Combat/Overweight Penalty and Fit Gun Bonus

The "hidden fit bonus" mechanic refers to some ships receiving bonuses or penalties when equipping certain equipment, depending on if the equipment "fits" the class or not.

• This almost exclusively refers to main guns, where each class of ship is engineered to carry up to certain gun calibers, and so, equipping gun turrets of the right caliber or lower will imply an accuracy bonus, whereas using larger calibers will result in some overweight penalties.
• Not to be confused with visible Equipment Bonuses.

As hidden bonuses are unaffected by morale or fleet types (e.g. combined fleets), it can be interesting to utilize those fit bonuses as much as possible.

Such fit mechanics do not apply to abyssals.

Large Caliber Main Guns

Battleships receive 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.

Ship Class	(P)35.6cm(DC), 38cm(K), 30.5cm(K), 38.1cm (/N)	38cmQ, 38cmQK	381mm, 381mmK	41cm			16inch (United States Navy)			16inch (Royal Navy)			46cm			P51cm, 51cm
				41cm, Proto, Kai	3K2	2K2	Mk.7	Mk.7 +GFCS	Mk.6 mod.2	Mk.I	+AFCT	Kai +FCR	Proto	46cm	Kai
Gangut	+7 30.5cm: +10	0	+1	-7			-3			-9~10?	??	??	-7	-18	??	N/A
Kongou-class	+7	0	-2	-5	-5?		-5	-6~7?		-5	-6	-3	-7	-10	-10?
Bismarck Vittorio Veneto-class	+4	0?	+1	-5			-5	-4?		-5	??	??	-7	-10	??
Iowa	+4?	0?	-2?	-5			0	+2					-7	-10	??
South Dakota									-5 M: +4.6
Richelieu	+4	+4~5	-2	-5			-5			-7	-14?	-8	-7	-10	??
Warspite	+6 38.1cm: +8		+1~2	+2				-2?		+5	??	+3~4	-8	-11	??
Nelson	0		0	+3?				0		0
Ise-class Kai/Fusou-class Kai/Ni	+4	0	+2	+2			0			0?			-3	-7 F+: -11?	-4?
Ise-class Kai Ni	+4?	0?		+4?	+4?	+6						+2	??	-7 F+: -11?	??
Ise/Fusou-classes Base	+2	0?	+2	+2			+2	+2?		+3			-3	-7	??
Nagato-class																0
Nagato-class Kai Ni	+2?	0?	+2?	+5	+5	+5~6	0				+4		-2?	-4?	-6?	Nagato: -5 Mutsu: -8
Yamato-class	0												+3	+3	+7	0
Note: Fit gun mechanics are still being investigated to this day, hence the values are not final and may be subject to changes. Values with a question mark either mean that it is not conclusive yet or the conclusion drawn here is not the same as the one drawn by Yumeji. The table shows an estimated accuracy fit bonus based on having one fit gun equipped. For married ships, the overweight penalty is reduced by 40% (A married Kongou with a 46cm receives a penalty of -6 instead of -10, for example). If more than one gun of the same class is used, multiply the modifier by the square root of number of guns. (A Kongou-class with two A class guns equipped for example, that's √2 x 7 = 9.89) If guns from different classes are used together, add the modifiers together. (A Kongou with a 35.6cm and 41cm mixed for example, that's 7 - 5 = 2. Exceptions arise where different guns of the same class give different bonuses on certain ships, notably Gangut. What would happen if you combine 30.5cm and 35.6cm is still under investigation. The information in this table is sourced from this spreadsheet maintained by Dewy with the relevant sources linked in the spreadsheet.
Last Updated: Aug 24th 2020												Made by: Tsubakura

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

[math]\displaystyle{ W = \sum^{\text{All Classes}} \left ( C_{k} M_{k} \sqrt{N_{k}} \right ) \% }[/math]

Where:

• [math]\displaystyle{ W }[/math] is the resulting fit bonus or overweight penalty
• [math]\displaystyle{ C_{k} }[/math] 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.
• [math]\displaystyle{ M_{k} }[/math] 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.
• [math]\displaystyle{ N_{k} }[/math] is the number of equipped guns for that gun class.

Native Guns

Since gun overweight penalty and fit bonuses are not yet all measured for some guns and ships, here is a list of the guns natively used/planed to be used in real life by each ship class.

• The "Twin/Triple" mount distinction is made for convenience, triple guns being heavier than their twin counterpart.
• Equipping ships with those guns may not always be optimal, but this should avoid most overweight penalties.

Large Guns
Nation	Class	Caliber	Twin	Triple
Japanese	Kongou-class Fusou-class Ise-class	35.6 cm	35.6cm Twin Gun Mount 35.6cm Twin Gun Mount (Dazzle Camouflage) 35.6cm Twin Gun Mount Kai 35.6cm Twin Gun Mount Kai Ni	Prototype 35.6cm Triple Gun Mount 35.6cm Triple Gun Mount Kai (Dazzle Camouflage)
	Fusou-class Kai Ni Ise-class Kai Ni Nagato-class	41 cm	41cm Twin Gun Mount 41cm Twin Gun Mount Kai Ni	Prototype 41cm Triple Gun Mount 41cm Triple Gun Mount Kai 41cm Triple Gun Mount Kai Ni
	Yamato-class	46 cm	Prototype 46cm Twin Gun Mount	46cm Triple Gun Mount 46cm Triple Gun Mount Kai
	Yamato-class Kai Ni	51 cm	Prototype 51cm Twin Gun Mount 51cm Twin Gun Mount	Prototype 51cm Triple Gun Mount
US	Colorado-class	40,64 cm	16inch Mk.I Twin Gun Mount 16inch Mk.V Twin Gun Mount 16inch Mk.VIII Twin Gun Mount Kai
	North Carolina-class South Dakota-class			16inch Triple Gun Mount Mk.6 16inch Triple Gun Mount Mk.6 + GFCS 16inch Triple Gun Mount Mk.6 mod.2
	Iowa-class			16inch Triple Gun Mount Mk.7 16inch Triple Gun Mount Mk.7 + GFCS
British	Queen Elizabeth-class	38.1 cm	38.1cm Mk.I Twin Gun Mount 38.1cm Mk.I/N Twin Gun Mount Kai
	Nelson-class	40,64 cm		16inch Mk.I Triple Gun Mount 16inch Mk.I Triple Gun Mount + AFCT Kai 16inch Mk.I Triple Gun Mount Kai + FCR Type 284
Italian	Conte di Cavour-class	30.5 cm	305mm/46 Twin Gun Mount	305mm/46 Triple Gun Mount
		32 cm	320mm/44 Twin Gun Mount	320mm/44 Triple Gun Mount
	Vittorio Veneto-class	38.1 cm		381mm/50 Triple Gun Mount 381mm/50 Triple Gun Mount Kai
German	Bismarck-class	38 cm	38cm Twin Gun Mount 38cm Twin Gun Mount Kai
French	Richelieu-class	38 cm	38cm Quadruple Gun Mount 38cm Quadruple Gun Mount Kai 38cm Quadruple Gun Mount Kai Deux '"Double Twin Guns" in a Quadruple Mount.
Russian	Gangut-class	30.5 cm		30.5cm Triple Gun Mount 30.5cm Triple Gun Mount Kai

Medium Caliber Main Guns

This section is outdated and needs updating. Devs have tweeted about adjusting invisible fits[citation needed], some data is outdated or missing sources. Potential misinformation.

Cruisers can receive accuracy and/or firepower bonuses from using fit guns in their load-out.

Ship Class	14cm Single 15.2cm Single ()	14cm Twin  14cm Twin Kai	15.2cm 15.2cmK	Bofors 15.2cm	15.5cm  15.5cmK	20.3cm  20.3cm(2) 20.3cm(3)		203mm/53	8inch Mk.9  8inch Mk.9 m.2
						Day	Night
CL(T)	+4N +1	??	+2? +2	+3 ??	-2 -2N	-3N?		-2 -2.5N?	-10N?
Agano-class		??	+5 +2N? +2		-2 -2N
Ooyodo		??	+2? +2		+2
CA(V)						0	+5 +5N?		0
Mogami-class					+2
Mogami-class Kai Ni					+5
Zara-class								+1 +1
Seaplane Tenders (AV)		-6N	-6N			-8 -10N			-8 -10N?
Note: Fit gun mechanics are still being investigated to this day, hence the values are not final and may be subject to changes. Values with a question mark mean that it is potentially outdated and might no longer be correct. The table shows an estimated accuracy and/or firepower fit bonus based on having one fit gun equipped. The variable N refers to the number of guns of that category equipped. (Ex: 2 guns of 2N = 4 ACC) Bonuses from guns of different classes are simply added together. The night fit bonus from the 20.3cm series used to be capped at +15%. However, it is unknown whether this cap has been removed or not from the recent updates. There is a possibility that certain fit categories only work during the day. The possibility is plausible, but there's no concrete data proving. The alternative theory is that the night bonus from the 20.3cm series overrides any other categories. The information in this table is sourced from these two spreadsheets (1) (2) the latter maintained by Dewy, both with the relevant sources linked in the spreadsheet. As of 13th December 2018 the hidden firepower bonus of 14cm Twin Gun Mount Kai does not work/does not exist[citation needed].
Last Updated: June 23rd 2019								Made by: Tsubakura

Small Caliber Main Guns

As of 2017/06/23, Yura and Mutsuki/Kamikaze-class destroyers gain bonuses with some main HA guns .

Ship	12.7 cm Single HA Mount (LM)	12.7 cm Twin HA Mount (LM)
Light Cruisers (CL)	+4N	+2 +2N
Yura Kai Ni	+4 +10N
Mutsuki-class	+5
Kamikaze-class	??
Unknown factors: Only Yura K2 and Satsuki K2 were tested[citation needed]. It's unknown whether the other ships in the same class would receive the same bonus or whether it only works for specific remodels. The variable N refers to the number of guns of that category equipped (ex: 2 guns of 2N = 4 ACC). It is unknown whether the 12.7 cm Single HA Mount gives a fit bonus or not. The information in this table is sourced from this spreadsheet maintained by Dewy, but has no sources linked in the spreadsheet.
Last Updated: December 5th 2018		Made by: Tsubakura

DD Fit Accuracy

Certain DDs have a higher-than-expected hit rate when equipped with certain guns or sonars.

• The bonus accuracy likely takes the form: [math]\displaystyle{ \text{ACCURACY}_\text{bonus} = \text{C} \times \sqrt{\text{N}} }[/math]
  • N being the amount of equipment.

Known "C" values
Ship/Class	Gear	C
Tashkent/Verniy	130mm B-13 Twin Gun Mount	5
Fletcher-class	5" Single Gun Mount Mk.30 variants	4
John C. Butler-class	5" Single Gun Mount Mk.30 variants	4
J-class	QF 4.7inch Gun Mk.XII Kai	3
	ASDICs	3
Mutsuki-class	12cm Single Gun Mount Kai 2	5
Source: [1][2]

See Also

Fit gun bonus - Reddit intermediate players' guide