Even in today's age of underwater nuclear power the majority of the world's submarines still use diesel engines as their main source of mechanical power, as they have done since the turn of the century. The diesel-electric submarine propulsion system has changed little in concept since the start of the Great War of 1914-1919. Diesels are used to provide surface propulsion and underwater power is provided from battery driven motors. Diesels are also used to recharge the batteries when the vessel is on the surface or at snort depth. In the 1939-45 War efforts were made by the Germans to perfect the closed or recycled diesel so that the engine could operate underwater independent of a normal air supply. After sporadic revivals of the idea in recent years, the concept has been brought to technical maturity by British and German engineers.However, the history of the submarine diesel engine and its air-dependent versions are nearly as old as the engine itself. The submarine single-power system notion, which came to fruition with the advent of nuclear power, was very popular in the late nineteenth century and the diesel was the-favoured candidate. Research and development in the air-independent diesel began after a few years of the engine's invention and the first patent for such a device was lodged in 1901. However, the development of the air-independent diesel engine system was eventually curtailed because of a fatal accident with a recycled spark ignition engine!In this paper the early years of submarine diesel engine development are chronicled, especially the attemps to produce an air-independent diesel. It is shown that many of the subsequent advances made in diesel engine technology owe their roots to the work of the pre-Great War submarine engine pioneers.