In the Star Wars Universe, Ion Cannons are useful for disabling a ships systems and shields without destroying it. In Star Wars: Armada, they are a great way to set your opponent up for destruction .
Found in: CR-90
The Good: Rerolls are a good thing and can be pretty hard to come by. Being able to gain them on every attack is really useful.
The Bad: They require spending a blue die, and blue dice will never have a blank for you to spend.
Best on: The Victory-II or any other ship that combines blue dice with lots of red and black.
Combos with: Enhanced Armament or other upgrades that red or black dice.
Verdict: This is a good upgrade for the price. It really only is worth using when you roll more than 1 blank. 4 points isn't too much to pay for an insurance policy against really bad rolls.
Ion Cannon Batteries
Found in: Victory SD
The Good: Currently the only way in the game to deny your opponent command tokens. When it doesn't work it kicks in an extra point of damage.
The Bad: It can be useless if your target has neither shields or command tokens.
Best on: I like it on the CR-90B. It gives the ship a little more punch for a reasonable cost.
Combos with: Tractor Beams! Take away any banked Nav tokens to make sure that the Tractor Beams do their thing.
Verdict: This was a card I initially dismissed, but have come around to really liking. It is important to pay attention to when the damage kicks in if there are no tokens. It happens before the rest of the damage and cannot be mitigated by defense tokens.
Found in: Core Set. Victory SD
The Good: Exhausting all of your opponents defense tokens can set them up for some hard choices later in the turn.
The Bad: You really have to use it early in the turn to get much out of it.
Best on: This is probably best on the CR-90B. If you go first you can move it into position late in the round, go for the Overload Pulse at the beginning of the next round and then run like crazy.
Combos with: Admiral Screed can get you the Crit you need to get the effect off.
Verdict: This is one of those cards that can be really powerful. In practice I've often had trouble getting it to work as well on the table as it should in my head. When I have everything setup right to cripple a ship for later pummeling I don't roll the crit needed to trigger the effect. When I do roll the crit, the follow up shots are often out of position. This upgrade will probably be more effective t 400 point games where there will be more follow up shots to take advantage of the overloaded enemy ship.