CIWS Firing rules:
To attempt to hit a missile weapon target add +3 difficulty to the standard range difficulty. If roll equals difficulty, target is severly damaged and moves one hex (30,000m) in a random direction. Role 1d6 to determine direction (1-forward, 2=forward right of original direction of travel, 3=backward right of original direction of travel, etc.). Target then detonates in that hex.
If roll is +1 greater then difficulty, target detonates in hex where hit doing 1/2 damage then normal. If role is +2 (or more) greater then difficulty target is destroyed and does not detonate.
And here is the spacedock purchase capability:
CIWS Firing Mode
SU Cost: 2
Energy Cost: 1 Power/use/round
Purchasing the CIWS firing mode capability installs a small independed latteral sensor that is only capable of tracking an assigned target. This allows for the ability to track smaller incoming ordinances. This may only be purchased for beam weapons, microtorpedo launchers, and rocket launchers.