their first submarine by an Irish man named John Holland. From 1945 to 1955, tremendous changes were made for a great time when the first submarine was sent out to sail for the first time. The United States heavily depended on the submarines as a weapon of war when they were going to war with the Japanese. Age of Steam Steam was first applied to boats in the 1770s. With the advent of economical steam engines, efficient external combustion heat engines that makes use of the heat energy that exists in steam and converting it to mechanical work, the prime mover was steam for ships. The technology only became relevant to sea travel after 1815, the year Pierre Andriel crossed the English Channel aboard the steamship Élise. Rise of steam vessels Steamships gradually replaced sailing ships for commercial shipping in the 19th century – mostly through the latter part of the century. Paradoxically, steam supported sail, by providing tugs that could speed the arrival of ships that could often be windbound in anchorages close to their point of departure or destination. Larger sailing vessels could be built for bulk cargoes, as the availability of tugs meant that they could be docked efficiently. Steam "donkey engines" enabled these larger ships to work with smaller crews, being used for hoisting large sails and generally doing the heavy work on the ship. Steam technology required a number of developmental steps to be able to compete with sail propulsion. Better materials and designs were needed for the boilers that ran at the higher pressures that allowed the increases in fuel efficiency from, first, compound engines (successfully used in SS Agamemnon (1865)) and then the triple expansion engine (starting with SS Aberdeen (1881)). The practice of using sea water in boilers caused build up of salt in the boilers, so requiring regular cleaning on route. An interim solution was to regularly replace the water, to keep the salt content low – needing development of heat exchangers to recover the heat from old water. Ultimately condensers were designed to recover the fresh water used in later boilers. The inherent problems of paddlewheel propulsion were solved by the screw propeller, but that needed a functional stern gland and thrust bearing. Iron hulls overcame the structural issues of wooden-hulled steamers, but needed anti-fouling materials, or, failing that, dry docks in which hulls could be regularly cleaned. For steamships