How Submarines Work


Submerging and Surfacing

A Submarine can float on water because the weight of the water displaced is equal to the weight of the craft. The upward force that the water has on the vessel is known as they buoyant force. The key to controlling a submarine’s diving and resurfacing, is to control the buoyancy.

Submarines are equipped with ballast tanks and trip tanks that can be filled with either water or air. To have the submarine sitting on the surface, the ballast tanks must be empty; to descend, the air in the tanks is replaced with water. The density of a submarine then becomes greater than the water and it will submerge. There is a supply of compressed air on board that is used for both life support and to fill the ballast tanks.

The speed of descent is additionally helped with a set of diving planes or “wings” on the top of the submarine. The angle of the wings is controlled, thus influencing the angle of descent.

To keep the submarine level at any depth, the submarine maintains a balance of air and water in the trip tanks, so that the overall density is equal to the surrounding water. The diving planes also help keep the depth of the submarine constant. The rudder on the back of the craft helps steer it.


Power Supply

Nuclear submarines use nuclear reactors, steam turbines, and reduction gearing to drive the main propeller shaft. Electric power is also used to operate equipment, this is made from diesel engines and nuclear reactors. Batteries may also be used for electric power, and they may be charged using either a diesel engine or a nuclear reactor.

Nuclear submarines have an advantage to diesel submarines because they can stay submerged for weeks at a time. Diesel engines can only be used while the submarine is surfaced, or at least using a snorkel, to recharge the batteries. Once the batteries are charged, the submarine can descend using electric power. Because nuclear fuel lasts much longer than diesel fuel, nuclear submarines can stay under water or at sea for long periods of time, without having to port to refuel.


Submarines navigate using global positioning system while on the surface, however, this will not work while the vessel is submerged. Underwater, the crafts use inertial guidance systems that keep track of the ship’s motion from a fixed starting point using gyroscopes. These systems are very complex and difficult to use, and very accurate at the same time. They are accurate up to 150 hours at a time.
To locate targets, submarines use passive sonar. This works by emitting sound waves through water and allowing the sound waves to reflect off the target and return; by knowing the speed of sound in water and the time it took for the sound wave to travel back, submarines can calculate the distance to the target. This is the same technique that bats, dolphins, and whales use. These systems can also help recalibrate the inertial guidance systems.

Air Supply

Oxygen is supplied from either compressed tanks, or an oxygen generator, which works by electrolysis. Oxygen can either be released in periods throughout the day, or whenever a computer senses the oxygen level is low. Carbon Dioxide must be removed from the air as well. This can be done chemically using soda lime in “scrubbers”. The carbon dioxide is trapped and removed from the air in chemical reactions. Moisture is removed by a dehumidifier, this prevents condensation buildup within the ship.

Water Supply

Most submarines can take in seawater and turn it into fresh water through a distillation process. The distillation plant on submarines can produce 10,000 to 40,000 gallons of water per day. The water is mainly used for cooling equipment and for the crews’ personal use.


Intro Page History Uses How They Work Sources