Underwater Drones ???

The difficulty with autonomous submarines is that, in contrast with other robotic applications, their sensors will not be able to give them sufficient information to make an informed decision. Specifically, if the submarine were to encounter a ship that is transporting enemy supplies, there would be no way for the submarine to know how many civilians are on board. Without that knowledge, it would not be allowed to sink the ship for fear of killing too many innocents.

You can read the rest @
https://en.wikipedia.org/wiki/Unmanned_underwater_vehicle

Neither a manned submarine nor an UUV can tell how many "innocents" are on board a ship.

Here are the real life rules of engagement for submarines:

• Find the enemy's ships,
• Sink them, and
• Don't worry about the innocents.