Drones (which are basically robots) adapt to all circumstances and applications, whether in the air, on land or underwater. And the underwater drones that first began to be used in various data capture projects have ended up being used by the naval forces to capture other types of data and carry out other activities.
One of the most advanced is the US Navy, which after many years of testing with various models of drones, is going to put one of them called the Razorback as one of its weapons for submarines.
This UUV drone (unmanned undersea vehicle) has the particularity that it can be launched into the sea through a torpedo tube, and then recovered by the same path (a torpedo tube). And what is very important, it can carry out their activities while the submarine is in motion.
.This drone is capable of autonomous operation for 24 hours over 200 miles, and capture various types of data. It has a sonar, the possibility of communicating or not with the submarine, and other unspecified sensors to preserve the confidentiality of its operations.
Using a drone of this type greatly reduces the risk of a submarine being detected by the enemy, since the drone is much smaller and it’s much more difficult to be detected.
Not only the US Navy has underwater drones, as the rest of the naval forces (China, Russia, UK, etc...) have similar weapons, what happens is that they do not advertise them excessively, and they only do so in fairly restricted environments. .
All drones (and robots in general), whatever their type, are here to stay and take on new missions, providing their operators with eyes and ears in far away places, and reducing the risks for some people. Always in favor of those with more technology.
This trend will continue, and they will be provided with more technologies (AI and others) to be increasingly autonomous and capable.
I just hope the future ability to kill isn't left to be decided by a machine.
A video can be seen at: https://www.youtube.com/watch?v=-V3o_Kd6xWo
EN 
ES_ES 