Operation Downfall

[Mil-tech Bard]

I'm doing more reading in the same book, and the 40th ID's cannon companies had M-7's as early as the campaign on Luzon in January 1945.

So far I have read in various combat histories that the 7th ID, 37th ID, 40th ID, 77th ID and 96th ID regimental cannon companies were outfitted with either the M8 75mm or M-7 105mm SPM before Operation Olympic.

It seems that US Army Pacific theater divisions that were supported out of Hawaii or the West Coast before Leyte had their cannon company towed 105mm replaced with self-propelled guns.

The SWPA US Army Divisions in the 6th and 8th Army didn't have the working truck prime movers or the amphibious lift to move them for their cannon or anti-tank companies and used them -- operation dependent -- as either additional infantry companies or as shore/port clearance companies unloading supplies during the assault.

[Mil-tech Bard]

I have been researching On-line Operation Olympic documents at the US Army's CARL Digital library.

At this link:

http://cgsc.cdmhost.com/cdm4/document.p ... =854&REC=2

I found IX Corps "Administrative order number 1: Operation Olympic, to accompany Field Order No. 1."

It had the following information on the requirements for spare armored vehicles and artillery in Annex 4, Ordnance"

(b) Class IV:

(1) Roller Conveyor:
The issue, use and recovery of roller conveyor will be in accordance
with instructions contained in appendix C.

(2) Spare Combat Vehicles and Artillery Pieces:

Following spare combat vehicles and artillery pieces will be carried into the objective area by units, if available for issue :

(a) Field Artillery Battalions (Divisional and nondivisional):
One (1) spare gun and carriage, complete.

(b) Tank Battalions:
Each Tank Company:
1. Two (2) spare tanks, complete,
2. Each Bn. Hq. Co: One (1) spare tank, with 105mm Howitzer, complete,

(c)Tank Destroyer Battalions:
1. Each Destroyer Company:
One (1) Carriage, motor, gun, complete.
2. One (1) vehicle, armored, utility,M39, complete.

(d) Infantry Divisions:
Each Cannon Company:
One (1)Carriage, motor, 105mm Howitzer, M7, complete.

(c) All above specified spares will be turned over (complete and serviceable) to supporting ordnance maintenance companies upon arrival in the target area.

Based on this, all the infantry regiment cannon companies in the 77th, 81st and 98th Infantry Divisions in the IX Corps (there were nine) had their towed M3 105mm guns replaced with M7 105mm SPM.

The M39 was the turret-less APC/scout vehicle version of the M-18 Hellcat, so it looks like some of the M20 Scout cars were going to be displaced with M39.

The same document also lists the winter weatherization requirements in terms of anti-freeze required by vehicle type and it specifically lists the M36B1. Which is the M4A3 hulled version of the M-36 90mm tank destroyer.

The anti-freeze requirements for M4A3, the M26 Pershing and M24 Chaffee are all listed as well.

[Mil-tech Bard]

Here are more Operation Downfall on-line research links for those who have adobe PDF document viewing capability:


Administrative order number 1 covers the logistics and supply responsibilities for IX Corps for Operation Olympic, the invasion of Japan.

http://cgsc.cdmhost.com/cdm4/document.p ... =854&REC=2


Logistics Instruction No. 1 for the Olympic Operation.
History of Planning Division, ASF. Volume 11.
Headquarters, US Armed Forces Western Pacific Office of the Commanding General


http://cgsc.cdmhost.com/cdm4/document.p ... 809&REC=20




40th Infantry Division: the years of World War II, 7 December 1941 - 7 April 1946.

http://cgsc.cdmhost.com/cdm4/document.p ... 3155&REC=8




Order of battle of the United States Army ground forces in World War II: Pacific Theater of operations.
Office of the Chief of Military History, Department of the Army


http://cgsc.cdmhost.com/cdm4/item_viewe ... X=1&REC=10


Seventh Amphibious Force, command history, 10 January 1943 -- 23 December 1945.

http://cgsc.cdmhost.com/cdm4/item_viewe ... OX=1&REC=7

[Mil-tech Bard]

The following document is on-line at the CARL digital libary

ORDER OF BATTLE OF THE UNITED STATES ARMY GROUND FORCES IN WORLD WAR II
PACIFIC THEATER OF OPERATIONS

This is from page 312:

1 Jun 1945
Eighth Army directed to pass to contl of CG Sixth Army, on 1 Jul
1945, 503d Prcht RCT and the Americal, 40th, 41st, and 8lst Divs, for
purpose of regrouping American forces in the Philippines for future
opns against Japanese mainland.

20 Jun 45
Panay -Negros Occidental (VICTOR I); Cebu -Bohol -Negros Oriental
(VICTOR TL); Palawan (VICTOR Hi); and Zamboanga -Sulu Archipelago
(VICTOR IV) Opns officially terminated.

CG Eighth Army directed by GHQ AFPAC to continue missions in the
SWPA asgd by GHQ SWPA; and assist the CG's of the Sixth Army and
Far East Air Forces in staging, equipping, training, and mounting
elms of their. respective forces as later directed, or as arranged
directly between the commanders concerned, for the projected invasion
of southern Kyushu. Target date desig as 1 Nov.1945*

30 Jun 45
Mindanao (VICTOR V) Opn officially terminated.

1 Jul 45

Eighth Army reld Sixth Army of all combat and other missions on Luzon
except those pertaining to projected opns of Sixth Army and concurrently
assumed contl of Hq XIV Corps and 6th, 32d, 37th, and 38th Divs, and
of the comd desig as United States Army Forces in the Philippines,
Northern Luzon (USAFIP NL), which included the 11th, 14th, 15th, 66th,
and 121st Inf Regts. Elms of 1st Cav Div, 43rd Div, 11th A/B Div, and
158th RCT atchd to Eighth Army for opnl contl only.

* These units were to be employed for purposes of administration,
supply, and control of unorganized groups of Filipino guerrilla forces
in Dingalan Bay area south of Manila.

312

This is the first indication I have found that the 503rd Parachute infantry Regiment was going to be part of the Operation Olympic.

So we have the 112 Cavalry RCT, the 158th Inf RCT and the 503rd Parachute Inf. RCT in Olympic, a short division equivalent between them.

The best I can determine, the 503rd parachute infantry RCT was going to be in the AFPAC Reserve with the 6th ID, 7th ID and 96th Infantry Division, as it isn't in any 6th Army invasion plans.

[Mil-tech Bard]

I have found more interesting tank trivia for the Operation Olympic. I bought a copy of book number 12 in the old Ballantine's Illustrated Battle History of WW2 series, titled "OKINAWA: Touchstone to Victory." Looking square at page 150 and 151, showing a overhead picture the June 21 1945 flag raising ceremony marking the end of organized Japanese resistance. There are 12 Sherman tanks in the photo and a shadow of a 13th. I can positively identify five of them as M4A3E8 (76mm) based on a T23 type turret, a long gun barrel with a muzzle brake, and HVSS type side boards.

The Sherman shadow in the picture is of a long gun barrel with a muzzle brake.

The remaining Shermans are shown nose on with men standing on the front hull, so I cannot tell what kind of guns or turrets they have, but they all show HVSS style sideboards.

It looks like the 193rd, 711th, & 713th tank battalions remaining on Okinawa were being rearmed with M4A3E8 (76mm) issued from Hawaii Ordnance depots.

The Okinawa 10th Army garrison in August 1945 included the 7th and 27th Infantry divisions and the 20th Armored Group. The 7th ID had fought Okinawa with the 711th TB and was tagged as the earliest arriving AFPAC reserve infantry division for Olympic (X-day plus 10).

I'm going to speculate -- based on the 98th ID document I found that implemented the 10th Army action report on tank battalion organization with the attached 767th Tank battalion -- that the surviving M4 POA-CWS-H1 flame throwers of the 713th flame thrower tank battalion were going to be parceled out among the three tank tank battalions on Okinawa on the basis of an additional, provisional, two mechanized flame thrower platoon company per standard US Army TO&E.

This would give each battalion three medium tank companies, a light tank company and a two platoon provisional flame thrower tank company.

And just to make things interesting, logistically, the 193rd and 711th had six M26 Pershings each.

Unless there was some way to concentrate the surviving 75mm armed M4/M4A1/M4A3 in one battalion and the new M4A3E8(76mm) in another. You were going to see tank battalions going into combat with three different main guns, three different power trains and three different suspensions.

[Mil-tech Bard]

For those looking for more on-line Downfall documents, this is the site for you:

http://www.alternatewars.com/WW2/WW2.htm

In particular, go to these primary document source links:

Operation Downfall
http://www.alternatewars.com/WW2/Downfa ... wnfall.htm

The Japanese Plans for the Defense of Kyushu
http://www.alternatewars.com/WW2/Downfa ... Kyushu.htm

JCS 742/12: Directive on the Establishment of U.S. Army Strategic Air Forces (USASTAF) (11 July 1945)
http://www.alternatewars.com/WW2/Downfa ... 742-12.htm

JWPC 388/1: Employment of Airborne Units in Operations Against Japan (13 July 1945)
http://www.alternatewars.com/WW2/Downfa ... _388-1.htm

JCS 1120/4: British Participation in VLR Bombing of Japan (4 August 1945)
http://www.alternatewars.com/WW2/Downfa ... 1120-4.htm

JCS 1455: Requirements for Land-Based and Carrier-Based Aircraft to Accomplish the Defeat of Japan (9 August 1945)
http://www.alternatewars.com/WW2/Downfall/JCS_1455.htm

JPLC 31/18: Comparative Logistical Efficiency of Bombing Type Airplanes (11 August 1945) (6.4 MB PDF)
http://www.alternatewars.com/WW2/Downfa ... _31-18.htm

And these Secondary Document links:

Allied Order of Battle (Work in Progress) by Ryan Crierie
http://www.alternatewars.com/WW2/Downfa ... ed-OOB.htm

Pastel: Deception in the Invasion of Japan
http://www.alternatewars.com/WW2/Downfa ... Pastel.htm

[Mil-tech Bard]

Much of the weirdness of the Pacific US Army Divisions equipage is explained by the information at this link:

http://ahecwebdds.carlisle.army.mil/aww ... 1&awdid=29

Publication Date: 19450205
Creator / Author: War Department, Office of the Chief of Staff
Collection: Library
Series: Reports
Title: Minutes, Meeting of the General Council, February 5, 1945

REPORT OF THE G-4 DIVISION

2. Special Equipment for Units in Pacific Ocean Areas.©
A new procedure has been evolved in the Pacific Ocean
Areas at the request of the theater commander in an endeavor to reduce
special lists of equipment. The new procedure contemplates that
a standard special list of equipment needed in this theater by each
major type unit will be prepared by the theater commander and reviewed
by the War Department. Upon the adoption of a standard special list
for a particular unit, all units organized under that table of organization
and equipment and destined for this theater will be similarly
equipped. The result will be that all major units going to this
theater, which if organized under standard tables would require, upon
arrival in the theater, special equipment needed in the Pacific Ocean
Area only, will be properly equipped before departure for their duty
in this theater without the necessity of submitting special projects
and special lists of equipment. It is anticipated that this procedure
will reduce the necessity for special projects and special lists
of equipment, and will result in more firm requirements for the Army
Supply Program. If the trial of this procedure for a short time
within the Pacific Ocean Area is successful, it is intended to
extend this procedure to all other theaters.

[LWD]

If you guy's are going to keep up like this we should see about getting this thread moved out of the "what if" section.

[Tim Smith]

Yeah, split it from Page 2 onward.

[Mil-tech Bard]

Here is another data point for the Operation Olympic line up:


http://www.4point2.org/hist-82-p4.htm

Shortly thereafter, the 82nd CMB was regrouped in its base camp north of Manila. There was no immediate prospect of further action, as the Monsoon Season grew stronger. Much talk and preparations were under way for the impending invasion of Japan. Jeeps were seen in Manila bearing the code name OLYMPIC stenciled in white. Olympic (the invasion of the Japanese southernmost large island of Kyushu), the first step in the overall Operation DOWNFALL – the conquest of Japan – was to be preceded by the 40th Division's seizure of several small islands off the southern Kyushu coast on October 27, 1945.

With war in Europe winding down, a “point system” for rotation to the U.S. was instituted. Based on total service, months in combat and dependents, Capt. LeRoy Croxton, the battalion S-4 was to be the first officer to leave the 82nd. Butler, who had more total service and same combat time but was single, was selected as Croxton's replacement. With a promised promotion to captain, Butler agreed to stay six months after Croxton's departure and was moved up to understudy Croxton. For his first assignment, he was given a template of an LST and documents showing the space requirements for all types of vehicle to be placed in the tank well of the LST. He was directed to develop a loading plan for his long-time-combat related comrades in Company C, who were scheduled to move to Cebu in the Philippines. Once there, the company would be attached to the 43rd Division, part of the XI Corps under Lt. Gen. Charles Hall's Southern Assault Force.That large southern island of Japan, Kyushu, was to be invaded on 1 November 1945.

It looks like the 82nd Chemical Mortar Battalion was lined us as support for the XI Corps with C company (12 of 36 Mortars in a battalion) set up to support the US Army's 43rd Infantry Division.

[Mil-tech Bard]

The "Plan B"' if the A-bomb failed to get a surrender included using vast quantities of captured German nerve gas as a part of Operation Olympic.


https://www.cbrniac.apgea.army.mil/Docu ... 5_num1.pdf

History Notes
The CWS Effort to Obtain German Chemical
Weapons for Retaliation Against Japan
By Reid Kirby

Throughout the Second World War the United States
chemical warfare policy was of deterrence. The United States
had not ratified the signing of the Geneva Protocol of 1925,
and thus was not obligated to a “No First Use” policy.
Regardless, the longstanding position of the United States,
from the First World War, and reiterated in the Second World
War, was a retaliatory policy. 1

To support this policy, the Chemical Warfare Service (CWS)
maintained a credible offensive chemical capability.
Serious planning for the final invasion of Japan started in
January 1945. Known as Operation DOWNFALL, U.S.
planners sought the invasion of Kyushu Island (Operation
Olympic) in the Fall of 1945 as a strategic staging for the final
capitulating invasion of the Japanese main island (Operation
CORONET) in the spring of 1946. X-Day of OLYMPIC was
probably the largest amphibious invasion plan in history, and
the estimates of U.S. losses were anticipated to be massive
against a determined enemy that had demonstrated the will
to fight to the last man.

It was well known that the Japanese had chemical weapons,
and had used them in their invasion of China. A suspected
case had also been documented that Japanese forces, with
chemical weapons on hand, would use them against Allied
forces when faced with annihilation. 2

The chemical threat to Allied forces was real and the CWS
made serious plans for massive chemical retaliation against
Japan for Operation OLYMPIC.

Army Air Force (AAF) chemical retaliatory plans called for the
use of persistent 100-lb bombs (Mustard Gas) and
nonpersistent 500-lbs bombs (60% Phosgene filled, 40%
Cyanogen Chloride filled). The totals required in the Pacific
theater showed a massive shortage based on 120 days usage,
included an extra quantity for the first 15 days for an initial
effect.

For persistent bombs it was noted that 5,181,000 bombs were
required and only 855,000 bombs were on-hand. For
nonpersistent bombs, 776,000 were required and only
271,000 were on-hand. On-hand estimates were based on
chemical weapon stocks in the Pacific Asiatic Theater,
European Mediterranean Theater, and Zone of the Interior
stocks. With the surrender of Germany in May 1945, the
CWS contemplated augmenting its arsenal with captured
German chemical weapons to address this shortage. 3

Germany had a significant chemical arsenal of Mustard Gas
and Phosgene in 250-kg bombs. The AAF requested that
some of these bombs be returned to the United States for
immediate evaluation for carriage on U.S. aircraft and to
establish munition requirements to achieve tactical objective
similar to those described in TC 20 (26 April 1945). 4

BG Alden Waitt, then Assistant Chief CWS for field operations,
requested with the highest priority that 100 bombs each of
Mustard Gas, Phosgene, and LE-100 be returned to the
United States for evaluation. By the end of June 1945, it was
determined that the bombs were entirely suitable for
American aircraft and the agents effective. Noting unstable
boundaries and the rapid redeployment of AAF and CWS
personnel qualified to handle these weapons to the Pacific
Theater, it was recommended that as much chemical
munitions as could be located in the American army zone of
occupation and those that may be recovered from British and
Russians zones be obtained.5

LE-100, also known as Agent GA or Tabun, was one of the
new Nerve Agents discovered with the fall of Germany.
Some 23,000 tons of 250-kg bombs and 6,000 tons of 10.5-
cm shells filled with LE-100 were discovered. CWS Chief
MG William Porter requested 3,000 250-kg bomb and 5,000
10.5-cm shells filled with LE-100 be obtained with the
highest priority so that the agent could be utilized for
charging 4.2-inch chemical mortar shells for immediate
testing.6

This required the bombs to be punched and drained
at Edgewood Arsenal for filling U.S. weapons.
Field evaluation of LE-100 in 4.2-inch mortar rounds at the
Suffield Experimental Station, Canada, and in modified M70
(E46) bombs at the Army Chemical Center showed that U.S.
chemical weapons were not entirely suitable for employing
LE-100. Due to the low volatility of LE-100 and the small
size of U.S. bursters, only 10% to 20% of the agent was
liberated into an initial vapor/aerosol effect. Additionally, the
U.S. seems to have disagreed with both German and British
authorities on the potency of LE-100. Germany believed it to
have a LCt50 of 300 – 400 mg·min/m3. The British estimated
it to be about 100-mg more. The U.S. estimate was 800
mg·min/m3. LE-100 from U.S. weapons was thus considered
to have little more than a harassing effect. 7

In July 1945 the Ordnance Department noted, without
endorsement, that German 10.5-cm projectiles could be used
in U.S. 105-mm howitzers so long as the rotating bands were
turned down, or the howitzers had worn tubes. German
10.5-cm shells were 0.3-inches wider than U.S. 105-mm
shells. 8

Though the United States would not produce its own Nerve
Agent weapons until the 1950’s, the effort to obtain German
chemical weapons to augment the United States arsenal
represents the first effort to adopt the Nerve Agents.

Fortunately Operation DOWNFALL never materialized. Japan
surrendered after two nuclear strikes and the U.S. was not
compelled into chemical retaliation. The activities of the
CWS through late Spring and early Summer 1945 showed its
officers were capable of addressing emergency preparedness
and finding unorthodox solutions.
About the Author:
Mr. Kirby is a CBW technology history
scholar and subject matter expert for the United States Army
Chemical School Historical Office and Chemical Corps
Museum, Fort Leonard Wood, Missouri.

Footnotes:
1 Probably the first expression of a U.S. chemical policy was
by the Secretary of War (New York Times 21 September 1917,
p.6).

2 Memorandum by CPT William J Roberts, CWS, CW
Technical Intelligence Officer, Subject: Suspected Use of Gas
by the Japanese (HQ, 1st Cav Div, office of the AC of S, G-2,
18 February 1945) provides interviews with witnesses of two
accounts where a vomiting agent (possibly Chlorpicrin) was
apparently used by an encircled Japanese unit in Manila.

3 Memorandum by BG Alden H Wait, Assistant Chief, CWS
for field operations, Subject: Captured German Gas Filled
Bombs and Chemical Agents, dated 30 June 1945.

4 Memorandum by BG E Montgomery, Air Chemical Officer,
Subject: Captured German Gas Filled Bombs (Washington
DC: HQ Army Air Forces, 16 June 1945).

5 Op cited, 3.

6 Memorandum by MG William N Porter, Chief of Chemical
Warfare Service, Subject: Enemy Agent Munitions, LE-100
(Taboon) (Washington, DC: HQ, Army Service Forces, Office
of the Chief of Chemical Warfare Service, 29 May 1945).

7 Chemical Corps Technical Committee, “Classification of
Quick-Acting, Nonpersistent Agent GB, as a Substitute
Standard Type; Subcommittee Report V” CCTC Item 1890
(Army Chemical Center, MD, 19 May 1948): pp. V4 and V7c.

8 Letter from LTC D P Gaillard, Assistant Chief of Ordinance,
to HQ, ASF, Office, Chief of Chemical Warfare Service dated
9 July 1945.

I have a partial copy of this report:

Memorandum by CPT William J Roberts, CWS, CW
Technical Intelligence Officer, Subject: Suspected Use of Gas
by the Japanese (HQ, 1st Cav Div, office of the AC of S, G-2,
18 February 1945) provides interviews with witnesses of two
accounts where a vomiting agent (possibly Chlorpicrin) was
apparently used by an encircled Japanese unit in Manila.

That I will post later.

[Peter H]

As discussions here are more factual than "what if" I'm moving the topic to our Pacific war section.

[Mil-tech Bard]

I have been looking through the old NRSC post war report series and found a very interesting passage in COMBAT SCIENTISTS that Gen Kenney's FEAF was set to receive large numbers of AZON and RAZON bombs for the Invasion of Japan.

It appears that the USAAF's transportation bombing plan, as executed by the 5th and 7th Air Forces on Okinawa, Ie Shima, and Luzon (B-32) was going to use lots of guided bombs.

[Mil-tech Bard]

I finally tracked down the Operation Olympic TO&E for the 1st Cavalry Division (Special) in Gordon Rottman's Osprey book "World War II US Cavalry Units: Pacific Theater."

Amazon link here:

http://www.amazon.com/World-War-II-Cava ... 1846034515

The 1st Cavalry had two brigades each of two regiments.

Each Regiment had two squadrons that in turns had three troops.

Roughly, the Cavalry lacked between 1/2 and 2/3 of the crew served heavy weapons of an equivalent US Army Infantry unit. This showed up in their manpower numbers at equivalent units of organization.

From Page 13 of Rottman's book:

Cavalry ------------------Infantry
Squad - 8 men -------- Squad - 12 men
Platoon - 32 ----------- Platoon 41
Troop - 165 ------------ Company - 193
Squadron - 521 -------- Battalion - 894
Regiment - 1726 ------ Regiment 3207

The 1st Cavalry Division started off the war with lighter 75mm howitzers in two of it's four direct support artillery battalions with no general support guns. The idea being in 1941-43 that a 75mm and a 105mm battalion supported each brigade.

In 1942 the Reconnaissance squadron was split into an independent light (later medium) tank company and a mechanized cavalry troop

For the Leyte campaign one of the 75mm gun battalions got 105mm guns and in the the Luzon campaign the second 75mm howitzer battalion got 105mm guns. A 155mm howitzer battalion was attached for the Luzon campaign and it became an organic unit for the Operation Olympic.

Pages 14 and 57 tell the tale regards the 1st Cavalry Division's Operation Olympic force structure. Each Cavalry Regiment would get both of it's squadrons rebuilt to the US Infantry TO&E with the Squadron Weapon Troop getting turned into a six 105 mm cannon company. These companies would have M7 Priest SPMs. There would be no regimental anti-tank company and the Cavalry regiment's support units would be 2/3 the size of an infantry regiment, in keeping with one fewer squadron/battalion equivalent.

Going into the invasion beaches of Kyushu, the 1st Cavalry would be one infantry battalion (8 vs 9), three anti-tank companies (with either 27x57mm towed gun or 24xM-18 SPM) short compared to a regular infantry division.

On the other hand, it would have an organic medium tank company (18 M4A3 Sherman), an additional Cannon Company (6 X M7 SPM) and a whole 105mm artillery battalion more than the standard infantry division.

What Rottman also mentions, and I had not heard before -- was that the 112th Cavalry Regimental Combat team was being reorganized in the same manner as the 1st Cavalry's regiments and was to be attached to the 1st Cavalry, giving the re-enforced 1st Cavalry Division ten squadrons/battalions of cavalry troopers, a medium tank company, 5xCannon Companies, 5x105mm artillery battalions and a 155mm artillery battalion.

Based on my research to this point, it looks like every standard infantry or cavalry regiment involved in Olympic was going to have a M7 Priest armed cannon company.

[Mil-tech Bard]

This is a really great on-line document on American military preperations for the Invasion of Japan:

Report of joint air ground tests against Japanese type field fortifications (Sphinx Project) Camp Hood, Texas. Period: 6-24 July 1945.
http://cgsc.cdmhost.com/cdm4/item_viewe ... OX=1&REC=1


The things that stood out:

1) The US Military had a host of active and passive infrared night viewing devices that were coming on-line for Operation Downfall. The Alamo Scouts coming ashore on Kyushu would have "Owned the night."

2) There were a lot of tactics from the US 6th Army's Luzon campaign in the manuevers including mass Napalm strikes, AA search lights for night combat, and the use of AA guns for cave position destruction.

3) Early mortar tracking radars and sound spotting devices were going to fielded at large scale in infantry regiments.

4) The 250mm (9.75-inch) self propelled mortar made a huge impression on the evaluators in it's effects on Japanese reverse slope defense. It was going to be fielded at a rate of 2-to-4 per infantry regiment cannon company at some point during the invasion of Japan.