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Japanese Order of Battle

We present here the Japanese order of battle from 7 December 1941 on. Units that deployed as part of a higher echelon (such as regiments assigned to divisions) are not listed separately. Also, units redesignated from other units are not included. The intent is to give a reasonable reinforcement schedule for war games.

Tabulated information

Unit. This is the name of the unit.

Commander. This is the commander of the unit at the time of its activation. For units already active when war broke out, it is the commander of the unit on 7 December 1941. In general, we do not display commanders below flag or general rank. Ships showing a commander are the flagship of that commander.

Start. This gives the date and location of the unit's activation. For units already active when war broke out, only the location is given (at 8:00 AM on 7 December 1941, Hawaii time). If no location is given, a unit should be assumed to be at the same location as its operational headquarters (or administrative headquarters if no operational assignment is given.) Naval headquarters are located on the flagship of their commander unless otherwise specified.

Administrative Assignment. The administrative assignments in this table represent the formal organizational structure. The initial order of battle is sorted by administrative assignment, such that every unit appears after the unit to which it is administratively assigned.

Operational Assignment. The operational assignment, if one is given, represents temporary attachment to another unit for a single operation. For example, 16 Division was administratively a part of 14 Army when war broke out, but at that moment it was preparing to embark with (and came under the operational control of) Lamon Bay Force.

Notes. Miscellaneous information about a unit, such as its manpower and equipment, where it was raised, what its initial orders were, what its subunits were, and how well it performed in battle.

Organization of the tables

The order of battle tables are laid out for maximum readability by software tools while retaining some semblance of human readability. Because the complete orders of battle for the major powers are many megabytes in length, we have broken the tables up into individual sections of less than 400K to avoid difficulties with older Web browsers.

In addition to the displayed text and associated links, each unit has an HTML anchor with a unique identifier based on the unit name. For example, the entry for 14 Army includes the anchor 14_Army, which appears immediately before the unit name in the table. These anchors are used to cross-reference the tables but may also be of use to software tools scanning the tables.

We are considering offering the complete orders of battle as SQL files or as C++ code. Users of the Encyclopedia who desire these or other formats may write to trollingshallows@msn.com and make their desires know.

The order of battle

Initial Japanese Army order of battle

Initial Japanese Navy order of battle, 1 Fleet to 4 Fleet

Initial Japanese Navy order of battle, 5 Fleet to 11 Air Fleet and naval districts

Reinforcements, 1941-1942

Reinforcements, 1943

Reinforcements, 1944

Reinforcements, 1945

Replacements

The air and ground replacement schedule is difficult to work out for any power. The replacement model for the influential Pacific War (Victory Games 1985) called for an initial pool of 100 replacement battalions and subsequent accumulation of 10 replacement battalions per month, with the replacement accumulation rate reduced in proportion to the loss of oil fields or destruction of Japanese industry by strategic bombing. These replacements could be applied to any land unit, and there were rules for using cadre and replacements to create new regiments.

The actual data on Japanese military induction are as follows (Drea 2009):

Induction of military manpower (thousands)

Class   
1942
1943
1944
1945
A Examined
A Inducted
190
190
184
184
310
310
155
155
B Examined
B Inducted
401
150
412
176
924
690
477
345
C
84
85
176
90
D
21
21
44
23
E
7
7
14
7

It can be seen that, as the war progressed, fewer of the more desirable recruits were exempted from service or rejected for medical reasons, and more of the less desirable were called up. It can be seen that the numbers in the combat categories (A and B) averaged about 600,000 per year or 50,000 per month, so the figure of ten replacement battalions per month is on the stingy side. On the other hand, even the Japanese Army had a significant division slice, so the numbers may not be entirely unreasonable.

Japan trained about 46,000 pilots during the war. The Pacific War model for air reinforcements and replacements did not distinguish the two, nor did it distinguish services or aircraft type. A single pool of air replacement/reinforcement squadrons was built up, starting in January 1941, at the rates shown in the table below.  A training model was implemented by having these replacement squadrons enter the pool initially untrained. Replacement squadrons with over two years' training were considered fully trained; those with over a year's training were considered moderately well-trained; and those with over three month's training were considered poorly trained. Replacement squadrons with less than three months' training were usable only as kamikazes. Training ceased when a squadron was deployed for combat, but there were mechanisms for improving the training level of deployed squadrons if they performed well in combat. The replacement model also had provisions for improving the experience level of replacement squadrons by sacrificing fully trained squadrons to serve as flight leaders. As with the ground replacement model, there were provisions for reducing the rate at which squadrons entered training if Japan lost control of oil fields or suffered damage to industry. While crude, this model nicely captured the effects of attrition on the pilot skills of Japanese air squadrons, as well as the effects of the submarine blockade on training schedules.

Note that this air replacement/reinforcement schedule assumes that availability of pilots is more crucial than availability of aircraft. This was largely the case during the war.

Air squadron replacement schedule

Months    
Squadrons entering training
1941-1 to 1942-8
4 per month
1942-9 to 1942-12
8 per month
1943-1 to 1943-6
15 per month
1943-7 to 1943-9
20 per month
1943-10 to 1943-12     
25 per month
1944-1 to 1944-6
35 per month
1944-7 to 1944-12
30 per month
1945-1 to 1945-3
20 per month
1945-4 to 1945-7
10 per month

Another clue to air replacements is the Navy fighter pilot class sizes and dates given by Hata et al. (1989). This data is incomplete and somewhat confusing, but we can extract the following lower limits on replacement numbers:

Class
Training start date
Training end date
Total class size
Number of fighter pilots
Ko 5
1939-10
1942-1
41+
41
Hei 3/17
?
1942-3
102+
102
Otsu 10
1938-11
1942-3
35+
35
Yo 8
1941-4
1942-4
43
7
Hei 3/18
?
1942-5
30
30
36
1941-5
1942-6
125
29
Ko 6
1940-4
1942-7
46+
46
Hei 4/21
?
1942-7
56
56
Otsu 11/21
1939-6
1942-7
20+
20
Hei 6
?
1942-9
70+
70
Otsu 11/23
?
1942-9
48+
45
Otsu 12
1939-11
1943-1
63+
63
Yo 9
1942-1
1943-1
34
9
Yo 10
1942-1
1943-1
48
13
37
1941-11
1943-2
139
39
Otsu 13
1940-6
1943-3
48+
48
38
1942-6
1943-9
130
42
Yo 11
1942-9
1943-11
85
37
39
1943-1
1944-1
165
50
40
1943-6
1944-6
185
?
41
1943-9
1944-7
323
?
42
1944-3
1945-2
466
?

References

Bradley et al. (1992)

Drea (2009)

Ellis (1995)

Francillon (1979)

Handbook on Japanese Military Forces (1944; accessed 2010-9-26)

Hata et al. (1989, 2002)

"History of Imperial General Headquarters, Army Section " (1959; accesssed 2012-11-10)

Madej (1981)
Molesworth (2008)

Morton (1953)

Pettibone (2007)

Rottman (2002, 2005)

Rottman and Takizawa (2005)

Victory Games (1985)

Willmott (1982)



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