This car was fitted with a DAB V12 engine (82 x 88 mm) of 5,576.75 cc (5.6L, 340.31 CID) with a power of 726 hp (736 PS) at 5,800 rpm.

The weight of this engine caused the car to weigh over the 750 kg maximum limit, so it never appeared in Grand Prix.

Rudolf Uhlenhaut, previously a production car engineer for the company, was selected to lead the design team in late 1936.

[citation needed] When testing the old W25 car, Uhlenhaut remarked that the suspension was too stiff, preventing the wheels from following the road.

[citation needed] The bodywork of the W125 was aluminium, which like its predecessor was left unpainted in its bare silver colour.

[citation needed] The W125 made its first competitive outing in May at the 1937 Tripoli Grand Prix with Mercedes-Benz entering four cars.

[6] 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.

Richard Seaman finished second in the Vanderbilt, and third and fourth place were achieved in the Belgian Grand Prix.

Mercedes triumphed, as Rudolf Caracciola took his first victory of the year and Manfred von Brauchitsch followed him home in second position.

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.

Kautz and Lang took third and fourth places meaning Mercedes drivers occupied the top four positions in the championship table.

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.

[citation needed] The final competitive race Mercedes entered the W125 into was the 1937 Donington Grand Prix.