I"m not sure, unless Duc redid mines, but I believe most mines are set to get you at periscope depth.
Planes are possible.
You implied you always die, repeating the same thing. Doe's this only happen under the circumstances you listed. It should be very rare to die by plane or mine at that depth, if at all.
Give us more info. Is everything running fine when you leave port, where is this happening, ect.
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