Mercedes-Benz returned to international motorsport in 1955 with enormous resources and the 300 SLR, a sports car derived from the W196 Grand Prix car. The German manufacturer had not entered the World Sportscar Championship in 1954, focused instead on Formula One with Juan Manuel Fangio. In 1955, with Fangio and Stirling Moss under contract, Mercedes approached sports car racing with the same systematic preparation that had made it dominant in F1.
The championship retained the manufacturers-only format. Points on an 8-6-4-3-2-1 scale were awarded to the top six, only each manufacturer's highest-finishing car scored per race, and only the best four results from six rounds counted toward the title.
Seven rounds were originally planned, but two were cancelled. The season opened at the 1000 km Buenos Aires in January and concluded with the Targa Florio in Sicily in October — the latter a new addition to the championship. The 24 Hours of Le Mans and 12 Hours of Sebring, Mille Miglia, and RAC Tourist Trophy formed the European calendar. However, the 1000 km Nürburgring and the Carrera Panamericana were both cancelled as a direct consequence of the Le Mans disaster in June 1955.
The 24 Hours of Le Mans on 11-12 June 1955 became the deadliest accident in motorsport history. On the second hour, Pierre Levegh's Mercedes-Benz 300 SLR was launched into the air in a collision near the pits and broke apart, sending debris into the spectator enclosure. More than 80 spectators were killed. Daimler-Benz withdrew both its remaining cars from the race — which continued to its finish after organising authorities decided stopping it would have caused greater chaos — and subsequently announced the withdrawal of the entire works team from all motorsport at the end of 1955. The immediate cancellation of the Nürburgring and Carrera Panamericana rounds followed.
Mercedes had entered the opening two rounds — Buenos Aires and Sebring — after the Mille Miglia, which fell in May, allowing Ferrari to build a 14-point lead in the early months. At the Mille Miglia, Stirling Moss, aided by journalist Denis Jenkinson navigating with pace notes — then a novel technique — drove to a record-breaking victory in a 300 SLR, covering the open Italian roads at an average speed that remains one of the fastest ever achieved in competitive motorsport. Fangio finished second.
Despite the Le Mans tragedy, Mercedes returned for the RAC Tourist Trophy at Dundrod in Northern Ireland. In a race marred by the deaths of three drivers in separate incidents, Moss and John Fitch led a 1-2-3 Mercedes result, putting the German team back in championship contention. At the final round, the Targa Florio, Moss and Peter Collins won for Mercedes ahead of Fangio, securing enough points to overhaul Ferrari's earlier advantage and take the manufacturers' title.
Mercedes-Benz won the 1955 World Sportscar Championship manufacturers' title, their only season of participation in the championship. Ferrari finished as runner-up. The Mercedes 300 SLR was the dominant car of the season, though its record was complicated by withdrawal at Le Mans and the shadow of the disaster.
The 1955 season transformed international motorsport regulations and safety culture. Le Mans prompted the cancellation of open-road racing events including the Mille Miglia — which continued under political and safety pressure until a fatal accident to the de Portago Ferrari in the 1957 edition finally ended it permanently — and the Carrera Panamericana, which never returned after 1955. Mercedes-Benz's withdrawal from all motorsport at the end of 1955 removed what was arguably the most powerful works team ever assembled from competition, reshaping the entire landscape of both Formula One and sports car racing for the following decade.