The advice is, if you find anything suspicious such as those illustrated in these images.
Dial 999 and ask for the coastguard; report what you have seen & where it is
[one of the few times when I think "what three words" would be most useful].
Whatever you do, DO NOT touch it - stuff from WW2 is likely to be very unstable ...
Let the experts deal with it.
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Not my Image : fair use & public education