In the deployment screen for campaign missions after the first, you can drag the grayed-out portrait of an already-added ship to add a duplicate ship to your deployment. These ships are remembered for subsequent missions.
Ultimately, I didn’t need the exploit since I flawlessly crushed everything with Kraugerisk armored missile dreadnaughts… but it’s still something that needs fixed.
Yikes, thats an oversight 
I shall fix this immediately…thanks for pointing it out. Did you generally find the campaign too easy then?
Well, I was able to get away with spamming nothing but an armored Sabre dreadnaught with 3 tracking arrays and an assortment of torpedoes, MWMs, and fast missiles. Its tracking was so good it could readily shoot down fighters without needing any tractor beams, and none of them ever went below 90% armor throughout the entire campaign - opposing ships tended to get shredded shortly after they came into range.
Not sure how much of that is the campaign being too easy and how much is the Sabre’s tracking bonus being really powerful.
I was able to waltz through with nothing but some general purpose dreadnaughts. In some missions, just two or three of them. Was the campaign supposed to have a 100,000 limit?