abstract
| - The opening anti-submarine attack (OASW) can be performed by any ship with displayed ASW value of 100 or greater (ship's ASW stat + any equipment ASW stats, not counting equipment improvements) and at least one sonar.
* [[|]] [[File: Battle.jpg|link=|]] is an exception and can always perform OASW, even with less than 100 displayed ASW or without any ASW equipment.
* [[|]] [[File: Battle.jpg|link=|]] can perform OASW with Type 97 Torpedo Bomber (931 Air Group) or Tenzan (931 Air Group) and displayed ASW of 65 or greater. For [[|]] [[File: Battle.jpg|link=|]] and [[|]] [[File: Battle.jpg|link=|]] the bombers are not required, 65 displayed ASW is sufficient (however, if she is not using a torpedo or dive bomber with ASW stat, she will be able to perform OASW attack but will be unable to perform ASW attacks in the shelling phase). OASW attacks will be performed even if she is at medium damage or all her planes were shot down.
* can perform OASW with displayed ASW of 60 or greater. With displayed ASW of 75 or greater and equipment ASW of 4 or greater they can perform OASW without a sonar equipped.
* If several ships fulfill the requirements, then they all can perform preemptive attacks, each attacking a random submarine in the enemy fleet. The firing order is determined by the range order, similar to the First Shelling Phase. The order for ships of the same range is random.
* The damage follows the usual ASW formula and is affected by the usual modifiers (formation, engagement, health, ammo), as well as equipment improvements. The following tables show how much base ASW is needed (in form of required ship level) to enable OASW with a given equipment setup (T4: Type 4 Passive Sonar, T3: Type 3 Active Sonar, DC: Type 3 Depth Charge Projector).
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