Plasma weapons are perfectly useful, just as the other weapons in CBmod are, but they're less immediately apparent.
1) They use
no supply whatsoever.
2) They fire every turn.
3) Their costs make them extremely useful for balancing costs in large fleets, reducing build time and maintenance.
4) They have a large 'punch'.
The first point is fairly obvious in its meaning and benefits. Ships with energy weapons can continue fighting long past the limits of kinetic-armed ships, and they can devote all of their supply storage to engines. They have longer operational range and time than their kinetic kin. Especially if you plan to share supplies between ships and you have missile ships (which chew up supplies like there's no tomorrow), this is an important aspect to pay attention to.
Firing every turn is an enormous benefit in close-quarters combat and in large-scale operations. Ships on the front line will take lots of damage and they can't move around much, so they have to shoot at point-blank range into the enemy right next to them. You might find it interesting to put ships like
this one in your simulator and watch how efficiently those twin cannon chew up ships. Short-range DF weapons are far superior to long-range DF weapons for massive battles.
Point 3 is extremely important to note. Everyone knows how horrible Stock SE4 is on this subject - everything is minerals. Life is minerals. If you are unlucky enough to start in an area without many minerals, you're going to die. Ships cost ridiculously high quantities of minerals to build and maintain. Energy weapons require radioactives almost exclusively, making them very useful for balancing firepower and cost from the scale of the individual ship to the scale of the 500-ship fleet. You won't be able to build as many as you can if the kinetics, but they'll keep your minerals cost down and make sure you can use your spaceyards with a lot more efficiency. Stock shipyards spend about 80% or more of their time sucking up minerals but they often build the orgs and rads in the first turn of construction. Keeping ship costs balanced means you can make better use of your colonies' resource amounts, can maintain your ships more effectively, and perhaps most importantly, build very powerful ships much faster.
This brings us to perhaps the deciding factor - damage. Leaky shields are very interesting in their effect of draining damage from each shot. I'm sure you're all aware of how futile it is to launch 50 20mm DUC shells at a ship with even 20 shield points. You're going to get 2 shots through to the hull. As the damage absorbtion on the target increases, so does the amount of 'punch' (damage per shot) required to break through the shielding and inflict damage that can be felt to the underlying hull. Let's examine the options...
Torpedo weapons - long range, massive damage that *increases* as range increases, long reload time (3). These weapons are the heaviest guns you can find, easily. But... they have hefty size requirements, and even their longer range won't be useful when the entire battle map is clogged up with 400 combat ships and literally thousands of fighters. Plus, they fire once and then they're useless for 3 turns. On the plus side, you can't put enough shields on a ship to protect it from a torpedo hit.
Beam weapons - long range, very high damage that trails off as range increases, medium reload time (2). Masers, Lasers, X-Ray lasers, GRasers, these guns do huge amounts of damage when they hit, and even the heaviest of shielding is well-nigh useless against them. However, they have an incredibly high cost in Rads, and they suffer from the same reload time problem that torpedo ships suffer from.
Projectile weapons - short range, good damage, negligible reload time. Projectile weapons have the best damage/turn/kt ratio of all the weapons in CBmod, and if they can get within range of the enemy, they'll slice through enemy ships like a tablesaw through... well, anything, really... the main disadvantage of projectile weapons is against ships with very heavy leaky shielding. Since even the 100mm ones do ~120-150 (not sure of the actual entire range here) per hit, if a high-tech ship with around 60-80 points of shielding goes up against a DUC ship, the armor will not have to absorb much damage to keep the ship fighting and alive.
Plasma weapons - the focus of this article. Plasma weapons are *almost* twice the damage of projectile, twice the size, and have slightly less cost than the beam weapons. It is important to note that on their own they are a very good mix of beam and projectile weapons. However, the trick here is the
punch - while the extremely important ratio of (damage / turn / kT) isn't quite as good as the projectile weapons, they do a lot more damage *per shot*. This is important:
Consider a ship with 80 points of leaky shielding. We'll pit it against two potential designs in the safety of our minds. Each ship will spend 50 kT on weapons.
Design 1 features twin 100mm Depleted Uranium Cannon IIIs (114 damage each, up to 3 range). It will do 228 damage each turn to the enemy. However, due to the way leaky shielding works, each shot will lose 80 points of damage, thus, we'll get each shot doing 34 damage on average, for a turn total of 68. A lot worse than 228, no? Also, this will use up 100 supplies a turn...
Weapons cost: 1500, 0, 250
Damage lost to shielding: 70%
Design 2 features a single 100mm Plasma Cannon III, doing 209 damage to 3 range. It will similarly lose 80 points of damage per shot to the shields, but, since the damage is so much higher, it will be doing 129 damage a turn average.
Weapons cost: 250, 0, 4800
Damage lost to shielding: 38%
There is no denying that the plasma cannon is significantly more expensive, but note the difference in combat prowess. Design 1 has to make 4 times the number of shots in twice as many turns to pull off the same amount of damage to the hull as Design 2. In this time, enemy ships will be shooting at it, it might miss, it is blocking space that other ships need for moving around in...
Just imagine that the shielded target has some armor. 34 damage a shot is just enough to take out a single 20cm armor component of Tritanium. Another tech level up, and your projectile cannon can't even knock out 20cm armor. The only way it could do much damage would be to score a very low-probability lucky hit against a shield generator and reduce the shielding, whereas the plasma ship will be slicing out chunks of the hull with a vengeance.
Against heavily shielded enemies, plasma is clearly superior. Against enemies without much shielding - and for general purpose construction, due to cost - projectile is clearly superior. This is the beauty of CarrierBattles Mod. Everything is balanced very, very well.
Hope this helps