Explained: How does a Submarine work?

A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. It is also sometimes used historically or colloquially to refer to remotely operated vehicles and robots, as well as medium-sized or smaller vessels, such as the midget submarine and the wet sub. Submarines are referred to as "boats" rather than "ships" irrespective of their 

What is a submarine?

Oceans are most turbulent where wind meets water: on their surface. The waves that race across the sea are a sign of energy, originally transmitted by the Sun and whipped up into winds, racing from one side of the planet to the other. Ships battle and lurch across tough seas where no fish—worth its salt—would ever swim. Sailing ships make good use of winds, harnessing the gusts of air to make a very effective form of propulsion. Diesel-powered ships stay on the surface for a different reason: their engines need a steady supply of oxygen to burn fuel. In theory, it should be much easier for ships to swim under the waves where the water is calmer and puts up less resistance; in practice, that creates a different set of problems.

If you've ever gone snorkeling or scuba diving, you'll know that life underwater is very different from life on the surface. It's dark and difficult to see, there's no air to breathe, and intense water pressure makes everything feel uncomfortable and claustrophobic. Submarines are ingenious bits of engineering designed to carry people safely through this very harsh environment. Although they were originally invented as military machines, and most large subs are still built for the world's navies, a few smaller subs do work as scientific research vessels. Most of these are submersibles (generally small, unpowered, one- or two-person submarines tethered to scientific research ships as they operate).

Parts of a submarine

These are some of the key parts of a typical submarine.

Pressure hull

The pressure of water pushing inward is the biggest problem for anyone who wants to go deep beneath the ocean surface. Even with scuba tanks, we can dive only so far because the immense pressure soon makes it impossible to breath. At a depth of 600m (2000ft), the maximum depth subs ever dive to, the water pressure is over 60 times greater than it is at the surface!

How do subs survive where people can't? The hull of a standard ship is the metal outside that keeps the water out. Most submarines have two hulls, one inside the other, to help them survive. The outer hull is waterproof, while the inner one (called the pressure hull) is much stronger and resistant to immense water pressure. The strongest submarines have hulls made from tough steel or titanium.

Planes

Just as sharks have fins on their bodies to help them swim and dive, so submarines have fins called diving planes or hydroplanes. They work a bit like the wings and control surfaces (swiveling flaps) on an airplane, creating an upward force called lift. Buoyancy is the tendency of something to sink, rise, or float at a certain depth. While it's underwater, a submarine is negatively buoyant, which means it tends to sink, left to its own devices, if it's not moving. But as the submarine's propellers push it forward, water rushes over the planes, creating an upward force called lift that helps it remain at a certain depth, creating a state of neutral buoyancy (floating). The planes can be tilted to change the lift force, so making the submarine climb or dive through the sea, as necessary. The planes provide most of the submarine's control of its depth, most of the time. The amount of lift they generate depends both on the angle to which they're tilted and on the submarine's speed (just as the lift that wings generate depends on a plane's speed and "angle of attack").

Ballast tanks

There are spaces in between the two hulls that can be filled with either air or water. These are called the ballast tanks and, with the diving planes, they give a sub control over its buoyancy, particularly during the first part of a dive or a return to the surface from the depths. When the ballast tanks are filled with air, the submarine rises to the surface because it has positive buoyancy. With water inside the tanks, the sub has negative buoyancy so it sinks deeper into the ocean. The tanks at the front (known as the front trim tanks) are usually filled with water or air first, so the submarine's front (bow) falls or rises before its rear (stern). The ballast tanks can also be used to help a submarine surface very quickly in an emergency.

Engine

Gasoline engines and diesel engines used by cars and trucks, and jet engines used by planes, need a supply of oxygen from the air to make them work. Things are different for submarines, which operate underwater where there is no air. Most submarines except nuclear ones have diesel-electric engines. The diesel engine operates normally when the sub is near the surface but it doesn't drive the sub's propellers directly. Instead, it powers an electricity generator that charges up huge batteries. These drive an electric motor that, in turn, powers the propellers. Once the diesel engine has fully charged the batteries, the sub can switch off its engine and go underwater, where it relies entirely on battery power.

Early military submarines used breathing tubes called snorkels to feed air to their engines from the air above the sea, but that meant they had to operate very near the surface where they were vulnerable to attack from airplanes. Most large military submarines are now nuclear-powered. Like nuclear power plants, they have small nuclear reactors and, since they need no air to operate, they can generate power to drive the electric motors and propellers whether they are on the surface or deep underwater.

Tower

Submarines are cigar-shaped so they can slip smoothly through the water, but in the very center there's a tall tower. In older submarines, the tower was packed with navigation and other equipment and was sometimes known as the conning tower (because, historically, it contained a submarines controls). It's also referred to simply as the tower or the sail, because in a modern submarine the controls and navigation equipment take up more room and tend to be located in the hull.

Navigation systems

Light doesn't travel well through water, so it gets darker and darker the deeper down you go. Most of the time, submarine pilots can't even see where they're going! Submarines have periscopes (seeing tubes that can be pushed up through the tower), but they're useful only when subs are on the surface or just beneath it. Submarines navigate using a whole range of electronic equipment. There's GPS satellite navigation, for starters, which uses space satellites to tell the submarine its position. There's also SONAR, a system similar to radar, which sends out pulses of sound into the sea and listens for echoes reflecting off the seabed or other nearby submarines. Another important navigation system onboard a submarine is known as inertial guidance. It's a way of using gyroscopes to keep track of how far the submarine has traveled, and in which direction, without referring to any outside information. Inertial guidance is accurate only for so long (10 days or so) and occasionally needs to be corrected using GPS, radar, or other data.

Life-support systems

A large military submarine has dozens of people onboard. How can they eat, sleep, and breathe, buried deep beneath the sea, in freezing cold water, for months at a time? A submarine is a completely sealed environment. The nuclear engine provides warmth and generates electricity—and the electricity powers all the life-support systems that submariners need. It makes oxygen for people to breathe using electrolysis to chemically separate molecules of water (turning H2O into H2 and O2) and it scrubs unwanted carbon dioxide from the air. Subs can even make their own drinking water from seawater using electricity to remove the salt. Trash is compacted into steel cans, which are ejected from an airlock system (a watertight exit in the hull) and dumped on the seabed.

Who invented the submarine?

Early days

• 1620: Englishman Cornelis Drebble (1572–1633) builds the first submarine by waterproofing a wooden, egg-shaped boat with leather and coating the whole thing in wax. Scientists are uncertain whether Drebble's boat ever set sail.
• 1776: During the US revolution, David Bushnell (1742–1824) builds a hand-powered one-person submarine called the Turtle to help attack British warships.
• 1800: American steam engineer Robert Fulton (1765–1815) designs a convertible ship with folding-down sails that can turn itself into a submarine for traveling underwater.
• 1863: American engineer Horace Lawson Hunley (1823–1863) develops a hand-powered submarine that ultimately becomes known as the CSS H.L. Hunley (often just "Hunley" for short). It sinks once during testing in August 1863, killing five crew, then sinks again in October 1863, killing Hunley himself and all his crew. Later retrieved, it becomes the first submarine to sink a warship (during the American Civil War)—a real milestone in submarine history.
• 1888: Spanish engineer Isaac Peral (1851–1895) builds the first electric (battery-powered) submarine. Despite successful tests, it never enters production, though Peral's ideas influence other engineers around the world.
• 1897: American inventor Simon Lake (1866–1945) launches the Argonaut, the first submarine to operate in the open sea.

Practical subs

• 1900: The US Navy launches its first ever submarine, the USS Holland, named for its Irish-American inventor John Holland (1840–1914). Although Holland had offered submarines to the Navy for years beforehand, it had originally shown no interest.
• 1908: Russia's Pochtovy is an early pioneer of Air Independent Propulsion (AIP)—operating a submarine without frequent trips to the surface—using a gasoline engine fed by compressed air.

From World Wars to the Cold War

• 1914–18: During World War I, the German navy operates a fleet of highly effective military submarines called U-boats (short for Unterseeboot, which means underwater ship). In the 1930s, the Germans start using snorkel tubes (invented by a Dutch engineer) to supply air to their U-boat's diesel-electric engines, giving them greater range and effectiveness.
• 1930s: Germany engineer Hellmuth Walter pioneers high-thrust hydrogen peroxide engines for use in submarines and missile rockets. It's another step forward for Air Independent Propulsion.
• 1952: French underwater photographer Dimitri Rebikoff launches the Poodle, the first tethered Remotely Operated Vehicle (ROV).
• 1955: The US Navy launches the USS Nautilus, the first nuclear-powered submarine.
• 1964: Alvin, a scientific research submersible operated by Woods Hole Oceanographic Institution, begins its long and distinguished history of underwater exploration. Its major successes including discovering black smokers (hydrothermal vents—a bit like chimneys in the ocean floor) and exploring the wreck of the Titanic.
• 1968: The Soviet Union (Russia and its former allies) launches K-162, the first submarine with a titanium hull and the world's fastest.
• 1969: The Soviets launch the first of their sleek, fast, titanium-hulled Alfa-class nuclear submarines.

Modern times

• 1990s: Nuclear submarines made redundant by the end of the Cold War are used for oceanographic and climate research in the Arctic in a project named Science Ice Exchange (SCICEX).
• 1990s: British-born submarine designer Graham Hawkes promises to revolutionize sub design with small, plane-like submersibles called Deep Flight that "fly" underwater.
• 1990s–: As in many other industries, China emerges as a major supplier of affordable but effective diesel-electric military submarines, including refurbished versions of the old 1960s–1980s Ming class (Type 035) and the more recent Song class (Type 039).