Talk:I-58/@comment-36.75.21.239-20140313120353/@comment-50.103.232.35-20140326021857

usually submarines of the WWII era came equipped with hydrophones which are a type of passive sonar which pick up any sounds generated in the water, such as the sound of the turning of a ships propellers. Later in the war subs began equipping active sonar(also sometimes known as ASDIC)which projects a sound into the water which bounces off any object in the water and returns back to a receiver which then calculates the distance of said object based on the time it takes the sound to return to the receiver.