During events, qualified players gain access to special a time-limited world with special maps, which usually reference historical operations; the only exception was a collaboration event with the Arpeggio franchise: Aoki Hagane no Arpeggio: Ars Nova. Event maps stay up for an indeterminate amount of time, usually measured in weeks, which grew as the game progressed to be anywhere between 2 and 8 weeks.

Event maps pose considerably higher challenge levels compared to normal maps, employing exclusive special Abyssal Fleet bosses and mechanics, such as the Combined Fleet.

Current Event

Spring 2022 Event - Fierce Battle! R-Area Operation

Past Event List

The past events are listed below for reference.

Spring 2013 Event - Break into the Enemy Anchorage!

Summer 2013 Event - Southern Waters Assault Reconnaissance!

Fall 2013 Event - Final Battle! Iron Bottom Straits!

Christmas 2013 Event - Intercept! Fleet of Fog

Spring 2014 Event - Recon planes, launching!

Summer 2014 Event - Operation AL/MI

Fall 2014 Event - Operation Kon

Winter 2015 Event - Counter-attack! Assault on Truk Anchorage

Spring 2015 Event - Order! Operation 11

Summer 2015 Event - Counterattack! The Second Operation SN

Fall 2015 Event - Breakthrough! Maritime Transport Operation

Winter 2016 Event - Sortie! Operation Rei-Go!

Spring 2016 Event - Deployment! Land-based Aerial Division!

Summer 2016 Event - Counterattack! The Second Battle off Malay Peninsula

Fall 2016 Event - Announcement! The Third Fleet Operation Act

Winter 2017 Event - Reconnaissance Force Emergency Deployment! Operation "Hikari"

Spring 2017 Event - Sortie! Fifth Fleet To the North East!

Summer 2017 Event - Crossing into the West Again! The European Rescue Operation!

Fall 2017 Event - Showdown at Operation Shou-gou! Battle of Leyte Gulf (Part 1)

Winter 2018 Event - Showdown at Operation Shou-Gou! Battle of Leyte Gulf (Part 2)

Early Fall 2018 Event - Set Sail! Combined Fleet, to the West

Winter 2019 Event - Interception! Operation Buin Defense

Spring 2019 Event - Commence Allied Relief! "The 2nd Hawaii Operation"

Summer 2019 Event - European Counterattack Operation! Commence "Operation Shingle"

Fall 2019 Event - Advance! The 2nd Southern Operation

Hinamatsuri 2020 Mini-Event - Peach Festival! Offshore Waves

Rainy-Summer 2020 Event - Stop the Invasion! Island Defense Fortification Operation

Fall 2020 Event - Escort! Fleet Transport Operation

Spring 2021 Event - Clash! Night Battle off Lunga

Summer 2021 Event - Reinforcement Transport Operation! Battle of the Mediterranean

Fall 2021 Event - Return of the Naval District Saury Festival

Winter 2022 Event - Annoucement! Operation Sho-Go 3 Alert!

Event Preparation

Full Article: Help:Event Preparation

Stockpiling

Accumulating a stockpile of resources () and consumables (buckets and flamethrowers) prior to the event start or during the weeks that lead up to an event is extremely recommended.

Using the soft cap mechanic to your advantage might be beneficial should the situation demand it. For each resource under the soft cap, it is generated up to 1440 for and 480 for , per day.
- For reference, expedition 5 being run non-stop will bring in a gross of 3850 fuel and ammo, and 257 steel and bauxite per day.
- As buckets and flamethrowers do not regen over time, focusing on stocking them might be preferable on a higher priority. Expeditions 02, 04 & A2 for buckets and 2-1 for flamethrowers are good ways to farm with very high efficiency and low maintenance.
- Fuel and ammo are the most used resources and also the most easily obtained resources through expeditions. Steel is used on a much smaller scale in comparison, but is substantially harder to stockpile in a shorter period of time. Bauxite uses will vary depending on each particular map.

Event Mechanics

Participation requirements

To take part in any event, a player MUST HAVE at least:

A 75% sortie win ratio.
5 empty ship slots.
20 empty equipment slots.

Special Mechanics

In addition to regular Sortie mechanics, events often involve some specific or rarer mechanics :

Map Clearing Medals
Hard	Medium	Easy	Casual

Depending of the HQ level, it is possible to choose between:

Hard ("operation A", 甲), at HQ 80+
Medium ("operation B", 乙), at HQ 35+
Easy ("operation C", 丙), at HQ 1+
Casual ("operation D", 丁), at HQ 1+

The map difficulty will directly affect the enemy encounters, making them more numerous, with higher stats, or even replacing weaker ships with stonger ones. Additionaly, will vary:

The maps' phases' gauges (HP/TP),
The amount of map gimmicks to complete,
The LoS requirements,
The maps' rewards,
The ship Drops.

Changing difficulty is possible but limited:

When switching from any "lower" difficulty to any "higher" difficulty, the map will fully be reset.
When switching from any "higher" difficulty to any "lower" difficulty, the map will stay in the very same state it was previously, with only +25% of TP/HP being reset on the current phase's TP/HP bar.
- Gimmicks might also be reset when applicable, notably the debuffs.

Beginning with the second map, difficulty progression rules apply.

In order to play a map on Hard difficulty, the prior map must have been completed on either Medium or Hard.
In order to play a map on Medium difficulty, the prior map must have been completed on either Easy, Medium, or Hard.

To simulate simultaneity of battles in different locations, Fleet Tags conditions & deployment restrictions are employed.

Ships not already tagged will be tagged with the associated tag of the map phase when deployed. This tag will be applied regardless of the difficulty and can't be removed by any measure before the end of the event.
One map can use multiple tags, usually separated by phases or fleets.
Several maps can share one or more tags.
On Medium or Hard difficulty, ships must have either the same tag as the map/phase they are being deployed to, or have no tag at all.
- This requirement is sometimes waived on certain maps, mostly on the last map of the event where tags only matter on Hard.
- Once the event is cleared (last map of the EO), all tag restrictions stop getting enforced on every map (tag routing will still apply).

The Combined Fleet (CF), a fleet assembling both the 1st and 2nd fleets, may come back.

The CF is only available for the two 1st fleets, where the 2nd fleet can be merged with the 1st one in the "Fleet menu".
The CF cannot be used in anything outside of event sorties.
3 different types of CF are available, depending on the map requirements and the current fleet setup.
CF with a flagship that carries the Fleet Command Facility, will be able to make use of the Evacuation mechanic.
- The evacuation requires an escort destroyer.
- Only one ship can be evacuated per battle.

The Flagship of the Escorting fleet cannot sink!

The Striking Force Fleet (SF), a fleet with seven ships, may come back.

The SF is only available for the 3rd fleet, where an extra 7th ship can be added in the Fleet menu.
The SF cannot be used in anything outside of event sorties.
A SF with a flagship that carries the Striking Force Fleet Command Facility, will be able to make use of the Evacuation mechanic.
- Only one ship can be evacuated per battle.

The Vanguard Formation can be used.

This formation will organize the fleet such that the 2 to 3 last ships protect the 2 to 4 first ships of the Fleet.
This formation is available for single and Strike Force fleets made of 4 to 7 ships.
- The formation makes ships way more evasive in combat, especially DD, and more accurate against DD, especially PT Imps.
- This formation is available only during the duration of the event, on the event's maps as well as on the regular maps.

NPC Friendly Fleets (FF) may be introduced to the event.

FFs act as another unit that appears in particular battles to help aid the fleet when attacking the enemy.
It is possible to choose between using "normal only" or "normal and powerful" FF in the main menu.
- Powerful FFs have an additional cost of 6 Instant Constructions for each time they are deployed in a battle.
  - The blowtorches won't be consumed unless a powerful FF appears.
- If activated, one FF is randomly selected from a preset list of fleets to help the fleet.
- Which ships are in the fleet will influence which FF can help, excluding the FFs containing ships also in the main fleet.
- The FF will appear at the start of either day or night battle, depending on the node.
FFs are usually available sometime after the start of the event, to help Admirals facing difficulties clearing the maps.

Most maps have various bonuses, coming in many shapes. Since most of those bonuses follow the historical formations/tactics used in the relevant operations, they are referred to as "Historical Bonuses". Such bonuses are also found on 7-4 and 7-5.

The bonuses can be given to:
- Ships, including all remodels,
- Ship types, with all ships of a given type sharing a bonus,
  - In those cases, types do not overlap (e.g. a CLT does not count as a CL),
- Ships Nationalities, with foreigners (non-Japanese) sharing a bonus,
- Equipment, with some types or specific ones giving a bonus,
  - It is only applied to the ship they are equipped on,
  - For planes, those bonuses won't work if the plane count is 0, but for the Foreign Plane Bonuses.

Then, bonuses can be applied:
- Map-wide, working on all nodes
- On some Nodes only, with usually boss or gimmick nodes having some bonuses,
  - Those node bonuses are often split following the map's phases.
- Against some abyssals specifically,
  - Usually bosses and their escorts,

Bonuses can stack or not between each other depending on the case.

Bonuses are either damage, accuracy, and/or evasion,
Damage and evasion bonuses are "post-cap",
Some gimmicks like the map's phase can further affect the bonuses (usually the Debuff).

Completion Gimmicks might be required to further progress the map, demanding certain conditions to be accomplished on a given map to unlock several things :
- Boss Debuffs, where once the "Last Dance" of the final boss of a given map is reached, its debuffed form can be unlocked.
- Map phases, where some map areas need to be unlocked, like on 7-2, 7-3, and 7-5.
  - Map areas can either be a path to the next boss, an intermediate path asking for new gimmicks, or a shortcut.
- LBAS Relocation.
- Choosing a higher difficulty on an event map will reset it to its initial state.
- These conditions range from reaching certain nodes, defeating specific nodes, attaining air superiority on certain nodes, and defending against Air Raids. As soon as all the given conditions are met, the map advances to the next phase. Lower difficulties may require fewer conditions to be met to complete the phase. The order in which the gimmicks are completed does not matter.
- Completing a gimmick will play a "bell" sound once back in the main port (Play Bell Completion Sound Effect).
- Nodes required to be visited/defeated in gimmicks are highlighted.

Special Nodes:
- Emergency Anchorage Repairs:
  - Akashi Kai, Asahi Kai, and Akitsushima Kai can be capable of conducting emergency repairs; however, only Akashi has the full capabilities compared to the others.
  - This consumes Emergency Repair Materials.
  - AR Kai, Akitsushima Kai, and AO Kai will also take advantage of the special routing linked to this mechanic, even if it is not used.
- Enemy Ambush Nodes, "off-route ambush nodes",
  
  Ambush
  - They serve as a "radar check", with fleets lacking enough Surface Radars being off-routed there,
  - The fleet will not be able to fight against the enemy fleet.
- Airstrike Supported Battle Nodes, ("ASS nodes") "off-route combat nodes",
  
  ASS
  - The enemy fleet will consist of "normal surface enemies" (4-5 SS so far), followed by "air support enemies" (1-2 CVL so far), bringing air support, and that cannot be attacked,
  - By meeting certain conditions, these nodes can be evaded.
- "Installation Nodes", being most nodes having one or more Installation in it, and were Barrage Balloons can be deployed.
- "Atoll Nodes", being some nodes located on atolls, and were Ka-Tsu tanks
  spacial attack can be triggered.

High-Altitude Abyssal Bombers that are resistant to all types of interceptors other than the Land-Based Rocket Interceptors

.

Superfortress Air-Raid Sequence, a QTE where the LBAS is attacked by bombers, and where the player must click on a button at the right moment to obtain better interception, using "Land-based high-altitude interceptors".

AGDP Arctic Gear & Deck Personnel (AGDP) needs to be equipped on CV(B/L), Ise-class Kai Ni, and Akitsu Maru Kai, to sortie them on "arctic" maps. Exclusive to the Fall 2020 Event and Early Spring 2024 Event so far.

Bug: It is possible to save a sunk ship in events:

When sinking a ship on a "time-limited event map", by closing the game before the battle ends (before battle result screen is shown), and refraining from logging in until a maintenance in which the time-limited map is removed from the game occurs, upon entering the game after the map is removed, the sunken ship will remain in the game, at 0 HP and with the "Sunk" status.
The ship can be repaired as per normal; removing this status, and sortieing it at 0HP will cause it to return to 1HP.
Opening the game at any time before the map is removed, or sinking a ship in a normal map will not enact this behavior, regardless of whether a maintenance has occurred or not.

This probably comes from the fact that the game is unable to resolve the battle state due to the map the ship was sunk in, no longer existing. This presumably aborts the game's attempt to check for and delete the sunken ship in question from the roster.

Some error messages you may encounter before a sortie.

Do note that:
- Most errors are "general" and can be seen in many situations,
- Some errors are event only, being liked to event maps/locks/mechanics.