I rip on surface fleets as being floating reef fodder that would be sunk almost immediately against any modern power, either because of the sophistication of submarines, the rise of cheap drones winning the economic exchange, or death-from-above missles and ICBMs that are basically undefendable.
But against subs I'm surprised there aren't plans for a drone-net that surrounds a fleet or high value ship that can detect incoming underwater threats via some mesh networking.
Smaller drones have weaker propulsion and can't keep up with the ship its supposed to provide a detection bubble around. Being underwater and having to deal with additional drag also doesn't help. The large size of an aircraft carrier belies the fact that it is the fastest ship in the carrier group and can outrun all of its escorts. Larger ship = more space to pack powerful engines.
That's also a major issue for a lot of other drone swarm schemes such as using drone swarms to counter fighter aircraft. Smaller drones don't have the propulsion to keep up with fighters, and once you make drones large enough to hold the engines that would let them keep up with a fighter you might as well build a fighter instead.
Agree that power is the biggest limitation on drone/swarm concepts. Small engines / rotors are just not as efficient.
It is interesting to consider the change in tactics and design once you consider the fighter expendable. You don't have to turn away once you get shot at in-range -- you can keep flying and shoot at the point of maximum impact. The aircraft might only be designed to last for 10 combat hours, or to have a poor safety record. For example, in aircraft the design margin is ~1.5 (vs >2 for surface); for unmanned it might be ~1.1.
The drone-vs-human tactics will persist until both sides have competent drones, at which point they might evolve to look more like human-vs-human tactics: protect your high value assets, imperil theirs.
There were networks of deployable remote surveillance buoys being developed by the 1990s. Source: Public research reports of military research organizations. Presumably removing the propulsion expectation simplifies the problem domain.
I wonder if you could have a flotilla of heli-drones that drop in sampling microphones/active sonar. Wind might be hard to deal with in storms or heck even typical conditions.
A typical ship is going to be out at sea for a long longer than an hour. A drone-net that only lasts for an hour isn't exactly a persistent detection zone. If you want something with range + speed, you're going to need size for the power plant and fuel. Maybe you could hack together something with drones coming back to a mothership to recharge.
If by fighter you mean "manned fighter" there are several reasons to build large, fast drones; no life support overhead, much better maneuverability (tolerance for high g), no worries about pilots flying highly dangerous missions, can use impact kills.
But against subs I'm surprised there aren't plans for a drone-net that surrounds a fleet or high value ship that can detect incoming underwater threats via some mesh networking.