Board Thread:Fleet's Prepared-ness/@comment-26811416-20151109180626/@comment-26848183-20151111194847

Strictly talking about events, the 41cm cannons are mainly upgraded for Fusou-class or heavier ships.

Whether it's worth equipping 41cm over the 35cm on your Kongous depends on the difficulty of the map, and the level of your ships; it's all about exchanging firepower for accuracy. In easier maps, you might still hit the 97% accuracy cap even with overweight guns. However, combined fleet already debuffs your ships with a large accuracy penalty, so the accuracy penalty becomes much more noticeable.

http://irasuto-voice.com/archives/2397 estimates Kongo's accuracy penalty looks like this:

41cm x1: 2% penalty

46cm x1: 4% penalty

46cm x2: 8% penalty

It's good practice to have a variety of guns. I sneak 41cm cannons onto my Kongou while sortieing easier maps, since I know she will still hit accuracy cap. But, I'll stick with improved 35cm, 38cm, and 38cm kai on Kongous for combined fleet maps.

I recommend following the guide below, and prioritize improving the 35cm cannons. At least enough for two Kongou-class ships to reach the daytime softcap with parallel engagement. The amount of stars needed to reach softcap listed in this guide. More improved 41cm cannons is nice, but it looks like you only have a handfull, so you might have to push that project aside for later.

http://kancolle.wikia.com/wiki/User_blog:Hayashi_H/Advanced_Equipment_Guide