The Mercedes D.III was a German aircraft engine used during World War I. Introduced in 1917, it was a six-cylinder, in-line engine that produced around 160 horsepower. This engine was known for its reliability and performance, making it a popular choice for various fighter aircraft. The Mercedes D.III powered several notable planes, including the Fokker D.VII and the Albatros D.V. Its design featured a water-cooled system, which helped maintain optimal operating temperatures. The engine's efficiency contributed to the success of the aircraft it powered, playing a significant role in the air battles of the war.