Type 4 Passive Sonar

[Edit] Type 4 Passive Sonar No.149 四式水中聴音機
Small Sonar Effects: +1 +12 +1 Scrap value: 1 3 (Unbuildable)
Refittable Ship Types
Coastal Defense Ship	Destroyer
Light Cruiser	Torpedo Cruiser
Heavy Cruiser	Training Cruiser
Aviation Cruiser	Fast Battleship
Battleship	Aviation Battleship
Light Carrier	Standard Aircraft Carrier
Armored Carrier	Seaplane Tender
Submarine	Aircraft Carrying Submarine
Submarine Tender	Fleet Oiler
Repair Ship	Amphibious Assault Ship

Introduction

小型艦艇にも装備可能な、新型パッシブソナー兵装です。
九三式水中聴音機に比べて、その対潜発見能力は格段に向上しました。
数は少ないですが、大戦末期に建造された後期型の駆逐艦などの対潜兵装として装備されました。

This SONAR can be equipped on smaller ships, and is a new type of armament: the "passive SONAR."
Compared to the type 93 SONARs, this has increased ASW.
There are few of these because it was made in the later part of the war, and were equipped by some of the newer destroyers.

Notes

ASW Damage Synergy
Small Small Sonars	Type 93 Passive Sonar Type 4 Passive Sonar Type 3 Active Sonar Type 3 Active Sonar Kai Type124 ASDIC Type144/147 ASDIC HF/DF + Type144/147 ASDIC
Large Large Sonars	Type 0 Passive Sonar
DCP Depth Charge Projectors (DCP)	Type 94 Depth Charge Projector Type 3 Depth Charge Projector Type 3 Depth Charge Projector (Concentrated Deployment) Prototype 15cm 9-tube ASW Rocket Launcher RUR-4A Weapon Alpha Kai AP Mk.32 ASW Torpedo (Mk.2 Thrower) AP
DCR Depth Charge (Racks) (DCR)	Type 95 Depth Charge AP Type 2 Depth Charge AP Lightweight ASW Torpedo (Initial Test Model) AP Hedgehog (Initial Model) AP Type 2 Depth Charge Kai Ni AP
Other ASW Mortars	Type 2 12cm Mortar Kai Type 2 12cm Mortar Kai (Concentrated Deployment)
ASW Damage Modifiers: [math]\displaystyle{ \text{Mod}_\text{synergy} = {Mod}_\text{1} \times {Mod}_\text{2} }[/math]
[math]\displaystyle{ {Mod}_\text{1} }[/math]	+ (Any Sonar + Any Depth Charge)	1.15
[math]\displaystyle{ {Mod}_\text{2} }[/math]	DCP + DCR and NO Small	1.1
	Small + DCP + DCR	1.25
Examples
[math]\displaystyle{ \text{Mod}_\text{synergy} }[/math]	Small + DCP + DCR	1.4375[math]\displaystyle{ 1.15 \times 1.25 }[/math]
	Large + DCP + DCR	1.265[math]\displaystyle{ 1.15 \times 1.1 }[/math]
Armor Penetration
Indepentant of synergies, some equipment provides additional armor penetration to ASW attacks. The affected equipment are: DCR: Type 95 DC, Type 2 DC, Lightweight ASW Torpedo, Hedgehog, Type 2 DC K2 DCP: RUR-4A Weapon Alpha Kai, Mk.32 ASW Torpedo (Mk.2 Thrower). The flat armor penetration value is calculated as follows: [math]\displaystyle{ \text{Pen} = \sum\limits_{\text{Equipment}} \Big( \sqrt{\text{ASW}_\text{Equipment} - 2} + \text{Mod}_\text{ship} \Big) }[/math] With [math]\displaystyle{ \text{ASW}_\text{Equipment} }[/math] the base ASW stat of the applicable equipment, Visible Bonuses and Improvements are not counted here. [math]\displaystyle{ \text{Mod}_\text{ship} }[/math] being 1 for DE, 0 otherwise, Note Armor penetration from equipment stacks, The final armor of the targetted submarine cannot go below 1.

How To Obtain

Upgradeable from: Type 93 Passive Sonar

From quest: B74

From limited-time quest: SB05

Ranking reward for:

• Aug 2015: 1-5 (x2), 6-20 (x2), 21-100 (x2), 101-500
• Apr 2016: 1-5, 6-20, 21-100, 101-500
• Dec 2016: 1-5, 6-20, 21-100, 101-500

Event reward for:

• Fall 2015 Event E-3: Hard

Uses

Used to improve: Type 4 Passive Sonar

Updates History

• 2015-09-22: Implemented as ranking reward
• 2015-09-25: Became improvable
• 2017-09-29: Stats increased: +0 → +1
• 2020-01-14: Visible bonuses added
• 2021-03-01: Visible bonuses added for Katori-class
  

Fit Bonuses

Ship	Extra Requirement									Note
Yuubari Kai Ni D					+3				+5	Non-stackable
Noshiro Kai Ni					+2				+4	Non-stackable
Isuzu Kai Ni Naka Kai Ni Yura Kai Ni Yuubari Kai Ni/Toku Yukikaze Kai Ni					+1				+3	Non-stackable
Akizuki-class					+1				+2	Non-stackable
Katori-class					+2				+3	One-time between Type 93 Passive Sonar, Type 3 Active Sonar, Type 4 Passive Sonar and Type 3 Active Sonar Kai

Akashi's Improvement Arsenal

Type	Name	★	Resource							Day							2nd Ship	Note
										Sun	Mon	Tue	Wed	Thu	Fri	Sat
	Type 4 Passive Sonar	0	10	0	50	60	5/7	3/5	2x	A	Y K	K	T	I Y	I	I	Isuzu Kai Ni Yuubari Kai Ni Katori Kai Akizuki Teruzuki
		6					6/10	4/6	1x
		10					-	-	-