How do submarines navigate? Submarines navigate using a mix of sonar, inertial navigation systems, and GPS.
There are a lot of naval and civilian submarines in the world. The number of civilian submarines would probably be easier to work out than the number of military ones because most countries keep that number a secret. Or, they release information on how many old submarines they have, which is probably already public knowledge, but keep the number of new ones they have a secret. That makes sense because you don’t want to give your enemies fair warning of what submarines you are building. That being said, there are lists online, which may be reasonably close. That puts Russia and the US in joint first place with between 65 and 70 submarines each. Then comes China and, rather worryingly, North Korea is in fourth place with 35 submarines. North Korea has created nuclear weapons and wants to have a strong navy to provide a base to fire these missiles, rather than trying to feed their starving population.
Modern nuclear-powered submarines could stay at sea forever if it wasn’t for the people on board who need supplying and changing. They can also stay underwater for months at a time because they can make oxygen from the seawater. So, how do they navigate in the deep dark sea?
They do have GPS navigation, which can show them where they are on Earth by triangulating their position between three satellites. The problem is, the radio waves the GPS uses to work out where something is cannot penetrate water. Radio waves just bounce off water and head back into space. That means, GPS is only useful when the submarine has surfaced, and so is not much use as a navigation system.
Underwater, submarines make use of an inertial navigation system and of sonar. An inertial navigation system is a good way of working out movement and modern smartphones have tiny versions inside of them. That is how your phone is able to count your steps. An inertial navigation system used to be analog, but these days they are digital. They consist of three accelerometers and three gyroscopes. The accelerometers can work out the speed of the vessel and the gyroscopes can work out how quickly the submarine is turning. There are usually three of them, but there can be more. There have to be at least three of them because all submarines can move in any direction. The accelerometers and gyroscopes are on the X, Y, and Z axis. They feed information to a computer, which can then calculate where they are. It does this by knowing the starting point and calculating speeds and how much and how fast they have turned along the way. The inertial navigation system is good, but it is only accurate to 150 hours. Small errors can creep in and there can be some uncertainty in where they are. The system has to be realigned by using GPS. The submarine will either have to surface or come close enough to the surface to put up an antenna.
Submarines also use sonar to navigate. This isn’t much use in completely open sea, but it is useful when close to the seabed, objects, or other ships. Sonar works by sending out a sound wave and then calculating how long it takes to come back. By knowing the speed of sound in water, the onboard computer can work out how far objects are. It doesn’t work in the open sea because there is nothing for the sound wave to bounce off. One of the problems with sonar is that other submarines will be able to hear it. Submarines monitor for their own sonar, but they also have passive sonar, which is always listening for sounds in the sea. It will easily pick up the sound of another submarine’s sonar and give away its position.
Submarines also use magnetometers and pressure sensors to navigate. The Earth has magnetic fields and by measuring these, the submarine can have some idea of where it is. A lot of animals also use these to steer and to navigate long distances. The pressure sensors tell the submarine its depth. As the pressure increases, the submarine is getting deeper. By combining all of these systems, the onboard computer for a submarine can work out pretty accurately where on Earth the submarine is and navigate it safely. And this is what I learned today.
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Sources
https://en.wikipedia.org/wiki/Submarine_navigation
https://science.howstuffworks.com/transport/engines-equipment/submarine4.htm
https://www.advancednavigation.com/tech-articles/inertial-navigation-systems-ins-an-introduction
https://worldpopulationreview.com/country-rankings/submarines-by-country
https://www.nti.org/analysis/articles/north-korea-submarine-capabilities
Photo by Vitali Adutskevich: https://www.pexels.com/photo/submarine-in-the-harbor-14754974/