Fourier Transform in Submarines

Submarines (especially the first and early version ones) use a hydrophone, which is basically a microphone to collect sound waves underwater. And just like a regular microphone there could be all sorts of sounds and noise that you could collect. The tricky part now is to be able to filter the electrical signal output of the hydrophone in order to only listen to the sounds you want to listen to. This is especially important during battle whenever the submarine looks for enemy ships. In order to focus-in to the particular signal you are looking for, the electrical signal from the hydrophone is usually passed into several filters in order to single-out the certain frequency you want to hear (usually there are certain frequencies for each ship or submarine). The mathematical process for this analysis is the Fourier Transform and with the help of the early computers, they have used the Fast Fourier Transform algorithm in order to speed up the process.

References:
https://cadcammodelling.wordpress.com/2011/04/14/fourier-transform-and-its-applications/
https://fas.org/nuke/guide/usa/slbm/ssbn-secure.htm
US Nuclear Submarines: The Fast Attack by Jim Christley https://books.google.com.ph/books?id=N1ibCwAAQBAJ&pg=PA2&source=gbs_toc_r&cad=4#v=onepage&q&f=false

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