Japanese mobile division TO&E

[BobTheBarbarian]

Hi,

At the end of World War II, the Japanese Army activated a number of high-quality "mobile divisions" to be used as reserves during the expected battle on the Home Islands. With few exceptions, these were numbered in the 200-series (i.e, 201st, 202nd, 205th, etc.), consisted of the best, most qualified remaining personnel, and possessed a comparatively high degree of firepower. From what I have gathered, their organization followed a pattern, that is, three infantry regiments, a field or mountain artillery regiment, a mortar regiment, and an automatic cannon company along with the remaining liaison and logistics units - total strength was about 20,000 to 22,000 people. However, information beyond that is lacking. Particularly, I'm trying to find out:

1. What was the composition of the "mortar regiment?" US intelligence handbooks have no data on the subject.

2. What was the composition of the automatic cannon company? I assume it used Type 98 20mm cannons, but how many?

3. Were these divisions more consistent with "permanent" (Type A) divisions/Ko-Shidan or "temporary" (Type B) divisions/Otsu-Shidan in organization, armament, and fighting power? Approximately how many battalion, regimental, and anti-tank guns did they have? Did their field artillery regiment more consist of 75mm and 105mm or 105mm and 150mm guns?

Thanks.

[Eugen Pinak]

1. What was the composition of the "mortar regiment?"

2 battalions x 3 companies of 6 120-mm mortars each. Total 36 mortars.

2. What was the composition of the automatic cannon company?

According to L. Ness' "Rikugun", it had automatic cannon battalion x 3 batteries of only 2 20-mm AA guns each.

Approximately how many battalion, regimental, and anti-tank guns did they have?

As per TOE: 0 battalion, 12 regimental, and 12 anti-tank guns. Plus other heavy weapons, of course. But reality was often different.

Did their field artillery regiment more consist of 75mm and 105mm or 105mm and 150mm guns?

Half had artillery regiment of 24 75mm guns and 12 105mm howitzers. Half had mountain artillery regiment of 24 75mm mountain guns.

[BobTheBarbarian]

Thanks for the numbers.

2 battalions x 3 companies of 6 120-mm mortars each. Total 36 mortars.

Surprised they are all 120mm. No 81mm or 90mm mortars? Still, that's a formidable lineup at medium range.

According to L. Ness' "Rikugun", it had automatic cannon battalion x 3 batteries of only 2 20-mm AA guns each.

About what I expected.

As per TOE: 0 battalion, 12 regimental, and 12 anti-tank guns. Plus other heavy weapons, of course. But reality was often different.

A complete absence of 70mm Type 92 howitzers? Though, I suppose the mortars more than make up for it.
So if I understand correctly, each regiment had 12 75mm howitzers and 12 anti tank guns (suggesting about 40 AT and 36 regimental pieces for the division)?

Half had artillery regiment of 24 75mm guns and 12 105mm howitzers. Half had mountain artillery regiment of 24 75mm mountain guns.

So not as much firepower as the Type A division then - mountain artillery regiments usually contained 36 pieces as well.

[Eugen Pinak]

2 battalions x 3 companies of 6 120-mm mortars each. Total 36 mortars.

Surprised they are all 120mm. No 81mm or 90mm mortars?

No. Even battalions were to receive only 120mm mortars, though in real life they had to live with 81mm ones.

So if I understand correctly, each regiment had 12 75mm howitzers and 12 anti tank guns (suggesting about 40 AT and 36 regimental pieces for the division)?

12 75mm guns and 12 47mm ATGs are for the whole division.

[wdgysin]

The figures Mr Pinak has given are for the second mobilization 'wave' mobile divisions which consisted of 201, 202, 205, 206, 209, 212,
214, & 216 in the 200 series divisions. The third wave divisions contained even less equipment than the second, as the empires resources
were growing ever thinner. The third wave mobile divisions were the 224, 230, 231, 234, 222, 225, & 229. They contained 12 70mm infan-
try howitzers in each regiment (4 per battalion) and the regimental gun companies contained 6 75mm guns, making a division total of 36
70 mm howitzers and 18 75mm guns. The only artillery unit in the division was a mortar battalion with 18 120mm mortars. The Japanese
had dropped the field artillery regiment, rapid fire gun(AT) battalion, and machine cannon battalion from the second wave mobile divisions
and downgraded the mortar regiment to a battalion for the third wave mobile divisions. This comes from Rikugun Vol I as well. It is the
best source for information (in english) on the division structures throughout the war as well as the different types of divisions (A, B, Spec-
ial, Security, Ocean, Coastal, Mobile and their variations (of which there were many).

[Eugen Pinak]

The figures Mr Pinak has given are for the second mobilization 'wave' mobile divisions which consisted of 201, 202, 205, 206, 209, 212, 214, & 216 in the 200 series divisions. The third wave divisions contained even less equipment than the second, as the empires resources were growing ever thinner. The third wave mobile divisions were the 224, 230, 231, 234, 222, 225, & 229.

I doubt this divisions can be called high-quality. Yes, they were also mobile divisions, but "high-quality" was certainly not in their description.

[BobTheBarbarian]

The figures Mr Pinak has given are for the second mobilization 'wave' mobile divisions which consisted of 201, 202, 205, 206, 209, 212,
214, & 216 in the 200 series divisions. The third wave divisions contained even less equipment than the second, as the empires resources
were growing ever thinner. The third wave mobile divisions were the 224, 230, 231, 234, 222, 225, & 229. They contained 12 70mm infan-
try howitzers in each regiment (4 per battalion) and the regimental gun companies contained 6 75mm guns, making a division total of 36
70 mm howitzers and 18 75mm guns. The only artillery unit in the division was a mortar battalion with 18 120mm mortars. The Japanese
had dropped the field artillery regiment, rapid fire gun(AT) battalion, and machine cannon battalion from the second wave mobile divisions
and downgraded the mortar regiment to a battalion for the third wave mobile divisions. This comes from Rikugun Vol I as well. It is the
best source for information (in english) on the division structures throughout the war as well as the different types of divisions (A, B, Spec-
ial, Security, Ocean, Coastal, Mobile and their variations (of which there were many).

I was about to ask this question; thanks for the preemptive answer. So it seems that the best they had were only about 84 tube artillery pieces (excluding 50mm grenade dischargers and AT guns) per division. Still better than the 66 (minus AT) in the Standard Type B division, but extremely lacking in anti-tank weaponry - even the Type B division had 22 anti-tank guns while the Type A division had 40. I suppose in this case the deficiency might be made up by supplementing Type 4 70mm rocket launchers, of which there were several thousand in Japan at that point. Were there any issued to divisional units, and if not, were there plans to do so and on what numerical basis?

The original source for the quality of the mobile divisions was D.M. Giangreco, "Hell to Pay: Operation Downfall and the Invasion of Japan" pp. 70-71. He states that after the First Stage mobilization of 18 coast defense divisions in February 1945, eight "very high quality" 200-series assault divisions were activated on 2 April. He does note that of the 19 further divisions activated during the "Third Stage," neither the coastal defense nor assault divisions were up to standard for either quality of personnel or equipment. Particularly, some of the later coastal divisions lacked artillery and instead were temporarily given heavy mortars so they could be deployed quickly in the event of an early invasion of Kyushu.

This, however, brings me to another question: in the text, the "First Stage" coastal defense divisions are described as being "strongly reinforced with artillery" to a degree that is implied to be higher than that of the mobile divisions. What kind of weapons did these divisions have, and is this description accurate or exaggeration?

[Wellgunde]

Please keep in mind that the organization tables in the Japanese mobilization plans were targets only. They do not reflect the actual state of mobilization within the new divisions nor do they show if substitutions in equipment were made. If you are interested in the actual composition of these units at the end of the war, there are a number of ways to proceed.
1. The General Staff Unit Strength Tables. These show changes to a unit's organization and are available at NARA and probably on JCAR as well.
2. 1st Demobilization Bureau Delivery Reports. These were submitted to SCAP and show the numbers and types of equipment and weapons destroyed, surrendered, or rendered ineffective. Available at NARA and JCAR.
3. Occupation Reports. Each U.S. Army corps and the Marine V Amphibious Corps were required to report to either Sixth or Eighth Army the status of the Japanese Occupation. The G2 (intelligence) sections of these reports give detailed information on the Japanese Order of Battle and equipment reports similar to number 2 above. These are available at NARA.

[wdgysin]

The first wave coastal divisions consisted of the 140, 144, 145, 146, 147, 150, 152, 154, 155, 156, &
160 activated in February 1945 and the 142, 143, 151, 153, & 157 activated in early April 1945. The divis-
ions all consisted of a Division Headquarters, three static infantry regiments, one mobile infantry regiment,
a field artillery battalion (or rocket gun battalion), a rapid fire gun (ATk) battalion, a division signal unit, a
transport regiment, a division ordnance duty unit, and a division field hospital.

Artillery weapons in the three static infantry regiments consisted of 6 70mm infantry howitzers per bat-
talion (2 per infantry company) and 6 47mm rapid fire guns in each batallions gun company. This gives a
total of 18 70mm howitzers and 18 47mm rapid fire guns per regiment plus 4 37mm rapid fire guns in each
regimental rapid fire gun company. The one mobile infantry regiment (to be held in reserve for counterat-
tack) with only two battalions contained 6 81mm mortars in each battalion and two regimental gun compan-
ies each with 4 75mm mountain guns. This gives the regiment a total of 12 81mm mortars and 8 75mm
mountain guns. So for the four regiments of the division we get 54 70mm inf guns, 54 47mm RF guns, 12
37mm RF guns, 8 75mm mtn guns and 12 81mm mortars. The Division also contained a RF gun battalion of
12 47 mm RF guns and a field artillery battalion of 8 75mm field guns and 4 105mm howitzers. In the 142,
143, 145, 150, 151, & 157 Divisions, the field artillery battalion was replaced by a rocket gun battalion of 12
200mm rocket launchers. As Wellgunde pointed out, the numbers are only the organizational figures and the
actual figures would probably contain substitutions or what was available at the time. Again, all these figures
come from Rikugun Vol I by Leland Ness.

The 3rd wave coastal divisions were much leaner and consisted of the 303, 312, 320, 321, 344, 354 activat-
ed in May 1945, the 308, & 351 activated in June, and the 316, 322, & 355 activated in July. Each had a division
HQ, three infantry regiments, a rocket gun battalion (field artillery battalion in the 321 & 322 divisions), a div
signal unit, a div engineer unit, a div transport unit and a div field hospital.The three static infantry regiments
contained 9 37mm RF guns (3 per infantry batalion gun platoon) so 27 per division. The rocket gun battalion
had 36 200mm launchers in all but two of the divisions with the 321 & 322 divisions having a FA battalion of 8
75mm mtn guns and 4 105mm howitzers. You can see just how threadbare these divisions had become. Although
all of the divisions had been formed, it is unclear how many were completed and which ones were still forming
and what state each was in. The references Wellgunde gives may be a source which might clarify this as, being
a non-Japanese speaker, I am forced to rely on google translate, which doesn't do much for JCARS photographic
documents.

[Eugen Pinak]

... but extremely lacking in anti-tank weaponry - even the Type B division had 22 anti-tank guns while the Type A division had 40.

Type B division usually had 8 ATG while Type A division had 14 to 20 ATG.

I suppose in this case the deficiency might be made up by supplementing Type 4 70mm rocket launchers, of which there were several thousand in Japan at that point. Were there any issued to divisional units, and if not, were there plans to do so and on what numerical basis?

No data in the sources I knew. Only "Rikugun" says, that in 209th division each regimental pioneer company was turned into RPG company of 3 platoons x 10 Type 4 70mm rocket launcher each.

This, however, brings me to another question: in the text, the "First Stage" coastal defense divisions are described as being "strongly reinforced with artillery" to a degree that is implied to be higher than that of the mobile divisions. What kind of weapons did these divisions have, and is this description accurate or exaggeration?

This is not correct. "First Stage" coastal defense divisions were larger (4 infantry regiments instead of 3 in "mobile" divisions), but they only had 1 or even 0 artillery battalions. The only reinforcement versus standard infantry organization was an increase of number of infantry guns and addition of obsolete 57mm static(?) tank guns - neither mattered much in overall weight of firepower.

[Akira Takizawa]

> 57mm static(?) tank guns

They will be pillboxes converted from 57mm gun turret of Type 89 Medium Tank.

Type 89 Medium Tank turret used as pillbox on Chichi-jima
https://plaza.rakuten.co.jp/zeong/diary/201010220000/

Taki

[BobTheBarbarian]

The first wave coastal divisions consisted of the 140, 144, 145, 146, 147, 150, 152, 154, 155, 156, &
160 activated in February 1945 and the 142, 143, 151, 153, & 157 activated in early April 1945. The divis-
ions all consisted of a Division Headquarters, three static infantry regiments, one mobile infantry regiment,
a field artillery battalion (or rocket gun battalion), a rapid fire gun (ATk) battalion, a division signal unit, a
transport regiment, a division ordnance duty unit, and a division field hospital.

Artillery weapons in the three static infantry regiments consisted of 6 70mm infantry howitzers per bat-
talion (2 per infantry company) and 6 47mm rapid fire guns in each batallions gun company. This gives a
total of 18 70mm howitzers and 18 47mm rapid fire guns per regiment plus 4 37mm rapid fire guns in each
regimental rapid fire gun company. The one mobile infantry regiment (to be held in reserve for counterat-
tack) with only two battalions contained 6 81mm mortars in each battalion and two regimental gun compan-
ies each with 4 75mm mountain guns. This gives the regiment a total of 12 81mm mortars and 8 75mm
mountain guns. So for the four regiments of the division we get 54 70mm inf guns, 54 47mm RF guns, 12
37mm RF guns, 8 75mm mtn guns and 12 81mm mortars. The Division also contained a RF gun battalion of
12 47 mm RF guns and a field artillery battalion of 8 75mm field guns and 4 105mm howitzers. In the 142,
143, 145, 150, 151, & 157 Divisions, the field artillery battalion was replaced by a rocket gun battalion of 12
200mm rocket launchers. As Wellgunde pointed out, the numbers are only the organizational figures and the
actual figures would probably contain substitutions or what was available at the time. Again, all these figures
come from Rikugun Vol I by Leland Ness.

The 3rd wave coastal divisions were much leaner and consisted of the 303, 312, 320, 321, 344, 354 activat-
ed in May 1945, the 308, & 351 activated in June, and the 316, 322, & 355 activated in July. Each had a division
HQ, three infantry regiments, a rocket gun battalion (field artillery battalion in the 321 & 322 divisions), a div
signal unit, a div engineer unit, a div transport unit and a div field hospital.The three static infantry regiments
contained 9 37mm RF guns (3 per infantry batalion gun platoon) so 27 per division. The rocket gun battalion
had 36 200mm launchers in all but two of the divisions with the 321 & 322 divisions having a FA battalion of 8
75mm mtn guns and 4 105mm howitzers. You can see just how threadbare these divisions had become. Although
all of the divisions had been formed, it is unclear how many were completed and which ones were still forming
and what state each was in. The references Wellgunde gives may be a source which might clarify this as, being
a non-Japanese speaker, I am forced to rely on google translate, which doesn't do much for JCARS photographic
documents.

Thanks for the info - the exhaustion of equipment stocks is pretty clear with the difference in mobilization waves. I will see what I can find with NARA, though their "previews" don't seem to offer much so I'm a bit wary of spending money on them.

No data in the sources I knew. Only "Rikugun" says, that in 209th division each regimental pioneer company was turned into RPG company of 3 platoons x 10 Type 4 70mm rocket launcher each.

Thanks for the data about the rockets, I will try and keep looking to see what I can find.

Type B division usually had 8 ATG while Type A division had 14 to 20 ATG.

This seems far too little. According to the US Army's TM-E-30-480 "Handbook on Japanese Military Forces," the Type B (standard) division had 6 AT guns per regiment (subtotal 18) plus another 4 in the reconnaissance unit, while the strengthened Type A division had 12 per regiment and 4 in the recon unit for a total of 40. Even this was rather low compared to, say, a first-rate German infantry division from 1941, which nominally had up to 72 AT weapons 37-50mm in caliber in its TO&E.

[Eugen Pinak]

> 57mm static(?) tank guns

They will be pillboxes converted from 57mm gun turret of Type 89 Medium Tank.

Type 89 Medium Tank turret used as pillbox on Chichi-jima
https://plaza.rakuten.co.jp/zeong/diary/201010220000/

Taki

Thank you for the information!
I'm really surprised, that those turrets were made non-rotating.

[Eugen Pinak]

I will see what I can find with NARA, though their "previews" don't seem to offer much so I'm a bit wary of spending money on them.

Access to docs on JACAR is free - but those are mostly in Japanese.

Type B division usually had 8 ATG while Type A division had 14 to 20 ATG.

This seems far too little. According to the US Army's TM-E-30-480 "Handbook on Japanese Military Forces," the Type B (standard) division had 6 AT guns per regiment (subtotal 18) plus another 4 in the reconnaissance unit, while the strengthened Type A division had 12 per regiment and 4 in the recon unit for a total of 40. Even this was rather low compared to, say, a first-rate German infantry division from 1941, which nominally had up to 72 AT weapons 37-50mm in caliber in its TO&E.

Yes, I know that. But Japanese TOEs present different picture. BTW, later US intelligence handbooks on Japanese Military Forces also corrected their view of IJA divisions.

[Wellgunde]

The references Wellgunde gives may be a source which might clarify this as, being
a non-Japanese speaker, I am forced to rely on google translate, which doesn't do much for JCARS photographic
documents.

The "delivery reports" are hit and miss. They come in three flavors: English only, Japanese only, and English and Japanese.

According to the US Army's TM-E-30-480 "Handbook on Japanese Military Forces," ...

TME-30-480 was way behind the power curve in promulgating up to date information. A better reference on Japanese TOE's is SWAPA's Organization of the Japanese Ground Forces dated 15 Aug 45. This can be found at NARA but it is also available from AFHRA on reel/DVD 9154 ($35).