High speed diesel engines are used in most ships.

Marine diesel engines are the main driving force for civilian ships, small and medium-sized ships and conventional submarines (see ship power units). Marine diesel engines can be divided into main engines and auxiliary machines according to their role in the ship. The main engine is used as the propulsion power of the ship, and the auxiliary machine is used to drive the generator, the air compressor or the water pump.

Most ships use supercharged diesel engines (see engine supercharger) and low-power non-supercharged diesel engines are used only on small boats. Most of the low-speed diesel engines are two-stroke machines, the medium-speed diesel engines are mostly four-stroke machines, and the high-speed diesel engines are both. The scavenging form of the marine two-stroke diesel engine has a return scavenging, a port-valve type DC scavenging and an opposed piston type port scavenging. High-powered medium and low-speed diesel engines use heavy oil as fuel, and high-speed diesel engines still use light diesel.