How Do Submarines Work? Engineering Under the Sea

Submarines are some of the most extraordinary machines ever built — designed to dive deep below the ocean’s surface, survive crushing pressures, and move silently through complete darkness.

But how do these massive metal vessels manage to sink, float, and travel underwater for weeks at a time?
The answer lies in clever mechanical engineering, physics, and a deep understanding of buoyancy and pressure.

Let’s dive in (pun intended) and explore the fascinating world of submarine engineering.

The Science Behind Submarines

At their core, submarines rely on one fundamental physical principle: Archimedes’ Principle — which states that any object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces.

This principle determines whether a submarine floats, sinks, or stays suspended underwater.

To control buoyancy, submarines use ballast tanks — large compartments that can be filled with water or air.

When tanks are filled with water, the submarine becomes heavier than the water it displaces and sinks.
When tanks are filled with air, it becomes lighter and floats.
To hover at a specific depth, engineers precisely balance the amount of water and air inside the tanks.

A submarine doesn’t “push” itself underwater — it simply changes its density to dive or rise.

How Submarines Dive and Surface

Submarines have two main types of ballast tanks:

Main ballast tanks (MBTs): Used for large buoyancy changes — diving and surfacing.
Trim tanks: Used for fine-tuning balance and stability.

To Dive

Valves open, allowing seawater into the ballast tanks.
The air inside is vented out.
As the submarine becomes denser than the surrounding water, it sinks.

To Surface

Compressed air is blown into the ballast tanks.
The air pushes out the seawater.
The submarine becomes lighter and rises.

This precise control lets submarines dive hundreds of meters below the surface smoothly and safely.

Pressure: The Hidden Enemy

As submarines go deeper, water pressure increases dramatically — roughly one atmosphere (14.7 psi) for every 10 meters of depth.

To survive this, submarines are built with:

Pressure hulls: thick steel or titanium cylinders designed to withstand immense pressure.
Spherical ends: a rounded shape distributes pressure evenly, reducing stress points.
Watertight compartments: to prevent catastrophic flooding if one section is breached.

For example, modern military submarines can dive to depths of 300–600 meters, while specialized research subs have reached more than 10,000 meters in the Mariana Trench.

The deeper a submarine goes, the more it becomes a battle between engineering strength and the power of the ocean.

Propulsion: Moving Through Water

Unlike ships, submarines move through a dense, drag-heavy environment.
To do this efficiently, they use streamlined hulls and powerful propellers (screws) designed to minimize turbulence and noise.

Propulsion Systems

Diesel-electric submarines: Use diesel engines at the surface and battery power underwater.
Nuclear submarines: Use onboard reactors to generate heat, powering turbines that drive the propellers — allowing them to stay submerged for months.

Modern subs also use pump-jet propulsion — which works like a jet engine for water — offering quieter, more efficient movement, essential for stealth.

Life Support Underwater

Life underwater isn’t just about propulsion — it’s about survival.

Submarines must create a livable environment deep below the surface by managing:

Oxygen: Generated through electrolysis (splitting water into hydrogen and oxygen).
Carbon dioxide: Removed by chemical scrubbers.
Fresh water: Produced by desalinating seawater.
Temperature and humidity: Controlled by HVAC systems adapted for closed environments.

A submarine is essentially a self-contained ecosystem — an underwater city powered by engineering.

Navigation and Communication

Without GPS or sunlight, submarines rely on advanced systems to know where they are.

Inertial navigation systems (INS): Track position using gyroscopes and accelerometers.
Sonar (Sound Navigation and Ranging): Uses sound waves to detect obstacles, other vessels, and ocean floor features.
Periscopes and photonic masts: Allow viewing above the surface without surfacing.

For communication, submarines use very low frequency (VLF) or extremely low frequency (ELF) radio waves, which can penetrate seawater — though at low data rates.

Applications Beyond the Military

While most people associate submarines with naval warfare, their technology serves many peaceful purposes:

Research submarines explore deep-sea ecosystems and geology.
Tourist submarines allow civilians to explore coral reefs and marine life.
Rescue subs assist in emergencies at sea.
Autonomous underwater vehicles (AUVs) perform mapping, surveillance, and resource exploration.

Each type represents a different engineering challenge — from life support to autonomy.

The Future of Submarine Engineering

The next generation of submarines will be smarter, quieter, and more sustainable.

Engineers are working on:

AI-assisted navigation for autonomous underwater missions.
Advanced composite materials for stronger, lighter hulls.
Hybrid-electric propulsion systems to reduce noise and improve stealth.
Underwater drones that can operate in swarms for exploration and defense.

The ocean remains one of the last frontiers on Earth — and submarines are the machines that let us reach it.

Conclusion

Submarines are a triumph of mechanical and marine engineering — balancing forces, pressure, and life support in one of the harshest environments on the planet.

Every dive is a demonstration of physics in motion: density, pressure, propulsion, and precision working together to explore the deep.

From nuclear submarines to research vessels, these underwater giants remind us that the limits of engineering don’t end at the surface — they extend far below it.

GearUp Engineering

How Do Submarines Work? Engineering Under the Sea

The Science Behind Submarines