Transcript of "OPERATION DOWNFALL [US invasion of Japan]:  US PLANS AND JAPANESE COUNTER-MEASURES" by D. M. Giangreco, US Army Command and General Staff College, 16 February 1998

From Beyond Bushido:  Recent Work in Japanese Military History a symposium sponsored by the Center for East Asian Studies, the College of Liberal Arts and Sciences, the Office of International Programs, and the Departments of History and East Asian Languages and Cultures at the University of Kansas.  Monday, February 16, 1998.  

B. TSUTSUI:  Our next speaker, D. M. Giangreco, is an editor for the US Army's professional journal, Military Review, published by the Command and General Staff College at Fort Leavenworth, Kansas.  Giangreco has lectured widely on national security matters.  An award-winning author of five books on military and political subjects, he has also written
extensively for various national and international publications on such topics as the Falkland Islands' sovereignty question, decentralization of the Soviet Air Force command and control structure, Persian Gulf pipeline construction to circumvent the Strait of Hormuz bottleneck, and the human interface with rapidly changing technologies.   Several of his works have
been translated into French, German and Spanish.  Giangreco's most recent books have also been published in Japanese, and the next one, Dear Harry on the correspondence of "everyday Americans" with the Truman White House will be released in fall 1998 [NOTE:  see for more on DEAR HARRY].  Giangreco is also being awarded the Society for Military History's 1998 Moncado Prize for his article "Casualty Projections for the US Invasions of Japan: Planning and Policy Implications" published in the July 1997 Journal of Military History by the George C. Marshall Center and VMI.

GIANGRECO:  Thank you.  It's great to be here today.

The sudden and unanticipated conclusion of the Pacific War with the dropping of atom bombs on Hiroshima and Nagasaki was greeted with joy by all Americans, and especially by the more than three and a half million soldiers, sailors and Marines slated to invade Japan.   These forces were not only to come from the Pacific;  First Army, which had pummeled its way from Normandy to the heart of Germany, and Eighth Air Force, based in England, were on the way as well.  But morale was not good among veterans of the Ardennes, Guadalcanal, and other campaigns.  As James Jones later wrote: "What it must have been like to some old-timer buck sergeant . . . [knowing] that he very likely had survived this far only to fall dead in the dirt of
Japan's Home Islands, hardly bears thinking about."

MacArthur's staff had twice come up with figures exceeding 100,000 casualties for the opening months of combat on the southern island of Kyushu, a figure which some historians largely succeeded in contrasting favorably- and quite mistakenly- with President Harry Truman's much-derided post-war statement that Marshall had advised him at Potsdam that casualties
from both the Kyushu and Honshu invasion operations could range from 250,000 to one million men.

Truman and Marshall were intimately familiar with losses in the Pacific during the previous year:  over 200,000 casualties from wounds, fatigue and disease, plus 10,000 American dead and missing in the Marianas, 5,500 dead on and around Leyte, 9,000 dead during the Luzon campaign, 6,800 at Iwo Jima, 12,600 at Okinawa, and 2,000 killed in the unexpectedly vicious fighting on Peleliu.  Both also knew that, save for some operations around New Guinea, real casualties were routinely outpacing estimates and the gap was widening.  They also knew that while America always emerged victorious, operations often were not being completed as rapidly as planned- with all the added cost in blood and treasure that such lengthy campaigns entailed.

Leyte is a perfect example.  Leyte was to the Luzon campaign what the Kyushu invasion was to the capture of Honshu's Kanto Plain and Tokyo, a preliminary operation to create a huge staging area.  Today, we can recall MacArthur wading ashore triumphantly in the Philippines.  But what Truman and Marshall knew only too well was that MacArthur was supposed to have retaken Leyte with four divisions and have eight fighter and bomber groups striking from the island within 45 days of the initial landings.  However, nine divisions and twice as many days into the battle, only a fraction of that airpower was operational because of unexpected terrain conditions (and this on an island which the United States had occupied for over forty years).  The fighting on the ground not gone as planned.  The Japanese even briefly isolated Fifth Air Force headquarters and also captured much of the Burauen airfield complex before reinforcements pushed them back into the jungle.

Now, some historians have stated incredulously that Marshall's estimate of up to one million casualties for the invasion of Japan significantly exceeded those sustained in Europe.  But while the naval side of the Pacific War displayed the broad, sweeping moves so loved by historians, land combat in the Pacific had little in common with the maneuver warfare that went a long way toward keeping casualties comparatively low in France and the central German Plain.  The closest European commanders came after D-Day to the corps-level combat which was the stock and trade of Army and Marine divisions in the Pacific was the prolonged fighting in the Huertgen Forest and Normandy's hedgerows- close-in, infantry-intensive slugfests that produced many bodies on both sides.  It is also important to note that when they went to Potsdam, Truman and Marshall knew that total US casualties had recently exceeded the one and a quarter million mark- a number these historians find unfathomable- what's more the bulk of the losses occurred in just the previous year of fighting against Germany.

There were plenty of estimates which confidently asserted that strategic bombing, blockade, or both- even the invasion of Kyushu alone- would bring Japan to its senses, but no one was able to provide General Marshall with a convincing explanation of just how long that would take.  The millions of Americans poised to take part in the largest invasion in history, as well as those supporting them, could only stay poised for so long.   Leaders in both Washington and Tokyo knew this just as well as their theater commanders in the Pacific.  After learning of the bomb, MacArthur ignored it save for considering how to integrate the new weapon into plans for tactical operations at Kyushu and Honshu if Tokyo was not forced to the surrender table. Nimitz was of a similar mind.  On being told that the bomb would become available in August, he reputedly remarked, "In the meantime I have a war to fight."

On 29 July 1945, there came a stunning change to an earlier report on enemy strength on Kyushu.  This update set alarm bells ringing in MacArthur's headquarters as well as Washington because it stated bluntly that the Japanese were rapidly reinforcing southern Kyushu and had increased troop strength from 80,000 to 206,000 men, quote: "with no end in sight." Finally, it warned that Japanese efforts were, quote: "changing the tactical and strategic situation sharply."  While the breathless "no end in sight" claim turned out to be somewhat overstated, the confirmed figures were ominous enough for Marshall to ponder scraping the Kyushu operation altogether even though MacArthur maintained that it was still the best option available.

Now, this is particularly interesting because, in recent years, some historians have promoted the idea that Marshall's staff believed an invasion of Japan would have been essentially a walk-over.  To bolster their argument, they point to highly qualified- and limited- casualty projections in a variety of documents produced in May and June 1945, roughly half a year
before the first invasion operation, Olympic, was to commence. Unfortunately, the numbers in these documents- usually 30-day estimates- have been grossly misrepresented by individuals with little understanding of how the estimates were made, exactly what they represent, and how the various documents are connected.  In effect, it is as if someone during World War II came across casualty estimates for the invasion of Sicily, and then declared that the numbers would represent casualties from the entire Italian campaign.  Then, having gone this far, announced with complete confidence that the numbers actually represented likely casualties for the balance of the war with Germany.  Of course, back then, such a notion would be dismissed as being laughably absurd, and the flow of battle would speedily move beyond the single event the original estimates- be they good or bad- were for.   That, however, was fifty-plus years ago.  Today, historians doing much the same thing, win the plaudits of
their peers, receive copious grants, and affect the decisions of major institutions.   [Laughter.]

The limited and cautiously optimistic estimates of May and June 1945 were turned to junk by that intelligence estimate at July's end, and the situation was even more dangerous than was perceived at that time.  War plans called for the initial landings on the Home Islands to be conducted approximately 90 days hence.  But, as we shall see, the invasion of Kyushu would actually have not been able to take place for anywhere from 120 to 135 days- a disastrous occurrence for the successful outcome of stated US war aims.

Some today assert, in effect, that it would have been more humane to have just continued the conventional B-29 bombing of Japan, which in six months had killed nearly 300,000 people and displaced or rendered homeless over 8 million more.  They also assert that the growing US blockade would have soon forced a surrender because the Japanese faced, quote: "imminent starvation." US Planners at the time, however, weren't nearly so bold, and the whole reason why advocates of tightening the noose around the Home Islands came up with so many different estimates of when blockade and bombardment might force Japan to surrender was because the situation wasn't nearly as cut and dried as it appears today, even when that nation's supply lines were severed.  Japan would indeed have become, quote:  "a nation without cities," as urban populations suffered grievously under the weight of Allied bombing; but over half the population during the war lived and worked on farms.  Back then the system of price supports that has encouraged Japanese farmers today to convert practically every square foot of their land to rice cultivation did not exist.  Large vegetable gardens were a standard feature of a family's land and wheat was also widely grown. 

The idea that the Japanese were about to run out of food any time soon was largely derived from repeated misreadings of the Summary Report of the 104-volume US Strategic Bombing Survey of Japan.  Using Survey findings, Craven and Cate, in the multi-volume US Army Air Force history of WWII detailed the successful US mine-laying efforts against Japanese shipping which essentially cut Japanese oil and food imports, and state only that by mid-August, quote: "the calorie count of the average man's fare had shrunk dangerously."  Obviously, some historians enthusiasm for the point they are trying to make has gotten the better of them since the reduced nutritional value of meals is somewhat different than "imminent starvation."

As for the Imperial Army itself, it was in somewhat better shape than is commonly understood today.  Moreover, the Japanese had figured us out. They had correctly deduced the landing beaches and even the approximate times of both invasion operations, and were thus presented with huge tactical and even strategic possibilities.  And although the Japanese had never perfected central control and massed fire of their artillery, this fact was largely irrelevant under such circumstances.   The months that the Japanese Sixteenth Army had to wait for the first US invasion, at Kyushu, were not going to be spent with its soldiers and the island's massive civilian population sitting on their duffs.  The ability to dig in and preregister, dig in and preregister, dig in and preregister, cannot be so casually dismissed.  To borrow a phrase from a recent Asian war, the Kyushu invasion areas were going to be a, quote: "target-rich environment" where artillery was going to methodically do its work on a large number of soldiers and Marines whose luck had run out.  On Okinawa, the US Tenth Army commander, General Buckner, was killed by artillery fire when the campaign was ostensibly in the mopping-up phase, and from World War I to the recent fighting in Grosny, where shells killed a Russian two-star general, there is ample evidence of artillery living up to its deadly reputation.

It has also been stated that US ground troops didn't really need to worry about Japanese cave defenses since combat experience in the Pacific, and tests run in the US, proved the effectiveness of self-propelled 8-inch and 155mm howitzer against caves and bunkers as well as their vulnerability to direct fire from tanks.  That the Japanese were also well aware of this and were arranging defensive positions accordingly from lessons learned on Okinawa and the Philippines is not mentioned.  In any event, the Japanese had already demonstrated that they could, with the right terrain, construct strongpoints, like Item Pocket on Okinawa, which could not be bypassed and had to be reduced without benefit of any direct-fire weapons since no tanks- let alone lumbering self-propelled guns- could work their way in for an appropriate shot.

Similarly, on the Japanese ability to defend against US tanks, Army and Marine armor veterans of the Pacific war would be amazed to learn that they had little to fear during the invasion.  After all, Japan's obsolescent 47mm anti-tank guns, quote:   "could penetrate the M-4 Sherman's armor only in vulnerable spots at very close range" and that their older 37mm gun was completely ineffective against the Sherman tank.  In fact, the Japanese, through hard experience, were becoming quite adept at tank killing.  During two actions in particular on Okinawa, they managed to knock out 22 and 30 Shermans respectively.  In one of these fights, Fujio Takeda managed to stop four tanks with six 400-yard shots from his supposedly worthless 47mm.   As for the 37mm, it was not intended to actually destroy tanks during the invasions but to immobilize them at very short ranges so that they would become easier prey for the infantry tank-killing teams that had proven so effective on Okinawa.

Some historians are also somewhat more confident than on-scene commanders as to our ability to pulverize Japanese defenses. This may be due, in part, to an overly literal interpretation of what the Japanese meant by "beach defenses," even though there is ample documentation on their efforts to develop positions well inland, out of range of the Navy's big guns.  One author, from the safe distance of five decades wrote:   "That coastal defense units could have survived the greatest pre-invasion bombardment in history to fight a tenacious, organized beach defense was highly doubtful."  I do believe something similar to this was confidently maintained just before the Somme in 1916, and it is worthwhile noting that every square inch of Iwo Jima and Okinawa was well within the range of the Navy's 8-, 12-, 14-, and 16-inch guns during those campaigns.  [Murmurs and whistle.]

Points like these may sound rather nit-picky but they assume great importance when you realize that, as noted earlier, the target date for Kyushu of 1 November 1945 was going to get pushed back as much as 45 days, giving the Japanese as much as four and a half months from the flashing red light of the 29 July intelligence estimate to prepare their defenses.

The Joint Chiefs originally set the date for the invasion of Kyushu (Operation Olympic) as X-Day, December 1, 1945, and for Honshu (Operation Coronet) as Y-Day, March 1, 1946.   To lessen casualties, the launch of Coronet would await the arrival of two armored divisions from Europe to sweep up Honshu's Kanto Plain and cut off Tokyo before the seasonal monsoons turned it into vast pools of rice, muck, and water crisscrossed by elevated roads and dominated by rugged, well-defended foothills.

Now, long before the British experienced the tragedy of pushing XXX Corps up a single road through the Dutch lowlands to Arnhem, an event popularized through the book and movie A Bridge too Far, US planners were well aware of the costs that would be incurred if the Kanto Plain was not secured for mobile warfare and airfield construction prior to the wet season. Intensive hydrological and weather studies begun in 1943 made it clear that an invasion in early March offered the best chance of success, with the situation becoming more risky as the month progressed.

With good luck, relatively free movement across the plain might even be possible well into April.  Unfortunately, this assumed that the snow run-off from the mountains would not be too severe, and that the Japanese would not flood the fields.   While subsequent post-war prisoner interrogations did not reveal any plans to systematically deluge low-lying areas, a quick thrust up the Kanto Plain would not have been as speedy as planners believed.  First, there were no bridges in the area capable of taking vehicles over 12 tons.  Every tank, every self-propelled gun, and prime mover would have to cross bridges erected for the event. Next, logistical considerations and the sequence of follow-up units would  require that armored divisions not even land until Y+10.  This would provide time for the defenders to observe that the US infantry's generic tank support was severely hampered by already flooded rice fields and- shall we say- suggest ways to make things worse for the invaders.

A late start on Honshu would leave American forces to fight their way up flood plains that were only dry during certain times of the year, but could be suddenly inundated by the Japanese.  If the timetable slipped for either operation, US soldiers and Marines on Honshu would risk fighting in terrain similar to that later encountered in Vietnam- minus the helicopters to fly over this mess- where all movement was readily visible from even low terrain features and vulnerable convoys moved on roads above rice paddies. Unfortunately, foul weather would have delayed base development on Kyushu and spelled a potentially disastrous late start for the operation on Honshu.

Planners envisioned the construction of 11 airfields on Kyushu for the massed airpower which would soften up Honshu.  Bomb and fuel storage, roads, wharves, and base facilities would be needed to support those air groups plus the US Sixth Army holding a 110-mile stop-line one third of the way up the island.  All plans centered on construction of the minimum essential operating facilities.  But that minimum grew.  The 31- that's 31 - air groups was increased to 40 then to 51 - all for an island
on which there was considerably less terrain information available than we erroneously believed we knew about Leyte.  Numerous airfields would come on line early to support ground operations on Kyushu, but the lengthy strips and support facilities for Honshu-bound medium and heavy bombers would only start to become available 45 days into the operation.  Most were not projected to be ready until 90 to 105 days after the initial landings on Kyushu in spite of a massive effort.

The constraints on the air campaign were so clear that when the Joint Chiefs set the target dates of the Kyushu and the Honshu invasions for December 1, 1945 and March 1, 1946, respectively, it was apparent that the three-month period between X-Day, Olympic and Y-Day, Coronet, would not be sufficient.  Weather ultimately determined which operation to reschedule
because Coronet could not be moved back without moving it closer to the monsoon season and thus risking serious restrictions on the ground campaign from flooded fields, and the air campaign from cloud cover that almost doubles from early March to early April.  This was a no-brainer.  MacArthur proposed bumping the Kyushu invasion ahead by a month.   As soon as this was pointed out, both Nimitz and the Joint Chiefs in Washington immediately agreed.  Olympic was moved forward one month to November 1, which also gave the Japanese less time to dig in.

Unfortunately these best-laid plans would not have unfolded as expected even if the atom bombs had not been dropped and the Soviet entry into the Pacific War had not frustrated Tokyo's last hope of reaching a settlement short of unconditional surrender- a Versailles-like outcome unacceptable to Truman and many of his contemporaries because it was seen as an incomplete victory that could well require the next generation to refight the war.  An infinitely bigger war than the late unpleasantness in Vietnam, which would have seen us sending troops overseas in 1965 to fight Japan instead of to Southeast Asia.  No deferments for that one.  [Laughter.]  The end result of this delay would have been an even more costly campaign on Honshu than was predicted.  A blood bath in which pre-invasion casualty estimates rapidly became meaningless because of something that the defenders could not achieve on their own, but a low pressure trough sitting along the Asian littoral would:  knock the delicate US timetable off balance.

The Divine Wind, or Kamikaze, of a powerful typhoon destroyed a foreign invasion force heading for Japan in 1281, and it was for this storm that Japanese suicide aircraft of World War II were named.  On October 9, 1945, a similar typhoon packing 140-mile per hour winds struck the American staging area on Okinawa that would have been expanded to capacity by that time if the war had not ended in September, and was still crammed with aircraft and assault shipping- much of which was destroyed.  US analysts at the scene matter-of-factly reported that the storm would have caused up to a 45-day delay in the   invasion of Kyushu.  The point that goes begging, however, is that while these reports from the Pacific were correct in themselves, they did not make note of the critical significance that such a delay, well past the initial- and unacceptable- target date of December 1, would have on base construction on Kyushu, and consequently mean for the Honshu invasion, which would have then been pushed back as far as mid-April 1946.

If there had been no atom bombs and Tokyo had attempted to hold out for an extended time- a possibility that even bombing and blockade advocates granted- the Japanese would have immediately appreciated the impact of the storm in the waters around Okinawa.   Moreover, they would know exactly what it meant for the follow-up invasion of Honshu, which they had predicted as accurately as the invasion of Kyushu.  Even with the storm delay and friction of combat on Kyushu, the Coronet schedule would have led US engineers to perform virtual miracles to make up for lost time and implement Y-Day as early in April as possible.  Unfortunately the Divine Winds packed a one-two punch.

On 4 April 1946, another typhoon raged in the Pacific, this one striking the northernmost Philippine island of Luzon on the following day where it inflicted only moderate damage before moving toward Taiwan.  Coming almost a year after the war, it was of no particular concern.  The Los Angeles Times gave it about a paragraph on the bottom of page 2.  But if Japan had held out, this storm would have had profound effects on the world we live in today.  It would have been the closest watched weather cell in history.  Would the storm move to the west after hitting Luzon, the Army's main staging area for Coronet, or would it take the normal spiraling turn to the north, and then northeast as the October typhoon?  Would slow, shallow-draft landing craft be caught at sea or in the Philippines where loading operations would be put on hold?  If they were already on their way to Japan, would they be able to reach Kyushu's sheltered bay?  And what about the breakwater caissons for the massive artificial harbor to be assembled near Tokyo?  The construction of the harbor's pre-fabricated components carried a priority second only to the atom bomb, and this precious towed cargo could not be allowed to fall victim to the storm and be scattered across the sea.   

Whatever stage of employment US forces were in during those first days of April, a delay of some sort- certainly no less than a week and perhaps much, much more- was going to occur.  A delay that the two US field armies invading Honshu, the First and Eighth, could ill afford and that Japanese militarists would see as yet another sign that they were right after all. This is critical.  Various authors have noted that much of the land today contains built-up areas not there in 1946, but are blissfully unaware that, thanks to the delays, anyone treading this same, quote: "flat, dry tank country" in 1946 would, in reality, have been up to their calves in muck and rice shoots by the time the invasion actually took place.

Recent years have also seen the claim that the kamikaze threat was overrated.  Time does not allow the subject to be discussed in any sort of detail here, but one aspect is worth emphasizing:  US intelligence turned out to be dead wrong about the number of Japanese planes available to defend the Home Islands.  Estimates that 6,700 could be made available in stages, grew to only 7,200 by the time of the surrender.  This number, however, turned out to be short by some 3,300 in light of the armada of 10,500 planes which the enemy planned to expend in stages during the opening phases of the invasion operations- most as Kamikazes.  All guesswork aside, occupation authorities after the war found that the number of military aircraft actually available in the Home Islands was over 12,700.  Another thing about those 3,300 undetected aircraft, it is worthwhile remembering that, excluding aircraft that returned to base, the Japanese actually expended well under half that number as Kamikazes at Okinawa, roughly 1,400, where over 5,000 US sailors were killed.

Of course, to some, all this discussion about the surprise 3,300 kamikaze aircraft, the delay of the Honshu landing until the rice paddies were flooded, etc., is all moot because the Japanese were supposedly just itching to surrender even before the dropping of the atom bombs and the Soviet Union's entry into the war.  Well, we'll just have to save that one for another time.  [NOTE:  For more on this side of the coin see Sadao Asada's article in the Fall 1998 Pacific Historical Review as well as the Herbert Bix piece in the Spring 1995 Diplomatic History.]  Thank you all for allowing me to address you today.  I'll conclude with a quick run-through of some slides to illustrate the tactical and strategic situation.

Slide 1-  Operation's Olympic and Coronet.  On the US side: 43 division equivalents.  At the time of the surrender, the divisions within the dashed lines were in various stages of transferring from French ports to the Philippines.  There were also approximately six more that were to be made available, three from Europe and three from the Pacific, with additional reserves in the continental United States.   Great Britain would have supplied a minimum of three more divisions.  Separate engineer, logistic and Army Air Force personnel would initially number in the hundreds of thousands and eventually surpass a million men.

Slide 2-  Close-up of the Olympic invasion area on Kyushu.  Divisions conducting initial assault.  Follow-on divisions.  Two Japanese corps.  No intent to take entire island with its multi-million civilian population. Advance to a stop line far enough from the developing anchorage and airbase construction to keep them out of artillery range.

Slide 3-  The provisional layout of the fighter defense of the Olympic invasion area.   Radar pickets.  Unlike Okinawa and the Marianas Turkey Shoot, where the great distances forced Japanese aircraft to approach along relatively narrow and predictable corridors, here the close proximity to bases would allow them to approach the highly vulnerable transports from anywhere along a wide arc.   Mountain passes.   The most dangerous scenario envisioned the Japanese slipping aircraft through the mountain passes and below the thin screen of combat air patrols- which, incidentally, is one of the things the Japanese planned to do.

Slide 4-  Coastal terrain typical of southern Kyushu.  This obviously would not be selected as a landing beach but even the ones selected had cliffs like these which were being heavily fortified.

Slide 5-  This is a Japanese illustration of one of the earlier coastal artillery positions built into the cliffs much like these at the British fortress at Gibraltar.   Later portals were left rough, both to conserve concrete and lessen their visibility.  Tunnels were also angled to give better protection from the direct fire of naval guns.

Slide 6-  Highly defensible terraced rice fields were a common feature on areas that could not be bypassed on both Kyushu and Honshu.

Slide 7-  The underground stockpiling of munitions, gasoline and other war supplies was well advanced at the time of the surrender, roughly four months before the opening invasion, and perhaps as much as eight long months before the assault on Honshu.   There is never enough time to prepare for an invasion, but from a purely technical standpoint, eight months is practically an eternity.  American planners worked from the assumption that the war could last into at least the end of 1946.  The Emperor was also not planning to go down fighting in the ruins of Tokyo as Hitler had in Berlin, and a massive staging area and underground complex beyond the Kanto Mountains was well on the way to completion when the war ended.  It was located about a hundred miles northwest of Tokyo near the Olympic site at Nagano.

Slide 8-  A Japanese poster warning the population that attacks on the Home Islands will intensify.  It reads:  Should there be air raids,  They will not be intended for destroying our Homeland, But will be aimed to strike at our morale,   Are we to let them destroy our Yamato fighting spirit?

Slide 9-  Japanese midget submarines at Kure naval base.  Reading the Summary Report of the huge US Strategic Bombing Survey one gets the impression that Japanese industry was kaput.  However, the highly political document was written to advance the objectives of air power advocates and presented a somewhat rosy picture of what the Army Air Force had accomplished.  As this photo demonstrates, not only could highly technical priority items still be produced in quantity, they could also be successfully hidden from the prying eyes of US reconnaissance aircraft fully six months after they commenced operations from nearby Okinawa.

Slide 10-  The operational plan for Operation Coronet called for a swift strike up the Kanto Plain to cut off Tokyo by a pair of US armored divisions from Europe.  As a practical matter, however, there was no way to actually conduct the envisioned movement in a timely fashion.  

Slide 11-  The brown area on these maps indicated areas of seasonal flooding in the plain.  Gray indicates areas that can be artificially flooded, while blue indicates land containing high densities of rice paddies.  Moreover, [back to slide 10] as US mechanized forces moved north along the highway between the low-lying areas and the foothills, more and more of their left
flank would be exposed to artillery in these foothills.  To get at this artillery, additional divisions would have to be pushed into the ever-lengthening hill mass to conduct fighting similar to that of Italy two years earlier and Korea five years in the future.  As of August 1945 this had not yet been anticipated, consequently no significant amount of troops had been allocated to this critical and manpower-intensive task.

Slide 12-  Even when rice paddies are ostensibly dry as this one is, they present formidable barriers to even tracked movement.  Moreover, the sodden nature of most dikes and paddy floors did not lend themselves to effective operation of devises like the hedgerow cutters in Normandy.  The rice paddies would have to be taken in a tedious, set-piece manner.
Meanwhile, the armored divisions fighting up the main road north past Tokyo would frequently find themselves limited to a one-tank front as happened to British XXX Corps when it was delayed reaching Arnhem by minimal German forces in the Dutch lowlands.

Slide 13-  Many are familiar with the various personal anti-tank weapons Japanese infantry were to employ, like hollow-charge rifle grenades plus the usually suicidal satchel charges and plethora of hand-operated hollow-charge mines.  However, the ///real/// killer of US tanks during the invasion- especially on the Kanto Plain- was going to be a weapon that the Japanese had been unable to put to good use so far in the war:  the Mark 97 20mm rapid-fire anti-tank rifle.  Even the comparatively thin frontal armor of the M4 Sherman was too thick for such a weapon, but in the paddy fields it was a different story.  At short range from expertly camouflaged positions, even a mediocre gunner could pump from two to a half dozen shots into the 1-inch and less belly armor of the Sherman as they reared up high over the dikes.  Passing beneath the driver and bow machine-gunner, the shells would smash into turret personnel, engine compartment and stored ammunition with catastrophic results.  Japanese divisions were initially issued only 18 of these weapons each.  After Saipan, the 20mm was manufactured in such great quantities that even the newest units contained the revised complement of 8 per rifle company- that's 72 per division.

Slide 14-  Last is a photo of the Sugar Loaf on Okinawa a relatively unimposing little hill with a total area of not much more than two football fields.  Note the size of the two soldiers at the summit.  Putting aside the artillery-studded foothills along the Eighth Army's steadily lengthening flank, and the ongoing slugfest along the elevated roads and rice paddies, it is useful to note  that there were many such unimposing terrain features on the Kanto Plain that, like this little Okinawan hill, could not be easily bypassed.  In five days of fighting in May 1945, the Japanese defenders here and on two supporting hills behind it inflicted over 3,000 Marine casualties- in spite of lavish tank and artillery support- before they were finally defeated.

Slide 15-  Two Down- One to Go.   [Cover of War Department pamphlet distributed to troops in summer 1945.]

Published by D. M. Giangreco on this subject from about 1995 to date:

"Casualty Projections for the U.S. Invasions of Japan: Planning and Policy
Implications" Journal of Military History (July 1997): 521-81

"To Bomb or Not to Bomb," Naval War College Review (Spring 1898): 140-45

"Truman and the Hiroshima Cult" and othe books reviewed, Naval History, US
Naval Institute (October 1995): 54-55

"Operation Downfall: US Plans and Japanese Countermeasures," at the
University of Kansas symposium Beyond Bushido: Recent Work in Japanese
Military History
, February 16, 1998

"Dropping the bomb on Japan: a-COUNT-ing for the Casualties" on the NET
television program Modern War, Washington, DC, December 12, 1997

"Operation Downfall:  The Devil Was In the Details," Joint Force Quarterly,
National Defense University (Autumn 1996): 86-94.

Chaired panel at the 1999 SMH conference at Penn State, What Did They Know
and When Did They Know It?:  Intelligence Assessments and Assumptions Before
the Invasion of Japan.  Papers available in booklet form in June:  Robert H.
Ferrell (Indiana State), Jacob W. Kipp (US Army Command and General Staff
College), General Makhmut Akhmetevich Gareev (Academy of Military Science,
Moscow) and Thomas B. Allen (National Geographic).

Letter, Journal of American History (June 1997): 322-23

Letter, Joint Force Quarterly (Summer 1996): 6-7

Letter, New England Quarterly (September 1998): 481-83.

Engaged in a general discussion of Robert P. Newman's work in the the
April 1998 American Historical Review, 663-64, and a book review
(Alperovitz et al) coming up in Parameters, US Army War College.  Subject
also comes up in newest book Dear Harry: The Truman Administration
through Correspondence with "Everyday Americans" (see  

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