Does GPS work underwater for submarines? --- John, Huntington Beach, Calif.
Marshall Brain answered:
Fun fact: I used to live in Huntington Beach when I was a kid, on Spindrift Lane.
If you read How GPS Receivers Work, you realize that GPS signals are fairly weak. They are coming from satellites orbiting at 11,000 miles. By the time the signals get to earth, they are so weak that even heavy tree foliage can block them.
Therefore, the only way for a submarine to use GPS signals is to come to the surface or to tow a buoy that is floating on the surface. There is no way for GPS signals to penetrate the water.
So how do submarines navigate when they are underwater? The most important tool is the inertial navigation system. An INS uses precise accelerometers and gyroscopes to keep track of every change in the submarine's speed and direction. A computer monitors all the changes and therefore knows where the submarine is. Obviously over time small errors add up, so the submarine will come to the surface periodically to get a GPS reading and recalibrate the system from a known point.
For more info see: How Submarines Work
PS - Back in World War II say, before inertial navigation systems, submarines could not stay down for very long anyway. Navigation was done just like it would have been done in a ship, using charts, compass+clock, stars and landmarks. You can see the basic controls in a German WWII sub is this video:
[[[CLICK HERE for answers to thousands of questions by Marshall Brain]]]