Originally Posted by Sonlirain
Personally i think there are only 3 good guns for Japan.
1. 3.9" A is a true DP gun that can fire both HE and AA shells. Useful on DDs and the ECL.
2. 4.7" Probably the best DP gun in the game. Not terribly powerful alone but Yamato and SuperYamato are packed with T slots that allow those guns to clear the sky.
3. 6.1" A is an absolute beast that will kill planes with a single shot. As a downside not many ships can use it and those that do are either top tier BBs or CAs fully dedicated to AA.
not everything got mentioned here...
IJN has 2 sets of spam guns:
3" A DP guns, with GA of 48, reload of 0.96s, as you can see low range and low damage
3.9" A DP guns, with GA of 38-39, reload of 1.2s (this set is great for AA spamming).
IJN has 3 long range AA gun sets:
4.7" single A DP gun - the one which gets forgotten always - GA of 25!
4.7" dual A DP guns - GA of 27 and just great guns
6.1" tripple A DP guns - GA of 27, i have killed entire wave of DBs just with one salvo!
DD3 Tsukikei is a great small boat ready for AAing, just load 5x 4.7" duals
Kitakami CL is not bad too, 3.9" duals or 4.7" duals, your choise to spam or to snipe.
Mogami CL, Myoko CA and Mogami CA are best with 6.1" tripples, if you are good, enemy ships will try to sink you first instead of your team's BBs.
PBB B65 is good with 4.7" duals( or 4.7" singles for ultimate range)
Yamato, Musashi, Shinano, Super Yamato are best with combination of 4.7" duals and 6.1" tripples, but due to number of guns, 4.7" singles will do fine snipping too.
Amagi, same as B65, since 6.1" tripples has low ammo on it.
Overall, personally i think IJN AA is the best one in game, versatile - from long range to low range, from weak AA shell damage to very powerfull shells, muzzle speed is great too - don't have to wait long till shells reach their max range (though MN has the best muzzle speeds), IJN also has good ships for AAing.
Happy plane hunting, enjoy free experts ;)