Even $400 dollar drones would force some kind of defensive system to start shooting if the ship is to remain usable.
The ship would of course also become progressively more vulnerable as this goes on, so I don't agree that ships have some kind of D&D-style DR that means that anything costing below a million does nothing.
Surface drones are effectively indistinguishable from that threat.
Easier than avoiding torpedos, which are also long-range drones.
It's pretty hard to imagine a scenario from the nineties where there are so many speedboats in an attack that all four CIWS on a carrier use all their ammo at once. (that's an awful lot of suicidal jihadis, or whatever)
On the other hand, if the CIWS are targeting clouds of aerial drones and jetski drones at the same time, that could be a pretty bad scene. About fifteen seconds of fire per CIWS (1550 rounds), five minutes downtime to reload, between one and three seconds to service each target...
The boat swarms would close the distance fast, and the US Navy was reluctant to engage potentially stupid but non-hostile targets. By the time the threat was clear the defensive weapon systems were outside their design parameters. The alternative was killing everyone a long way out even if they weren’t a clear threat.
Not an issue today, they have loads of weapons purpose-engineered for that threat. But they had to learn that lesson the hard way.
Problem isn't a single drone, it's the cost of intercepters. Iran could launch a swarm of 100s of drones with few antiship missiles mixed in to hone in at same time. CSG has to spend $million+ interceptors and will quickly run out of them. US hasn't taken anti drone defence seriously, or the cost of doing it seriously before going in.
As far as I know we have never seen that happen against a single target. I believe the reasons are operational not cost related. A single truck can fit like 5 shaheds. For 100 at the same target at the same time you need to coordinate 20 crews just to get them in the air all these drones need to be controlled to some degree as well. It's possible but we have not seen such an attack. We have seen hundreds of drones targeting hundreds of targets against an entire country. So it's definitely possible, but I wager it's harder than it sounds to send 100s of shaheds against a carrier strike group.
Shahed drones are very slow, and can thus be very easily distinguished from antiship missiles and can also be intercepted far befpre they reach the ships. You are thinking SM-2s. But the best way to deal with such a threat is a flight of f-18s with a bunch of laser guided rockets (like 50 or 70) and a targeting pod, intercepting the drones hundreds of miles from the target.
* cost of adding encrypted mobile comms to receive target location update,
* turn about time on russian sat intell on carrier positions,
* observed carrier path patterns wrt drone flight times ( or fractions of flight time if mid air updates can occur )
* numbers and timings of drones that can be launched with alt coords to play predictive battleships with.
Unless Iran bought some CM-302 missiles from China, the mere threat of which appears to mean that China and Iran now control the oil in the gulf.
But ELI5 me maybe I don't understand realpolitik