If someone had the technology to make a drone able to dive 3.7km to the bottom of the ocean, had enough strength to bring back a rock and then propel itself 40m

If someone had the technology to make a drone able to dive 3.7km to the bottom of the ocean, had enough strength to bring back a rock and then propel itself 40m above the surface and keep that small, your scenario would be the least of my worry. Anyway, if you are in position to bring something close to a carrier from underwater, an heavy torpedo will do the job for a lot less money that your swarm.