Great, thank you all very much for your answers. Yes I meant how deep do you have to dive to escape from ASDIC. But I think this will change with the years and I have to dive deeper and deeper.
But good point with the measuring the depth: Will this always be heard of the destroyers when in range or only when they are alertet? And how far is the range? Sure I can find it out slowly ingame but a rough estimate again is always helpful