Hearts of Iron IV: Imperial Japanese Navy -Combined Fleet- at time of Pearl Harbor Attack in December 1941
There are several sources of information regarding the ships that composed the Imperial Japanese Navy (Nihon Kaigun) at different time period. However, it is more complicated to find information regarding the specific order of battles, which includes the divisions and hierarchical command structure of the fleet.
The following Order of Battle will be useful for players of HOI4 to have a historical guideline of the composition and units they should have built by December 1941. It is applicable independently if you starts the game in 1936 or 1939. More importantly, if you want to have more immersion in the game, you could also replicate the structure of the OoB so that not only the ships but also the divisions and squadrons have the same historical names.
The information is directly translated form Japanese written sources, and the translation has tried to conserve the original meaning as much as possible.
Commander-in-chief Admiral Isoroku Yamamoto
[Chokuzoku] Main body Under direct control of the Admiral of the Combined Fleet -Imperial Japanese Navy- Isoroku Yamamoto
1st Battleship Division: Nagato, Mutsu.
24th Special Cruiser Division: Houkoku-maru (Flagship), Aikoku-maru, Kiyosumi-maru.
11th Air Fleet Seaplane-based Carrier: Mizuho, Chitose.
10th Submarine Division: Light Cruiser Kinu (Flagship).
-18th Submarine Squadron: Submarines I-53, I-54, I-55.
-19th Submarine Squadron: Submarines I-56, I-57, I-58.
-21st Submarine Squadron: Submarines Ro-33, Ro-34.
5th Submarine Division: Light Cruiser Yura (Flagship).
-28th Submarine Squadron: Submarines I-59, I-60.
-29th Submarine Squadron: Submarines I-29, I-62, I-64.
-30th Submarine Squadron: Submarines I-30, I-65, I-66.
1st Fleet (Admiral Shiro Takasu)
2nd Battleship Division: Hyuga, Ise, Fuso, Yamashiro.
3rd Battleship Division: Hiei (Flagship), Kongo, Haruna, Kirishima.
6th Heavy Cruiser Division: Aoba (Flagship), Kinugasa, Kako, Furutaka
9th Heavy Light Division: Kitagami (Flagship), Ooi
1st Torpedo Fleet: Light Cruiser Abukuma (Flagship)
-6th Destroyer Division: Rai, Den, Hibiki, Akatsuki
-17th Destroyer Division: Tanikaze, Urakaze, Hamakaze, Isokaze
-21st Destroyer Division: Hatsuharu, Nenohi, Hatsushimo, Wakaba
-27th Destroyer Divison: Ariake, Yuugure, Shigure, Shiratsui
3rd Torpedo Fleet: Light Cruiser Sennai (Flagship)
-11st Destroyer Division: Fubuki, Hatsuyuki, Shirayuki
-12nd Destroyer Division: Shirakumo, Murakumo, Shinonome
-19th Destroyer Division: Izonami, Uranami, Shikinami, Ayanami.
-20th Destroyer Division: Amagiri, Asagiri, Yugiri, Sagiri
3rd Carrier Division: Light Carrier Hosho (Flagship), Zuiho . Escort Destroyer Flotilla: Mikazuki, Yuukaze
2nd Fleet (Admiral Nokutake Kondo)
4th Heavy Cruiser Division: Atago, Takao, Maya, Chokai.
5th Heavy Cruiser Division: Myoko (Flagship), Nachi, Haguro
7th Heavy Cruiser Division: Kumano (Flagship), Mogami, Mikuma, Suzuya
8th Heavy Cruiser Division: Tone (Flagship), Chikuma
2nd Torpedo Fleet: Light Cruiser Jintsu (Flagship)
-8th Destroyer Division: Arashio, Michishio, Asashio, Ooshio
-15th Destroyer Division: Kuroshio, Oyashio, Hayaship, Natsushio
-16th Destroyer Division: Hatsukaze, Yukikaze, Tokitsukaze, Amatsukaze
-18th Destroyer Division: Kazumi, Oboro, Kagero, Shiranui
4th Torpedo Fleet: Light Cruiser (keijyunyoukan) Naka (Flagship)
-2nd Destroyer Division: Murasame, Samidare, Harusame, Yuudachi
-4th Destroyer Division: Nowake, Arashi, Hagikaze, Maikaze
-9th Destroyer Division: Asagumo, Minegumo, Natsugumo, Yamagumo
-24th Destroyer Division: Umikaze, Yamakaze, Kawakaze, Suzukaze
3rd Fleet (Admiral Nokutake Kondo)
16th Heavy Cruiser Division: Heavy Cruiser Ashigara, Light Cruiser Nagara, Kuma.
17th Special Division: Submarine/Minelayer tender (Fusetsu-kan) cruiser Itsukushima, Yaeyama, Special Submarine-tender ship Tatsumiyamaru
5th Torpedo Fleet: Light Cruiser (keijyunyoukan) Natori
-5th Destroyer Division: Harukaze, Katakaze, Asakaze, Matsukaze
-22nd Destroyer Division: Fumizuki, Satsuki, Nagatsuki, Minatsuki
6th Submarine Division: Seaplane-carrier submarine Chougei
-9th Submarine Squadron: Submarines I-123, I-124
-13th Submarine Squadron: Submarines I-121, I-122
12th Air Fleet Seaplane-based Carrier: Kamigawa-maru, Sanyo-maru.
4th Fleet (Admiral Shigeoshi Inoue)
18th Light Cruiser Division: light Cruiser Tenryu (Flaship), Tatsuta.
19th Special Cruiser Division: Submarine/minelayer tender (Fusetsu-kan) cruiser Okishima (Flagship), Protection cruiser (kaibou-kan) Tokiwa, Tsugaru, Tenyoumaru
6th Torpedo Fleet: Light Cruiser (keijyunyoukan) Yubari
-26th Destroyer Division: Oikaze, Hayate, Asanagi, Yunagi
-30th Destroyer Division: Mutsu, Yayoi, Mochizuki, Kisaragi
7th Submarine Division: submarine-tender cruiser Jingei (Flagship)
-26th Submarine Squadron: Submarines Ro-60, Ro-61, Ro-62
-29th Submarine Squadron: Submarines Ro-65, Ro-66, Ro-67
-33rd Submarine Squadron: Submarines Ro-63, Ro-64, Ro-68
5th Fleet (Admiral Boshiro Hosogaya)
21st Light Cruiser Division: Light Cruisers Tama, Kiso and Seaplane-based Carrier Kimikaga-maru.
22nd Special Cruiser Division: Special Cruiser Kuritamaru (Flagship), Asakamaru
6th Fleet (Admiral Mitsumi Shimizu)
1st Submarine Division: submarine-tender cruiser Yasukuni-maru, Submarine I-9 (Flagship)
-1st Submarine Squadron: Submarines I-15, I-16, I-17
-2nd Submarine Squadron: Submarines I-18, I-19, I-20
-3rd Submarine Squadron: Submarines I-21, I-22, I-23
-4th Submarine Squadron: Submarines I-24, I-25, I-26
2nd Submarine Division: submarine-tender cruiser Santosu-maru, Submarine I-7 (Flagship), I-10
-7th Submarine Squadron: Submarines I-1,I-2,I-3
-8th Submarine Squadron: Submarines I-4,I-5,I-6
3rd Submarine Division: submarine-tender cruiser Taigei, Submarine I-8 (Flagship)
-11th Submarine Squadron: Submarines I-74, I-75
-12th Submarine Squadron: Submarines I-68, I-69, I-70
-20th Submarine Squadron: Submarines I-71, I-72, I-73
1st Air Fleet (Admiral Chuichi Nagumo)
1st Carrier Division: Akagi, Kaga
-7th Destroyer Escort Division: Akebono, Usio, Sazanami
2nd Carrier Division: Hiryu (Flagship), Soryu
-23rd Destroyer Escort Division: Kikuzuki, Yuuzuki, Uzuki
4th Carrier Division: Ryujou (Flagship), Kasuga-maru (Taiho)
-3rd Destroyer Escort Division: Shiokaze, Hokaze
5th Carrier Division: Zuikaku (Flagship), Shokaku
Destroyer Escorts: Oboro, Akigumo