IJN gun armaments

[Nemo121]

I'm looking at IJN AAA upgrades and while it is relatively simple to postulate upgrades for the 4.7 and 5 inch guns to give them longer barrels and DP mounts so as to make reasonable AAA guns the question of mountings comes into play.

From what I've read the 3.9inch guns had some sort of semi-automatic feed. If this is so then would there have been any unsolvable logistical problems blocking the making of either a side by side or quadruple ( 2 up, 2 down ) 3.9 inch mount to act as dedicated AAA armament for larger IJN ships ( I'm thinking BBs and CAs). I think that dual 4.7 or dual 5inch mounts would make great DP mounts for DDs and CLs etc but am really looking for something a little more effective as the AAA armament for CAs and BBs and quadruple 3.9 inch mounts certainly look like they'd do the trick. The question is just how quickly could one fire a quadruple mount setup and could some sort of semi-automatic loading setup have been created for 100mm projectiles?

[bklooste]

Look at the scaled down 80/60 used on the Agano and pos the Ibuki for a dedicated AA weapon which is still usefull against smaller ships in DP roll...Here are the mounts ( detail from navweap) . Obviously this is where Japan were going for AA.
 
               Turret weight     Range Shell*         Training ( deg / s)     Shell           ROF     Barrel life
100/65           34.5t               11Km                  11-16                    13kg         15-21   350-400
80/60             12.3t               9km                    16-18                    6.5kg          25      600
 
Effective ceiling about 80% ( so 80mm is about 23k feet)
 
While the 100/65 could possibly have become a triple mount at ~45-50 tons it would be one heavy turret for AA use , the weight would reduce training also and the Japanese always skimped on these motors. You could instead have  almost 3 triple 80/60 mounts at a more reasonable 16-17.6tons each. These would also aleviate the need to develop a medium 40mm AA system. A 250 Accuracy wouldnt go astray either ... 
 
You could also build a non turreted single gun mount  with a thin gun shield at prob 5 tons ( including the 3 ton gun)with a lower ROF which would make an interesting upgrade for a triple 25mm ( ~2ton)  so instead of fill their ships with 25mm you can provide a more balanced mix.
 
Best of all this was a real historical weapon.