I¨ve tried two different sizes of casemat guns in the new mission Super Dreadnought or Battlecruiser. With all 8in casemat guns they make short work of any small vessel that dares come too close. The main guns keep shooting at the big ships, while the casemat guns switch to nearby threats as needed. This worked remarkably well, in my opinion.
For my second try I switched to all 7in casemat guns, but these were less effective. Despite the higher rate of fire they seemed to hit less often, and didn't necessarily blow the LC or DD out of the water when they did hit.
Going to make another run, this time with all 6in secondary armamants!