So - to my mind, my prime goal was to improve a cruisers air defence - not only this but if the cruiser was submerged a combat sub could surface and fire on targets, especially air targets, without risking or even revealing the presence of the parent ship. The A4 launcher seemed like a great choice as it offered great range, could fit on a light vee and offered artillery support too - again, allowing artillery support without revealing the parent craft - or any large naval target. So, the sub was conceived to be able to appear, blow things up a long way away and disappear off into the depths. The speed is bad, the defensive weapons are bad - there's not a lot of weight left after an A4 and armour - but it fulfils that primary role and other units can cover for the other weaknesses. Serious anti air can be done by fighters from the heli pad or sub caps off the cruiser but a few missiles without bringing the cruiser into view is the main point
Fitting a light vehicle bay would be a big plus, the planned cruiser isn't statted yet but primarily supports light vehicles - I'm going to have a play around and see if a heavy sub might give better performance (still 1 A4 but also some LRT and maybe some more speed) - however, I really like the idea from Fireangel of loading it into a heavy vehicle - suddenly I want to build a heavy WIGE (flotation hull as standard) with a light vee bay. As part of the cruisers vehicle compliment this would be able to "hurry up" any of the light vee, carry them across impassable terrain, make quick visits to resupply depots etc.
