How Submarines Work

A submarine is not just a ship that can go underwater. It is a closed survival system that can control buoyancy, resist water pressure, move quietly, navigate in darkness, and detect the world through sound.

The first key idea is buoyancy control.

Any object in water experiences an upward force called buoyancy. A normal ship floats because it displaces enough water to support its weight. A submarine can float too, but it has one special advantage: it can change its weight.

This is done with ballast tanks.

When a submarine wants to dive, valves open and seawater enters the ballast tanks. The submarine becomes heavier, and it begins to sink. When it wants to surface, compressed air pushes the seawater out of the tanks. The submarine becomes lighter, and buoyancy lifts it back toward the surface.

But a submarine does not simply sink or rise. It must control its depth smoothly.

For this, it uses hydroplanes, which work a little like the control surfaces on an airplane. When the submarine moves forward, the hydroplanes adjust the flow of water and help the vessel rise, dive, or stay at a chosen depth. The submarine can also adjust its internal trim tanks to balance weight between the front and rear, keeping the hull level.

The second key challenge is water pressure.

The deeper a submarine goes, the greater the pressure becomes. Roughly every 10 meters of depth adds about one atmosphere of pressure. At great depth, seawater squeezes the submarine from every direction.

The structure that protects the crew is called the pressure hull.

This is the strong inner shell that holds air, people, and equipment. It is usually cylindrical or rounded because curved shapes distribute pressure more evenly. The outer shape of the submarine may look smooth and streamlined, but the pressure hull inside is the real protective shell.

The third key technology is sonar.

Light does not travel far underwater, and radar does not work well because electromagnetic waves weaken quickly in seawater. So submarines mainly use sound.

There are two main types of sonar: active sonar and passive sonar.

Active sonar sends out sound pulses and listens for echoes. It is useful for detecting objects, but it also reveals the submarine’s presence.

Passive sonar is quieter. It does not send out sound. It only listens. It can detect propellers, engines, pumps, and other underwater noises. Modern submarines may use bow sonar, side sonar, and long towed sonar arrays to listen across large distances.

This leads to one of the most important submarine abilities: silence.

Underwater, sound can travel very far. A noisy submarine is easier to detect. That is why modern submarines are designed to reduce vibration and mechanical noise. Engines, pumps, pipes, and moving parts are isolated to prevent sound from spreading into the hull.

The propeller or pump-jet is also carefully designed to reduce cavitation.