The pitch change in WW2 sonars could come from ship turning toward you. Because of Dopler effect you should get slight, but audible pitch change of the pings. And since most ships were using mine to kill, they had to go toward you.
Dopler does not work on active pings in DW. You always get for example 7500 Hz. Sometimes it seems there is some Dopler effect on passive NB lines. At least for circling torpedes some lines moves .. but some dont .. they should move all.
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