The Corrosion Resistant Aerial Covert Unmanned Nautical System -- CRACUNS for short -- is a high-tech underwater drone that is also fully capable of making flights above the surface as and when required.
Developed by a team of engineers at the Johns Hopkins University Applied Physics Laboratory, this craft is capable of being submerged in salt water for up to two months at a time without suffering any lapses in function. When called to use, it can uncouple from its underwater base and float up with the help of its propellers, before taking off into the air.
Despite this high-tech functioning, the CRACUNS drone is relatively inexpensive to manufacture. This makes it ideal for use in high-risk military and industrial scenarios where there's a real risk of losing the drone.