A V18 engine is an eighteen-cylinder piston engine where two banks of nine cylinders are arranged in a V configuration around a common crankshaft. The V18 engine is a rare configuration and is primarily used in large diesel engines running at low operating speeds. These large V18 diesel engines have seen limited use in haul trucks, electricity generation, rail transport, and marine propulsion. There are no known automobiles that have used V18 engines and no engine manufacturer has developed or produced a V18 engine for use in automobiles. While the V18 is a more uncommon engine configuration, there are more common eighteen-cylinder engine configurations such as the W18, which has seen use in both automobiles and aircraft, and the Deltic, an opposed-piston eighteen-cylinder diesel engine created by D. Napier & Son which was used for a variety of applications.