To fire a beam weapon at a target, you need four things:
- the beam weapon,
- power reactor(s) to charge it,
- a Beam Fire Control to aim it,
- and an Active Sensor lighting the target.
Other than the Active Sensor (which can be on a different ship), all these components must be on the same ship. Shooting at missiles is basically identical to shooting at ships, so in theory you can use any valid combination as point defense.
That said, the 80cm laser that takes 3000 seconds to recharge isn't going to knock down very many missiles.
In order to be efficient at knocking down missiles, your beam weapon system needs to account for the following factors:
- Missiles are small - you will want a resolution 1 Active Sensor in order to target them.
- Missiles are fast - you will want either a fast ship (for fixed weapons) or a fast turret to hit them.
- Missiles are fragile - you only need to do 1 point of damage to each missile, any more is wasted.
- Missiles come in swarms - you will want to fire quickly (5 second charge time) and rapidly (multiple shots per charge) if you can.
Lasers tend to have good range but poor rate of fire, and they can be mounted in turrets, which means they tend to be used as "area defense" or "secondary battery" - they don't provide the final anti-missile shots that railguns or gauss guns do. I like 15cm lasers for this, but 12cm or 10cm lasers can do just as well.
CIWS is an all-in-one point-defense component that includes everything a ship needs for point defense. In return, that's all that a CIWS can do - point defense for the ship it's mounted on. Building a point-defense system out of discrete components lets you use those components for different things - the active sensor can detect more than just "missiles hitting the ship", the gauss turret can fire at enemy ships as well, etc.