submarine

A submarine is a special kind of boat made to travel underwater for long periods. Unlike ordinary ships, it can dive below the surface and move through the sea while fully submerged. People use submarines for military missions, research, and deep-sea exploration. Early models were small and simple, but modern ones can travel far, stay hidden, and work deep below the waves. The idea also became famous in stories like Jules Verne's Twenty Thousand Leagues Under the Sea.

The word "submarine" literally means "under the sea." It most often refers to a boat built to travel and work underwater. Unlike ordinary surface ships, a submarine is made to dive, stay submerged for long periods, and move safely in deep water. In naval tradition, even very large submarines are often called "boats" rather than "ships."

Historically, submarines have served several purposes. Early models were often built for war. During the American Civil War, the Confederate H.L. Hunley became the first combat submarine to sink an enemy warship. Today, military submarines are highly advanced machines, using sonar, stealth systems, and sometimes nuclear power so they can remain underwater for months.

Submarines are also important for science and exploration. Researchers use them, and related deep-sea craft, to map the seafloor, study volcanic vents, and observe unusual marine life. A famous moment in this kind of exploration came in 1960, when Jacques Piccard and Don Walsh reached the Challenger Deep, the deepest known point in the ocean, in the vessel Trieste.

The word also appears in everyday life through the "submarine sandwich," often shortened to "sub." This is a long sandwich served in a roll and named for its shape, which resembles the long body of the underwater vessel. So the word can point either to a remarkable machine beneath the sea or to a familiar kind of lunch.