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The Scientists at John Hopkins have developed a Quadcopter drone that can stay under saltwater for two months and still fly! This monster is called CRACUNS and can be launched from 60 m depth.

It will probably not be very operational under water but it can be launched from there or hide there.
Have a look at this video:



More here

Used real Carbon Fibre; you can see the wrinkles on the fabric. Trying to bag and cure it with those contours is not easy; interesting build.

Yes I want one