[sbierwagen]

The land-based version of CIWS is called Centurion: https://en.wikipedia.org/wiki/Phalanx_CIWS#Centurion_C-RAM

C-RAM shells are supposed to self-destruct, but EOD guys will tell you that fuzes do not have a 100% operational rate. Another problem is cost and magazine size:

>The Block 1A and newer (pneumatic driven) CIWS mounts fire at a rate of 4,500 rounds per minute with a 1,550-round magazine.

>Shells fired by the Phalanx cost around $30 each and the gun typically fires 100 or more when engaging a target.[14]

So it's about three grand to zap one drone, and you get 15 shootdowns before a human needs to shovel more ammo into the turret. That would make it vulnerable to a saturation attack. A hundred drones carrying grenades that home in on the CIWS radar would be tough to counter.