The Napier Deltic is an unusual type of diesel engine. It was used in boats and railway locomotives.[1] The cylinders are arranged in a triangular form with two pistons in each cylinder. There are three crankshafts which are geared together at one end of the engine. These engines usually had nine cylinders (three banks of three) or eighteen cylinders (six banks of three). These engines were built by D. Napier & Son.