Aha, I see the confusion! Note that MLRS Turrets and MLRS are not the same thing. I see you have 25 MLRS turrets, but those are not what you unlocked (they are available from the start). The new ship type is at your space dock, and I see there are 0 out of 85 MLRS ships in service there. Build 20 of those, and you're all set!