Combat/Night Battle

Night Combat

 * The ammo usage on that node is increased by 150% if night battle is entered from day. As most nodes on normal and event maps alike uses 20% ammo, this will be increased to 30% for example.
 * This also means that entering night battle in event submarine nodes doesn't cost anything extra, as those nodes uses 0% ammo.
 * Night battle damage depends on both the Firepower and Torpedo stats for attack power. Consequently, DDs, CLs, CLTs and CAs have drastically increased strength at night.
 * Any vessel at night must not be heavily damaged ( 大破 ) before attacking in order to participate in night battle.
 * Certain combinations of weapon equipment (Main Guns, Secondary Guns, Torpedoes) will cause Cut-In or Double Attacks at night, greatly increasing accuracy and/or firepower
 * Auxiliary equipment (e.g RADAR, SONAR, Depth Charges, Searchlights, Turbines, Special ammunition, Pure AA Equipment, Torpedo Bulges, and Midget-subs) will not affect the combination.
 * If night combat nodes are anticipated, it can be very helpful to utilize specialized night battle equipment such as Star Shells and Searchlight. Type 98 Recon Seaplane (Night Scout) is also an option.
 * All ASW attacks during night battle are reduced to scratch damage. This means that submarines are impossible to kill during night, as you cannot destroy a ship with scratch damage. However, in battles starting at night and/or Combined Fleet sorties, ASW damage will apply as normal.
 * Formation damage modifiers and Engagement Form damage modifiers do not apply in Night Battle (i.e. they are always 100%).
 * The animation for ships equipped with 2 different torpedoes may be different but the damage output is still the same.
 * A Prototype FaT Type 95 Oxygen Torpedo Kai + 61cm Quint (Oxygen) Torpedo Mount will show a cut-in animation of FaT+Quint+Quint and if equipped the other way around, the cut-in animation will show Quint+FaT+FaT. However, both animation produces the same damage output.

Night Battle Special Attacks
Night battle special attacks allow your ship to double attack (DA) and cut-in (CI) at night. Compared to artillery spotting, these special attacks are less demanding on equipment setups and give different bonuses. Note that it is important to realize the differences between the two types of special attack and know when to use which.

Requirements

 * Not in heavily damaged ( 大破 ) state
 * Certain equipment setups (see below)

Setups and Attack Types
Different setups have chances to trigger different modes of attack. Attack modes are ONLY determined by the prerequisites. Also, feel free to add any auxiliary equipment (AP shell, seaplane, AA gun, etc.).on the remaining slots.
 * When your set up fulfills the prerequisite for multiple attack modes, the one closer to the bottom of the list will be considered.
 * Note the night battle damage cap (300) applies after these modifiers.
 * If two simultaneous attacks are made with cutins, the total damage is displayed together but the Damage Cap (and Enemy Armor reduction) is applied separately to each attack.
 * When either DA or CI is not triggered by chance, the ship will just do a normal single attack.

Night Double Attack Chance
Has a very high (~99%) and relatively consistent activation chance (source). Activation rate is not dependent on luck. This typically results in more consistent and higher average damage than cut-in setup for ships with normal luck values.

Night Cut-in chance:
It is currently known that Night Cut-in chance is affected by the type of cut-in attack used, luck, health, flagship position and night battle equipment activation.

Note that there is a soft cap of 50 on cut-in chance.

Note: Keep in mind that proposed formulas are only a theory and is thus not fully confirmed.

Base Formula ≦ 50 :

$$ ({\text{Level} \over {20}} + {\text{Luck} \times {0.85}} + {\text {Cut-In Type} } + {\text {Other Modifiers}} - {\text {Enemy Luck} \over {10} })\% $$

Proposed Formula #1 ≧ 51 (Theory): $$ ({\text{Level} \over {20}} + 42.5 + {\text{Luck} - 50 \over {6}} + {\text {Cut-In Type} } + {\text {Other Modifiers}} - {\text {Enemy Luck} \over {10} })\% $$

Proposed Formula #2 ≧ 51 (Theory): $$ ({\text{Level} \over {20}} + 42.5 + {\text{Luck} - 50 \over {12}}x^2 + {\text {Cut-In Type} } + {\text {Other Modifiers}} - {\text {Enemy Luck} \over {10} })\% $$

Other Modifiers

 * No bonus is received when ships enter light damage state.
 * The bonus received when ships enter moderately damaged state, is ~10%, much lower than it first was proposed.
 * Skilled Lookouts seem to give a luck-type bonus to activation chance, as the cut-in chance bonus is negligible near and above the cap. (source)
 * The exact bonus is still unclear, but the end result seems to be about 3-4% increase in cut-in chance if significantly below the cap.
 * The effect of over the caps is negligible, thus going over it is generally not recommended.
 * Marriage itself does not increase cut-in chances.