Okinawa Wargame

Discussions on all aspects of the Japanese Empire, from the capture of Taiwan until the end of the Second World War.
Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Okinawa Wargame

Postby Wargames » 02 Sep 2017 02:43

I've been considering making up an Okinawa war game. The question I dealt with today was what would be the starting Japanese forces? There are way too many Japanese and Boeitai personnel that are "useless". Looking at the LMG, HMG, and 50mm mortars available I found I could equip an extra ten battalions (11,000 men) beyond the initial 23 or so of the "2 and 1/2 divisions". Due to their lack of training they would only be available as replacements. However, they would be Japanese soldiers and not Navy sailors or native conscripts and so likely capable. Does this sound right?
Units like the Specially Established Brigades and seven independent battalions would be gone.

There would still be Admiral Ota's force with some 9,000 men and 252 MG's but with no training they work out to about 2,000 IJA troops. They start in the game. Also there are the A/A battalions. Can those 75mm A/A guns be used as A/T guns?

The 320mm "spigot" mortars have lousy range and poor effect. Include them or forget? Make them moveable or fixed?

The US had huge numbers of "non-battle" casualties (combat fatigue). How do I factor this into the game? So many per turn? Beginning after how many days? Do some come back?

I don't have much information on the Shuri line. Can someone give me some map guides? Right now it kooks like there's only two lines to cross to reach Shuri from the north (three to take Shuri) and one from the south (two to take Shuri.).

So far, map is only half the island.

Any other suggestions I should consider? Like rain? What is it's effect if any? Can Japanese use counter battery artillery fire (I don't see where they did that.)? US did.

US has option to land one division behind Japanese lines. Ships and aircraft have no effect on Shuri line although tanks do. Game is battalion level. Japanese cannot stack battalions on Shuri line. Japanese are also limited in how many times their artillery can fire (twenty bombardments) and then all guns go silent due to lack of ammo. All opinions welcome.


Posts: 91
Joined: 18 Nov 2015 02:44
Location: Charlotte

Re: Okinawa Wargame

Postby BobTheBarbarian » 02 Sep 2017 06:48

According to Appleman ["Okinawa, the Last Battle" ch. IV], the primary combat power of the Jap 32nd Army (Corps) consisted of the 24th and 62nd Divisions together with the 44th IMB. The 62nd Division (Type C) which had fought in China possessed most of Ushijima's veteran troops and had 8 infantry battalions (14,000 men) but no divisional artillery, whereas the 24th (Type B) had 9 battalions (3 per regt. at reduced strength) for a manpower total of 15,000. The 24th's divisional artillery regiment included 16 105mm Type 91, 12 150mm Type 4, and 8 75mm Type 95 guns (36 pieces total).

All Japanese units on Okinawa, particularly the 44th IMB and 24th Division, relied considerably on local conscripts to fill out their ranks.The former had been almost completely destroyed by submarines en route to the island in June 1944, leaving only 600 survivors who were to form the nucleus of the reconstituted unit that faced Gen. Buckner's Tenth Army. Comprising the 2nd Infantry Group and the 15th Mixed Regiment, after receiving replacements from Kyushu and local draftees its strength totalled approximately 6,000, but without a full compliment of equipment.

In addition to the above, General Ushijima ordered the conversion of seven 'sea-raiding' battalions (originally intended to crew suicide boats) into 600 man infantry battalions to fill in the gap left by the withdrawal of the 9th Division. Also present on the island were the 27th Tank Regiment (750 men), 4 machine cannon battalions (1,600 men), an independent mortar regiment (600 men), 2 light mortar battalions (1,200 men), 4 AA battalions (2,000 men), 3 machine gun battalions (1,000 men), 3 independent antitank battalions and 4 AT companies (1,600 men), about 22,000 to 23,000 service troops, 20,000 Boeitai Okinawan laborers and militiamen, and 10,000 IJN personnel under Admiral Minoru Ota's Okinawa Naval Base Force, of whom only 200 had anything more than basic combat training. The total manpower under Ushijima's command was approximately 100,000, of whom Japanese personnel accounted for 70,000 to 80,000 while the rest were Okinawans.

Weapons of the 32nd Army included a very high proportion of automatic weapons and mortars relative to TO&E strength as well as a large quantity of various explosives. The total list of major pieces included 287 field guns 70mm in caliber or greater, of which 52 were 150mm howitzers, 12 were 150mm cannons (Type 89), 170 were 70 and 75mm field pieces, and the remaining 53 were 105mm, 120mm, or >150mm in caliber. There were also a further 72 x 75mm AA guns, 54 x 20mm cannons, 96 x 81mm mortars, 24 x 320mm mortars, 1,100 50mm mortars, 52 x 47mm AT, 27 x 37mm AT, 333 HMGs, 1,208 LMGs, 14 medium and 13 light tanks. All artillery pieces outside the divisional TO&Es were under the central control of the 5th Artillery Command (3,200 personnel).

Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Re: Okinawa Wargame

Postby Wargames » 02 Sep 2017 23:01

Japanese Order of Battle
Unit Strength
Thirty-second Army Troops
Headquarters 1,070
Ordnance Depot 1,498
Ordnance Duty Unit 150
Field Freight Depot 1,167
36th Signal Regiment 1,912
Okinawa Army Hospital 204
27th Field Water Purification Unit 244
Well Digging Unit 34
Defense Construction Unit 108
7th Fortress Construction Duty Company 322
2d Field Construction Duty Company 366
24th Infantry Division
Headquarters 267
22d Infantry Regiment 2,796
32d Infantry Regiment 2,870
89th Infantry Regiment 2,809
42d Field Artillery Regiment 2,321
24th Reconnaissance Regiment 346
24th Engineer Regiment 777
24th Transport Regiment 1,158
Signal Unit 275
Decontamination Training Unit 77
Ordnance Repair Unit 57
Veterinary Hospital 11
Water Supply and Purification Unit 241
1st Field Hospital 174
2d Field Hospital 181
62d Infantry Division
Headquarters 65
63d Brigade Headquarters 129
11th Independent Infantry Battalion 1,091
12th Independent Infantry Battalion 1,085
13th Independent Infantry Battalion 1,058
14th Independent Infantry Battalion 1,085
273d Independent Infantry Battalion 683
64th Brigade Headquarters 121
15th Independent Infantry Battalion 1,076
21st Independent Infantry Battalion 1,080
22d Independent Infantry Battalion 1,071
23d Independent Infantry Battalion 1,089
272d Independent Infantry Battalion 683
Engineer Unit 255
Signal Unit 359
Transport Unit 300
Field Hospital 371
Veterinary Hospital 22
44th Independent Mixed Brigade Headquarters 63
2d Infantry Unit 2,046
15th Independent Mixed Regiment 1,885
Artillery Unit 330
Engineer Unit 161
5th Artillery Command Headquarters 147
1st Medium Artillery Regiment (-) 856
23d Medium Artillery Regiment 1,143
7th Heavy Artillery Regiment 526
100th Independent Heavy Artillery Battalion 565
1st Independent Artillery Mortar Regiment (-) 613
1st Light Mortar Battalion 633
2d Light Mortar Battalion 615

Unit Strength
21st Antiaircraft Artillery Command
Headquarters 71
27th Independent Antiaircraft Artillery Bn 505
79th Field Antiaircraft Artillery Battalion 513
80th Field Antiaircraft Artillery Battalion 517
81st Field Antiaircraft Artillery Battalion 514
103d Independent Machine Cannon Battalion 336
104th Independent Machine Cannon Battalion 338
105th Independent Machine Cannon Battalion 337
Machine Gun Units
3d Independent Machine Gun Battalion 340
4th Independent Machine Gun Battalion 344
14th Independent Machine Gun Battalion 334
17th Independent Machine Gun Battalion 331
Antitank Units
3d Independent Antitank Battalion 363
7th Independent Antitank Battalion 353
22d Independent Antitank Battalion 402
32d Independent Antitank Company 144
11th Shipping Group
Headquarters 100
7th Shipping Engineer Branch Depot 600
23d Shipping Engineer Regiment 850
26th Shipping Engineer Regiment (-) 550
5th Sea Raiding Base Headquarters 42
1st Sea Raiding Squadron 104
2d Sea Raiding Squadron 104
3d Sea Raiding Squadron 104
26th Sea Raiding Squadron 104
27th Sea Raiding Squadron 104
28th Sea Raiding Squadron 104
29th Sea Raiding Squadron 104
1st Sea Raiding Base Battalion 886
2d Sea Raiding Base Battalion 874
3d Sea Raiding Base Battalion 877
26th Sea Raiding Base Battalion 908
27th Sea Raiding Base Battalion 897
28th Sea Raiding Base Battalion 900
29th Sea Raiding Base Battalion 900
49th Line of Communication Sector
Headquarters 202
72d Land Duty Company 508
83d Land Duty Company 496
103d Sea Duty Company 711
104th Sea Duty Company 724
215th Independent Motor Transport Company 181
259th Independent Motor Transport Company 182
Engineer Units
66th Independent Engineer Battalion 865
14th Field Well Drilling Company 110
20th Field Well Drilling Company 110
19th Air Sector Command
Headquarters 41
29th Field Airfield Construction Battalion 750
44th Airfield Battalion 377
50th Airfield Battalion 360
56th Airfield Battalion 380
3d Independent Maintenance Unit 120
Makoto 1st Maintenance Company 90
118th Independent Maintenance Unit 100
6th Fortress Construction Duty Company 330
Detachment, 20th Air Regiment 27
10th Field Meteorological Unit 80
26th Air-Ground Radio Unit 117
46th Independent Air Company 132
1st Branch Depot, 5th Field Air Repair Depot 130
21st Air Signal Unit 310
Okinawa Branch, Army Air Route Department 359
223d Specially Established Garrison Company 200
224th Specially Established Garrison Company 200
225th Specially Established Garrison Company 200
27th Tank Regiment 750
Army Unit Total 66,636

Okinawa Base Force (Headquarters, Coast Defense, and Antiaircraft Personnel) 3,400
27th Motor Torpedo Boat Squadron 200
33d Midget Submarine Unit 130
37th Torpedo Maintenance Unit 140
Torpedo Working Unit 130
81mm Mortar Battery 150
Oroku Transmitting Station 30
Naha Branch, Sasebo Naval Stores Department 136
Naha Branch, Sasebo Transportation Department 136
Naha Navy Yard, Sasebo Naval Base 53
Oroku Detachment, 951st Air Group 600
Nansei Shoto Air Group 2,000
226th Construction Unit 1,420
3210th Construction Unit 300
Navy Unit Total 8,825

502d Special Guard Engineer Unit 900
503d Special Guard Engineer Unit 700
504th Special Guard Engineer Unit 700
Blood-and-Iron-For-The-Emperor-Duty-Unit 750
Boeitai Assigned to the Army 16,600
Boeitai Assigned to the Navy 1,100
Students 600
Regular Conscripts Not Included Under Army Units 2,000
Okinawan Total 23,350

Grand Total (Rounded Out)
Army Units 67,000
Navy Units 9,000
Okinawans 24,000
Japanese Strength On Okinawa 100,000

Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Re: Okinawa Wargame

Postby Wargames » 03 Sep 2017 09:19

Some preliminary results from the game:

1) American naval and aircraft bombardment have no effect whatsoever. However, no Japanese unit should be caught in the open. This is a MUST.

2) The Japanese calling the 62nd Division's battalions "independent" is quite accurate. Each one had little or no regard for what the other was doing. 62nd's HQ mostly watched as the independent battalions made their own decisions on their own terrain and then HQ responded (if at all) as the situation unfolded. The 62nd trusted their pillboxes (which they built) over their outside commanders. The 62nd's idea of an offensive was to take back a lost position. The IJA preached defense was just something you did when not on the offense yet the 62nd never went onto the offense. Neither did they believe in retreat. However there was a problem with independent battalions. An independent battalion designed and built its own front to hold it's own men and no more. The IJA could not add a second battalion to their position with any benefit. It did not double the number of pillboxes or firing ports. The prepared position fit one battalion and no more.

3) I had to standardize Japanese infantry battalions for replacement purposes but they were standardized along the 62nd's lines so the results along the 62nd's front were pretty much historical. They ended up with nine battalions instead of ten.

4) The Japanese built more fortifications than they had troops to man. At any one time about half sat empty. It depended upon where the US attacked.

5) The ability or threat of the US landing in their rear prevented the Japanese from fully manning the Shuri line. The US casualties would have been massive if they did. Yet there appears to have been only four battalions of the 62nd on this line initially which could have held all nine across the front. This lack of troops on the front makes Kakazu the most critical point and is why the Japanese defended it the longest and why it inflicted so many US casualties. Unfortunately for them, as per item #2 above, they were limited to defending it with a single battalion. Still, it was a good one and in the game it's a good one too. But there's no help.

6) A typical US attack was tanks and infantry with artillery support (said artillery not including ships or aircraft). On day one, mines stopped the tanks (just one mined tank could stop an entire column) but the infantry advanced into what can best be described as Hell. If you raised your head you could be hit from any of three different directions. The Japanese would let one group advance over open ground and then open up on those behind, slaughtering them. Although the group that made it across reached their objective they couldn't take it or get back so, by nightfall they retreated as the Sherman mined tanks were being recovered. Next day (day 2) again came the tanks and infantry with artillery support but now with the minefield cleared. Only now they ran into A/T guns (satchel bombs are not included in the game) and the tanks were stopped again. So the infantry advanced in a repeat of day one on day two including the subsequent retreat at night. Day three here came the tanks and infantry again and the now known A/T guns knocked out. With no more A/T guns US Shermans knocked out pillbox after pillbox. Usually on day three you could pretty much wipe out the Japanese.

7) However, the Japanese pillboxes allowed them to be entered from behind, either to escape or reinforce. Thus, on day four the pillboxes were reoccupied and a surface counter attack got rid of the US troops standing outside the openings. This required a fifth day attack (no A/T mines now) by the US to take a position (or not) actually reached the first day.

8) Sometimes this fifth day attack worked and sometimes it didn't. If it worked, the US gained 1,000 yards in five days which was a very slow slog.
According to the game, if it didn't work though another problem arose. US troops had seen Japanese troops fight to the last man on day three and now they had to fight them all over again, full force, day five. This was not normal. This was insane. It was fanaticism. The human mind will try and make sense of nonsense even if it has to hallucinate to do so. This is my first wargame where I had to include "combat fatigue" (PTSD) as a combat factor. If the battle went past day five for the position, for every two Americans killed or wounded a third dropped out as mentally unfit to deal with the situation. As a result, US casualties jumped 50%.

9) This is also the first time I ever had to differentiate between artillery support and bombardment. In support Japanese artillery fired on pre-ranged positions in front of their defenders (The 320mm spigot mortar attacks.). This was defensive and does not require much ammunition expenditure. On May 3-4 the Japanese opened with an offensive bombardment which requires LOTS of ammunition. They had to roll their guns out and leave them outside their caves too long to perform this function. As a result they were subjected to counter artillery fire and they LOST that exchange. Entire battalions of Japanese artillery were destroyed. In this game, the Japanese just cannot come out of underground. No matter what.

10) Both sides had replacement troops, the US about 22,000. I use 13,000 for the Japanese. This could be argued to be an arbitrary number for the Japanese but one has to use some number. The IJA had enough weapons and soldiers to equip virtually exactly that number of replacements on hand. No combats show this wasn't feasible. The idea that the Japanese had 100,000 defenders on the island though is an absolute fantasy. They were caught with air and navy support units on hand along with labor forces and all without a gun. If the island actually had 100,000 defenders the US never would have attacked. There would have been at least six divisions versus two and 1/3.

I'm sharing these results because I use sites like this to develop the necessary historical force information to develop an accurate game (And I'm sure I'm not the first.). It is my usual intent to look for a conflict in which either side can win (North Africa, Midway, Guadalcanal, Port Moresby, Stalingrad, etc.). In this case Japanese victory is impossible. I have to compare it to the Germans defense of Italy. Pay for every yard until the war ends. That's the best you'll get. For the Japanese player to even have one battalion left in existence on June 22nd is a victory (Although I haven't gotten that far.).

But possibilities to survive beyond June 22 do exist. I see I have three battalions of Type 98 20mm machine cannons. I don't even know how many are in a battalion but they have a 5,000 yard range with armor piercing ammo which could not be good on US landing barges. I have 75mm A/A guns too but don't know how to use them. Any help or suggestions is appreciated.

Have a good day!

Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Re: Okinawa Wargame

Postby Wargames » 05 Sep 2017 04:16

Anyone know where the Japanese sited their 5th Artillery? It was supposed to be massed in a central location.

Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Re: Okinawa Wargame

Postby Wargames » 05 Sep 2017 07:39

I have now mapped out what I believe to be the Shuri line. Preliminary sources were not very accurate. For example the line is said to have begun at the narrowest part of the southern isthmus between Chatan on the west and Toguchi on the east. There is part of a natural defensive line here, extending from the east coast and running west from Atsuta to Kishaba, then SW to Atonniyo. Across the north south highway of what I believe was then route 5 (now the Okinawa Express) from Atonniya is Futerna on the Ginawon escarpment. Between Futerna and Atonniyo this dominates the express highway south. However the present route 58 (then Route1?) bypasses it to the west. I have not been there but topographical maps suggest it is not very promising. I'm thinking the US could go right past it on Route 1 (58).

To the best of my knowledge the northern most section of the Shuri Line ran from Kakuzu-Nishibaru-Kaniku-Tanabaru escarpment - Hill 178 - Skyline Ridge, a front of about 5-6,000 yards with an additional 4,000 yards protecting the flanks and to be manned by the 62nd Division. Initial evidence shows it was only manned by four battalions plus fragments of other units for possibly just five battalions. It appears to be designed to hold nine battalions, each sited independently. Due to the mutual support, Kaniku could be lost and the line still held. Although very well thought out defensively, counter-attack from this line is simply impossible. First, the line wasn't designed to hold that many men and second, the US defensive positions are quite good on the east side of the island (Up the "Express" highway) and can fire from the east on the Japanese coming up Route 1 (58) over open ground. The Japanese counter attack was either an act of desperation or insanity.

Behind the first line was the second, designed to shorten the line from a front of nine battalions to six. It appears Conical Hill was without support from Shuri HQ and drew instead up Yanabaru (24th Division). When the 24th took the line it might have been with as few as three battalions. The 62nd's new front was also designed for three battalions.

The third line wasn't really a line at but rather a position that the other battalions could fall back to, be surrounded, and make their last stand. Some Historians reference a Naha-Shuri-Yonabaru line as a "fourth" line. Technically this not a line at all but the positions do exist (The bulk of the 62nd may have been positioned here initially to aid with any landings to their south.). What the Japanese eventually used them for was to withdraw through them from the Shuri area which otherwise would have been surrounded. This "fourth" position held the way open for about a 2,000 yard wide corridor for retreat.

The Americans did notice the Japanese moving south along this corridor. There were reports of heavy rain and perhaps the US did not attempt to interfere because of it. But I have also read of 7,000 Japanese men disappearing in this retreat. A bombardment of this escape would have been disastrous as they would have been caught above ground. If not, then I'm going with those 7,000 men being Boeitai who decided to take the opportunity of the retreat to sneak off (7,000 also happens to be the number of Japanese that surrendered.).

The IJA retreated to the previous positions of the 24th Division which was not a part of the shuri Line. Although already in existence and provisioned it's possible (although I haven't mapped it up yet) that this position likely suffered from two problems. The defensive front would have been limited to about 9,000 yards which squeezes them into a very small area of the peninsula with no secondary, fall back position. Worse, the positions would have all been sited backwards (facing the sea).

They were really not a lot places left to go.

All criticisms welcome. I would be astonished if I did not make a mistake.

Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Re: Okinawa Wargame

Postby Wargames » 12 Sep 2017 06:40

Have some conflicting info. One source claims US had 800 tanks and another eight battalions (five Army and three Marine) or 400 tanks. Any help here?

Thanks in advance.

New member
Posts: 1
Joined: 10 Dec 2015 08:49
Location: chicago

Re: Okinawa Wargame

Postby diamonddave » 12 Sep 2017 22:56

Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Re: Okinawa Wargame

Postby Wargames » 13 Sep 2017 04:47

diamonddave wrote:

This site may be helpful

Thanks. I counted 7 tank battalions.

Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Re: Okinawa Wargame

Postby Wargames » 13 Sep 2017 05:52

Progress update: The game is not yet finished owing to determining movement factors of individual units for both sides. For the most part though you can, by recreating a specific period of time and the units involved, obtain a very accurate historical result. However, any two game players will deviate substantially from the historical strategy of both sides via "perfect knowledge". In 20-20 hindsight the American player will know better than to attack with tanks unsupported by infantry as well as to use way more artillery in supporting attacks while the Japanese player will avoid launching his own counteroffensives as too costly although their attack of May 3-4 is really, really tempting (If you're ever going to attack, now is the time). The Japanese player also knows the American player must land at least five division north of Shuri allowing him to preposition here accordingly. Basically, knowing the combat rules today both sides can avoid the mistakes made then. The Japanese player actually has higher daily losses when the US is prepared day one for how to attack. Yet the Japanese player also has more troops for the defense by not squandering them away on offense. Thus, the daily massacre actually intensifies for virtually the same ground gains.

The Japanese player will also be tempted to defend the Hagushi landing zones. Historically, this never happened. But, in the game, this is a distinct possibility. Japanese units are very well suited to defend against beach landings (It's their strongest point.). This changes the game entirely.

I have neither Japanese starting positions nor their movement speeds but they were very slow in reaching their positions on the Shuri Line. It's pretty much necessary for the Japanese to fight some sort of delay on the isthmus (even if only on a company level) or the Americans will actually reach the Shuri lines (at least on the east side) before the Japanese. Any help on where any units were positioned or that might help me determine their movement factor per "x" period of time would be appreciated.

Again, the IJA was designed to take on the Americans on the beaches. That a quick victory was anticipated can be seen in their ammunition supplies. To me, the 32nd Army has a three week supply of ammunition, particularly artillery. If I'm wrong on that I will gladly accept correction. It counters the concept of fighting a delaying battle and is yet another reason for the Japanese player to meet the invasion on the beaches. The battle might be over in thirty days but you will certainly kill a lot of Americans.

Posts: 318
Joined: 12 Nov 2006 20:11
Location: USA

Re: Okinawa Wargame

Postby Wargames » 14 Sep 2017 07:36

I found this site: ... 90&lang=en

It provides most Japanese artillery positions. Click on the red dots on the island.

Return to “Japan at War 1895-1945”

Who is online

Users browsing this forum: CommonCrawl [Bot], Steve E