Underwater miniature drones are multipurpose tools.

   Underwater miniature drones are multipurpose tools.

"The icefin robot under the ice near McMurdo research station, operated by the US Antarctic Program. Credit: Rob Robbins USAP" (ScitechDaily.com/Icefin Underwater Robot Provides Close-Up View of Melting Beneath “Doomsday Glacier”)

New underwater drones can operate underwater even for years. The new drones can travel through ice. And they can follow animals and other interesting targets. That kind of thing makes them capable to research the whales without disturbing them. 

The only thing that limits those drones' operational time is their power source. The RTG, radioisotope thermoelectric generator, or isotope battery offers virtually unlimited operational time, even for small-size drones. The drone can use the same batteries that were created for pacemakers. And that system can give even small drones unlimited operational capacity. 

The problem with isotope batteries is if they are in the wrong hands some terrorists can use that radioactive material in their strikes. Another power source must be found so that the system is safe.  If the system cannot use the RTG it can use lithium batteries and green energy. Green energy is needed for loading those batteries. 

The system can load its batteries from submarines or surface vessels. In those versions, the system must just connect its socket to the submarine or surface unit and load its batteries. Or it can use systems that are using capillary flow to load batteries. 

The drone can have a float that can pull the tube to the surface. And then, the water flow will rotate the generator. The small-size AUVs (Autonomous Underwater Vehicles) can offer the base for quadcopters that can also operate underwater or airborne. The underwater drones can also act as drone swarms like flying drones. 

And they can use for guarding harbors and if they have acoustic or detonating systems they can make the harbor a so-called no-go zone. Or they can operate air and underwater conditions and find things like smugglers. Those drones can also search for things like military harbors and shipyards. So they are effective in recon missions. 

The system can just push its hatch through the water's surface. And send that quadcopter. Or if those quadcopters can operate underwater the system can deliver them from a long distance from the ground. The underwater drone can carry the Switchblade 600-type kamikaze drones that can give nuclear submarines more abilities than they have today. Those drones can also carry torpedoes and even cruise missiles. And those drones can operate remotely. 

Even a small drone can be dangerous for large submarines if it can make a hole in the submarine's shell. Maybe in the future. Some of those drones are equipped with laser systems. Lasers can use to make holes in the pressure hull of submarines. And those systems can offer the counter-actor for Russian "Poseidon" drones. 

https://scitechdaily.com/icefin-underwater-robot-provides-close-up-view-of-melting-beneath-doomsday-glacier/

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator