Combat/Overweight Penalty and Fit Gun Bonus

See also: Fit gun bonus - Reddit intermediate players' guide

Fit Bonus and Overweight Penalty
With the introduction of fit gun mechanics on July 28th 2014, ships now will receive fit bonus/penalties depending if the equipped gun fits for the class or if the gun is too heavy for the ship to use.

As fit bonuses are unaffected by morale or combined fleets, it becomes important that you utilize the fit bonuses as much as possible.

Fit mechanics does not apply to the abyssal fleet.

Battleships
Battleships receives accuracy bonuses if the guns are fit and accuracy penalties if its overweight. How much bonus/penalty a ship receives, depends on the battleship class, the caliber and type of the gun and whether the battle takes place during day or night.

Note: The gun classification is only there as a reference for editors and does not reflect the terminologies used in-game.

More generally, the accuracy offset can be defined with the formula:

$$W = \sum^{\text{All Classes}} \left ( C_{k} M_{k} \sqrt{N_{k}} \right ) \%$$

Where:
 * $$W$$ is the resulting fit bonus or overweight penalty
 * $$C_{k}$$ is the main coefficient of the equipped gun class. Refer to the above table for the coefficients applied to each Battleship for their respective guns.
 * $$M_{k}$$ is the marriage coefficient for the particular gun class. Assumes a value of 0.6 if the ship is married, and if the main coefficient is negative.
 * $$N_{k}$$ is the number of equipped guns for that gun class.

Heavy Cruisers
Heavy/Aviation cruisers only require one fit gun to get their fit bonus, there are no overweight mechanics regarding cruisers. Keep in mind that the fit bonus only applies during a night battle and equipping more than one of the same fit gun will not give you any duplicate bonuses. The fit bonuses also apply to torpedo attacks, as there are no distinction between shelling or torpedo based night attacks.

The following guns will give you a fit bonus:
 * +10%
 * +15%

Note: It is currently unknown what would happen if you combine different fit guns.

The following guns are confirmed not to give any fit bonuses:

Light Cruisers
Light Cruisers, Torpedo Cruisers and Training Cruisers all enjoy an accuracy and firepower bonus when equipped with fit guns. Like Heavy Cruisers, Light Cruisers do not have overweight mechanics.

Firepower
Light Cruisers, Training Cruisers, and Torpedo Cruisers enjoy firepower increase when using any of the following gun:
 * 14cm Single Gun Mount
 * 14cm Twin Gun Mount
 * 15.2cm Single Gun Mount
 * 15.2cm Twin Gun Mount
 * 15.2cm Twin Gun Mount Kai

It have been suggested that the increase in firepower might follow this relationship:
 * Increase in Firepower = √(No. of Fit Single Gun Mount) + 2 × √(No. of Fit Twin Gun Mount)

Accuracy
So far, only limited amount of tests have been conducted to study light cruiser fit gun's effect on accuracy so all information in this section are in-comprehensive and they might be superseded by other, more up-to-date investigations when those information are available.

The accuracy fit bonus only applies if 2 or more fit guns are equipped at the same time. Equipping more than 2 fit guns does not increase the fit bonus. Accuracy increase have been observed for the following guns when they are being equipped on CL
 * 14cm Single Gun Mount
 * 14cm Twin Gun Mount
 * 15.2cm Single Gun Mount
 * 15.2cm Twin Gun Mount
 * 15.2cm Twin Gun Mount Kai

Accuracy increase have been observed for the following guns when they are being equipped on CLT Accuracy increase have been observed for the following guns when they are being equipped on CT Other combinations have not been fully tested yet.
 * 14cm Twin Gun Mount
 * 14cm Twin Gun Mount

The possibility of accuracy bonus vary across different ship classes have not been ruled out yet.

Third party Inspection on BB Fit Gun

 * 【艦これ】戦艦主砲の装備補正検証　その4　-フィット・過重量砲の概念は扇?　16inchMk.7など同種主砲2本積み9～11種類戦艦型別命中率分析- (Japanese)
 * 戦艦主砲の装備補正命中率検証 (Japanese)
 * 金剛型 Yumeji396 data (Japanese)
 * 低速戦艦 Yumeji396 data (Japanese)
 * 伊勢改LV99命中検証 (Japanese)
 * Iowa改フィット@2本積み (Japanese)
 * Warspite改フィット (Japanese)
 * ケッコン艦のフィット補正検証まとめ (Japanese)
 * 命中検証 -検証共同- (Japanese)
 * GFCSを加えてまとめグラフ (Japanese)
 * 16inch Mk7+GFCS Tests (Japanese)

Third part Inspection on CA(V) Fit Gun

 * CA SKC,20.3cm(2) and 20.3cm(3) comparison. (Japanese)

Third party Inspection on CL Fit Gun

 * http://kancollexxxxx.blog.shinobi.jp/Entry/4/ (Japanese)
 * https://docs.google.com/spreadsheets/d/1Vj_DAMxkZk2ZFZy8mYn6_YM_g1TDW4G7Ax4bBZa_yM8/edit#gid=0 (Japanese)
 * https://docs.google.com/spreadsheets/d/17FrSqk0-yo2KnGux0YDLzeznUeYS8Wu5ojQ8bjsTbL8/edit#gid=449414457 (Japanese)