Propulsion is the system which creates the lift of a ship. Technological advancement has introduced new propulsion mechanisms, influencing and shaping our society as we know it today.Oars and sails were the first tools used for propulsion. The marine steam engine made its appearance at the start of the 19th century. During the 20th century, it was replaced by steam-turbines which gave their place to two and four-stroke engines. Naval nuclear reactors made their appearance during the 1950s. The generated steam is used to produce power for the propulsion of warships and icebreakers. Lately, more and more ships are built with electrical propulsion. Generators, powered by internal combustion engines, produce electrical power used for propulsion and other general uses.Lastly, because of the increasing environmental requirements, there exists new applications where electrical power is generated from liquefied natural gas (LNG) or hydrogen fuel cells, or a combination of other methods. Experimental technologies that try to help reduce the energy footprint, produce power with solar panels. The advancements of hybrid ships gains ground, having the advantages of low emission.