Mercedes-Benz MB503 engine
The Mercedes-Benz MB 503 was a German prototype four-stroke V-12 gasoline marine and aircraft engine, designed and concepted before World War II. The MB 503 was based on and derived from the Daimler-Benz DB 603 inverted V-12 aircraft engine. It was a liquid-cooled 12-cylinder inverted V12 enlargement of the DB 601, which was in itself a development of the DB 600. The eventual powerplants chosen to be used in the Panzer VIII Maus super-heavy tank were the MB 509 V-12 gasoline engine, derived from the Daimler-Benz DB 603; and also the MB 517 V-12 diesel engine. See also
 Mercedes-Benz MB507 - Diesel variant based on the Daimler-Benz DB 603. References

Mercedes-Benz engines
Marine engines
Engines by model
Gasoline engines by model
V12 engines