Why, turrets didn't work the first time. This is why the FDT fluff made a degree of sense as it was an attempt to improve existing defenses rather then heap on more of the same. Remember that 'turrets' is a catch all for dozens of different weapons systems, basically an abstraction to make the game simpler. Logically, since the existing systems did little to help, they'd look into something new.
Background
I don't think that this fleet list represents battlefleet Bakka “Today†(999.M41). The presence of the Dominus Astra and Admiral Rath implies that the list represents battlefleet Bakka before or during the first tyranic war (~745.M41). So the “improved†turrets are no reaction to the tyranid menace, it is the tactical setup of Bakka ever since. Even if we assume that this list is from the “40k present timeâ€, there are a lot of arguments against such a change.
a) The tyranids are “just another alien raceâ€. We, the players know that they are something bigger, but from an ingame view they are “joe alienâ€: a race like a hundred other which the Imperium had annihilated during its existence. Keep in mind that after the battles of Circe/Macragge the Imperium believed that they had defeated the tyranids once and for all. Only after the apperance of Kraken (993.M41) and Leviathan (997.M41) they realised that there are many more of them. And you don't change your tacics against a opponent if you thing he is beaten already.
b) Imperials don't change their setups so easily. The templates are holy and sacred for the mechanicus. The Black Templars needed over hundred years that the Land Raider crusader was accepted by the mechanicus. I don't think that they change the template of a cruiser in such a short timeframe. Even if we asume that the changes took place directly after circe 250 years is very short by imperial standards. ^^
c) Imperial Command isn't very open minded, so to say. I think that “more of it†is a far more logical choice than “better equipmentâ€. So if the turret defences were inferior it makes perfect sense that they just raised the numbers. “better eqipment†would be the tau solution to a specific problem, the Imperium usually prefers numbers over quality.
Gamewise
+1turrets works fine against any form of ordnance. I see the problem at another “frontlineâ€: torpedos. You own as well as the enemys.
a) Your own. Without own AC the enemy just sends some Fighters on CAP and your Torps are useless. The logical choice is something what most players woill not like: you use more Ncs. This not only allows you to do some damage, it also has the advantage that you don't neen “reload ordnance†any more, so you are free to use other special orders instead.
b) enemy torpedos. As long as the enemy is in the front arc it'snot a big deal, the 6+ armour helps a lot. But if he somehow gets into your flank you have a problem. I know, this isn't unusual: its always a problem when someone gets into the flank of the “imperial phalanxâ€, but without AC the problem is bigger. Much bigger.
Possible Solutions:
Obvioulsy you need
some AC. I tried out a game completely without AC, it just didn't work. As it would be boring to use two or even tree Mars in every game you should allow other carriers:
- the Jovian should be in
- you should allow the Dictator either as a 0-1 (or 1 per 1500 points) choice or you move him in the battlecruiser section. You can explain this by the fact that the Dictator is a rare ship in Bakka lists.
- another battlecruiser–carrier would be a nice thing. I'm tninking about a “Dictator battlecruiserâ€: a dictator with 45cm Batteries, and a s2@45cm lance for ~ 250 Points.
A more “exotic†idea is another NC variant: the HA wanted that the NC in this list isn't used as a piece of artillery. Instead it should be used in a more aggressive manner. How about this:
“Supernova†assault system
A Novacannon with 10-30cm Range. When you fire, roll the scatter dice and 2D6. One dice is the damage, the other is the scatter distance. The player can freely decide which dice is used for damage and which one scatter. In addition this NC variant can be fired while the ship is under special rules like BFI, AAF or CTNH.
This upgrade is for free, but 50% (rounded down) of the fleets NC's must be exchanged with this variant.
→ the idea is to avoid “long range NC Spam†on the one hand, and on the other hand give the Bakka fleet a potent short range weapon system on the other hand, what IMO fits better to a Big Gun/close combat fleet.
Thoughts?