Mostly the big problem with the huge cannon is just that there's RNG involved. Sometimes it'll hit a ship and do next to nothing to it; other times it'll hit and it's an insta-kill. It chooses it's targets randomly too, you cant manipulate it; the one and only thing you can do is keep more than one ship from being hit with a single shot, which is very easy to do... but it doesn't help you if the thing is repeatedly taking out either your HQ or other specific important ships with one blast.
And I see that Duty has two of the horrid things.
Just.... just why? WHY?
The biggest problem with them on Duty is that they can instakill your HQ. Normally the loss of your HQ isn't that of a big problem but ont hat mission it is. You loose it, you have to restart. Looks liek I have to save scum this mission, there is no other way around. Lost during 15 minutes into the mission, destroyed one of the cannons at the start, prepared to take energy mines but suddenly the second cannon oneshotted my hq and I lost.
That's nowhere fair and the thing simply shouldn't target your HQ at all.
The lack of visiual indication where it's gonna shoot is also a problem. You know when but only if you constantly check the tiny bar next to the cannon. And who has time to permanently check it any way? I'm glad these are the only two missions who have this problem but the design of the cannons wasn't very well balanced aroudn the rest of the game.
I'm also open for any useful tips for the last mission.