W125 into was the 1937 Donington Grand Prix. Rosemeyer prevailed, von Brauchitsch finished in second place and Caracciola in third while both of the other W125s failed to finish. The British ERA were outclassed, failing to get classified in their home race.
Mercedes-Benz W125