Ideas for drone swarms
1) Anti-missile drones for the navy. In event of missile attack on a ship, the warship deploys a swarm of thousands of A.I controlled drones that act as a protective cover for the ship, they calculate the trajectory of a missile and positions themselves in the path of the missile. Missile rams into the drones and explodes before hitting the ship. Intended as last line of defense. I imagine that you can make a underwater version that works on torpedoes too.
2) Drone swarms carried by "carrier missiles" to be used to soften enemy warships. The "carrier missile" carries the FPV swarm within 4-5km of the target, unleashes the swarm and the drone swarm proceeds to target systems like the CIWS and radar arrays. Basically it's just a way of softening up a target and degrading their anti-missile capabilities before the main wave of missiles.
3) A similar version of number 2, a missile carrying many submunitions or drones, the key difference is that this are meant to be launch slightly ahead or during the main missile wave and are primarily meant to act as decoys and to confuse/overwhelm an enemy's missile defense system, not to meant direct damage.