Submarines The first military submarines could only travel for short distances while underwater During World War I 1914 1918 submarines were made with sturdy double hulls an outer hull and an inner hull called a pressure hull The pressure hull had ballast tanks that could be filled with air or water to make them rise or sink To steer while diving underwater the subs used movable short wings at the stern or back called hydroplanes A conning tower also called a fin or sail helped to keep the submarine stable It housed sensors as well as periscopes for looking around and above objects Batteries powered the sub’s electric 4
motors while submerged By the end of World War II 1939 1945 submarines spent most of their time at the surface In the 1950s nuclear power allowed subs to stay underwater longer Modern submarines SSBNs have become large platforms for nuclear ballistic missiles Others called hunter-killers SSNs are designed to destroy SSBNs This Japanese Sōryū-class diesel-electric fast attack submarine uses Stirling engines These engines do not need air for pressure to help the sub remain submerged for long periods of time 5
