The worst thing that could ever happen to you on a ship in the middle of the ocean would be for water to flood in and make you sink to the seabed. But if you’re on-board a submarine, that’s exactly what you want! Unlike ships, which pitch and roll as they struggle across the waves, submarines slip swiftly and silently through the calmer waters beneath. They are lean, mean, military machines and they can stay submerged for weeks or even months at a time. Let’s take a closer look at how they work!
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).
These are some of the key parts of a typical submarine.
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.
There are spaces in between the two hulls that can be filled with either air or water. These are called the ballast tanks. When they are filled with air, the submarine rises to the surface; with water inside the tanks, the sub sinks towards the seabed. By changing the amount of water or air in the tanks, the submarine alters its buoyancy (ability to float) so it can move close to the surface or deeper down. 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).
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.
Submarines are cigar-shaped so they can slip smoothly through the water. But in the very center, there’s a tall tower packed with navigation and other equipment. 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.
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. As the sub’s propellers push it forward, water rushes over the planes, creating an upward or downward force that helps the sub gradually rise or fall. The fins can be tilted to change the angle at which it climbs or dives through the sea.
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.
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.