The Napier Deltic engine is an opposed-piston valveless, supercharged uniflow scavenged, two-stroke Diesel engine used in marine (it saw naval service, and is still is use in the Hunt class) and locomotive applications, being used in two types of British rail locomotive classes 55 and 23. The cylinders were divided in three blocks in a triangular arrangement, the blocks forming sides with crankshafts located in each apex of the triangle.