There were two basic types of aircraft engines during the interwar years: the inline water/liquid-cooled type, and the radial air-cooled type. The two types were developed independently and successfully, usually by different companies. This rivalry saw one type or the other in competition for funds and research interest, which tended to retard developmental growth. In addition, two key technologies were crucial to engine development – supercharging and high-octane gasoline – but both of these were developed separately from the engine builders themselves. This resulted in development not being overly responsive to the parent concerns. The position of the commercial aviation industry – which placed emphasis on durability, reliability, and cost effectiveness – was important because its goals were not the same as those of the Air Corps that sought high performance.