A ship is a vessel for conveying passengers and freight by water. Modern ocean-going ships developed from early sailing ships, such as the carracks (Mediterranean merchant ships) of the thirteenth century and larger early ships called galleons. Fighting ships of the seventeenth and eighteenth centuries included frigates of various designs; later models had several rows of guns. Sailing freighters led to the development of the great clippers of the late nineteenth century, some of which had iron hulls. A century or so earlier, the first steamships had been built. They were powered by wood- or coal-burning steam engines that drove large paddle wheels, hence the term paddlesteamer.
In 1819 the first Atlantic crossing was made by "steam-assisted sail" and this crossing soon became a regular service. By the mid-nineteenth century steamships driven by propellers or screws, were in general service and were voyaging on trade missions in all oceans. Marine steam turbines were developed at the turn of the nineteenth century and gradually replaced reciprocating (back-and-forth cranking) steam engines for large vessels, examples being ocean liners of the early 1900s with displacements (weight of water that a ship displaces when fully laden) up to 10,000 metric tons. Oil, rather than coal, was now the favorite fuel for large marine engines.
Some of the newest military ships and icebreakers are fitted with nuclear engines in which heat from a nuclear reactor raises steam in boilers to drive steam turbines. The larger modern ships are classified as warships, passenger vessels, bulk dry cargo ships, tankers for bulk liquids, freighters for mixed cargo, and container ships. The largest of these are the supertankers carrying oil, with displacements of about half a million metric tons and lengths of several meters.