Operation Iceberg: 1945 Victory on Okinawa (WW2 Pacific Military History Series) Read online

  Operation Iceberg

  1945 Victory on Okinawa

  Daniel Wrinn

  Contents

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  Seizing Shuri Castle

  Operation Iceberg

  Japanese Defenses

  Land the Landing Force

  Battle of Yae Take

  Typhoon of Steel

  Situation at Sea

  Blowtorch and Corkscrew

  Sugar Loaf Hill

  Day and Bertoli

  Screaming Mimi

  Wrapping up the Fight

  Senior Commanders

  Blood and Iron

  US Army Troops

  Marines Aviation Units

  Artillery on Okinawa

  Sherman M-4 Tanks

  Amphibious Reconnaissance

  Legacy of Okinawa

  Also By Daniel Wrinn

  References

  About the Author

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  Seizing Shuri Castle

  At dawn on May 29, 1945, the 1st Marine Division began their fifth consecutive week of frontal assaults. This was part of the Tenth Army’s relentless offensive against Japanese defenses in southern Okinawa.

  Operation Iceberg’s mission to secure Okinawa was now two months old and badly bogged down. The fast-paced opening had been replaced by weeks of exhausting and bloody attrition warfare against the Shuri Castle.

  The 1st Division were hemmed in between two other divisions. They had precious little room to maneuver and had advanced less than a thousand yards in eighteen days. An average of fifty-five murderous yards per day. Their sector was one bristling, honeycombed ridgeline after another—Kakazu, Dakeshi, and Wana.

  But just beyond was the long shoulder of Shuri Ridge. Nerve center of the Imperial Japanese Thirty-second Army. The outpost of dozens of forward artillery observers, who’d made life miserable for the Allied landing force. On this wet, rainy, and cold morning, things were different. It was quieter. After days of savage and bitter fighting, Allied forces overran Conical Hill to the east and Sugar Loaf to the west. Shuri Castle no longer seemed invincible.

  The 1/5 Marines moved out cautiously and expected the usual firestorm of enemy artillery at any moment. But there was none. Marines reached the crest of Shuri Ridge without a fight. Amazed, the company commander looked west along the road toward the ruins of Shuri Castle: a medieval fortress of ancient Ryukyuan kings.

  Soldiers in the Tenth Army expected the Japanese to defend Shuri to the death, but the place seemed lightly held. Spiteful small arms fire came from nothing more than a rearguard. Field radios buzzed with this surprising news. Shuri Castle laid in the distance, ready for the taking. Marines asked for permission to seize their long-awaited prize.

  General Pedro del Valle, CO of the 1st Marine Division, didn’t hesitate. According to corps division boundaries, Shuri Castle belonged to soldiers of the 77th Infantry Division. General del Valle knew his counterpart, Army General Andrew Bruce, would be furious if the Marines snatched their long-sought trophy before his soldiers could arrive. This was a unique opportunity to grab the Tenth Army’s primary objective. General del Valle gave the go-ahead, and with that, the 1/5 Marines raced along the west ridge against light opposition and secured Shuri Castle.

  After General del Valle’s staff did some fancy footwork to keep peace with their army neighbors, they learned the 77th had scheduled a massive castle bombardment that morning. Frantic radio calls averted the near-catastrophe just in time. General Bruce was infuriated by the Marines’ unauthorized initiative. Del Valle later wrote: “I don’t think a single Army commander would talk to me after that.”

  Through the inter-service aggravation, Allied forces had achieved much this morning. For two months, Shuri Castle had provided the Japanese with a superb field of observed fire—covering southern Okinawa's entire five-mile neck. But as the 1/5 Marines deployed into a defensive line within the castle’s rubble, they were unaware that a Japanese rearguard still occupied a massive subterranean headquarters underneath them. Marines soon discovered that directly under their muddy boondockers was the underground headquarters of the Japanese Thirty-second Army. This mammoth complex was over 1,200 feet long and 160 feet deep: all dug by pick and shovel.

  The enemy had stolen a march on the approaching Tenth Army. Japanese forces retreated south during the rains and occupied the third (final) ring of their prepared underground defenses: a series of fortified escarpments on the Kiyamu Peninsula.

  Seizing Shuri Castle was an indisputable milestone in the Okinawa campaign. Still, it was a hollow victory. Like the flag-raising on Iwo Jima’s Suribachi signified the end of the beginning of that prolonged battle. The capture of Shuri Castle did not end the fighting. The savage slugfest on Okinawa continued for another twenty-four days—while the plum rains fell and the horrors and dying on both sides continued.

  Operation Iceberg

  The battle of Okinawa covered a seven-hundred-mile arc from Kyushu to Formosa. It involved a million combatants—Japanese, Americans, British, and Okinawan natives. This battle rivaled the Normandy invasion because it was the biggest and bloodiest operation of the Pacific War. In eighty-two days of combat, Allied forces and unfortunate noncombatants suffered an average of 3,000 lives lost a day.

  By the spring of 1945, the Empire of Japan was a wounded wild animal: desperate, cornered, and furious. Japanese leaders knew Okinawa under Allied control would be transformed into “the England of the Pacific.” It would serve as a staging point for the invasion of the sacred homeland. The Japanese would sacrifice everything to avoid the unspeakable disgrace of unconditional surrender and foreign occupation.

  The US Navy was presented with its greatest operational challenge to date: how to protect a gigantic and exposed amphibious task force tethered to the beachhead against Japanese kamikaze attacks. Okinawa would be the ultimate test of US amphibious power and projection. Could Allied forces in the Pacific Theater plan and execute such a massive assault against a heavily defended landmass? Could the Allies integrate the tactical capabilities of all the services and fend off every imaginable form of counterattack while maintaining operational momentum?

  Operation Iceberg was not executed in a vacuum. Preparatory action to the invasion kicked off at the same time campaigns on Iwo Jima and the Philippines were still being wrapped up—another strain on Allied resources. But as dramatic and sprawling as the battle of Okinawa proved to be, both sides saw this contest as an example of the even more desperate fighting soon to come with the invasion of the Japanese home islands. The closeness of Okinawa to Japan was well within medium bomber and fighter escort range. Its valuable military ports, anchorages, airfields, and training areas made this skinny island imperative for Allied forces—eclipsing their earlier plans for the seizure of Formosa.

  Okinawa is the largest of the Ryukyuan Islands. The island sits at the apex of a triangle nearly equidistant to strategic areas. Formosa is 330 miles to the southwest, Kyushu is 350 miles to the north, while Shanghai is 450 miles to the west. As on so many Pacific battlefields, Okinawa had a peaceful heritage. Officially an administrative prefecture of Japan (forcibly seized in 1879), Okinawans were proud of their long Chinese legacy and unique sense of communit
y.

  Imperial headquarters in Tokyo did little to garrison or fortify Okinawa at the beginning of the Pacific War. After the Allies conquered Saipan, Japanese headquarters sent reinforcements and fortification materials to critical areas within the “Inner Strategic Zone,” Peleliu, the Philippines, Iwo Jima, and Okinawa.

  Imperial Japanese headquarters on Okinawa formed a new field army: the Thirty-second Army. They funneled different trained components from Japan’s armed perimeter in China, Manchuria, and the home islands. American submarines took a deadly toll on these Japanese troop movements. On June 29, 1944, the USS Sturgeon torpedoed the transport Toyama Maru. She sank with a loss of 5,600 troops of the 44th Independent Mixed Brigade en route for Okinawa. It would take the Japanese the rest of the year to replace that loss.

  In October 1944, US Joint Chiefs decided to act on the strategic value of the Ryukyus. They tasked Admiral Nimitz with seizing Okinawa after the Iwo Jima campaign. The Joint Chiefs ordered Nimitz to seize, occupy, and defend Okinawa before transforming the captured island into an advanced staging base for the invasion of Japan.

  Nimitz turned to his most veteran commanders to execute this mission. Admiral Spruance, the victor of Midway and the Battle of the Philippine Sea, would command the US Fifth Fleet (debatably the most powerful armada of warships ever assembled). Admiral Kelly Turner, veteran of the Solomons and Central Pacific landings, would command all amphibious forces under Spruance. But Kelly Turner’s military counterpart would no longer be the old warhorse General Holland Smith. Iwo Jima was Smith’s last fight. Now the expeditionary forces had grown to the size of a field army with 182,000 assault troops. Army General Simon Buckner (son of the Confederate general who fought against Grant at Fort Donaldson in the American Civil War) would command the newly formed US Tenth Army.

  General Buckner made sure the Tenth Army reflected his multi-service composition. Thirty-four Marine officers served on Buckner’s staff, including General Oliver P. Smith as his deputy Chief of Staff. Smith later wrote: “the Tenth Army became, in effect, a joint task force.”

  Six veteran divisions, two Marine and four Army, composed Buckner’s landing force. A division from each service was marked for reserve duty—another sign of the growth of Allied amphibious power in the Pacific. Earlier in the war, Americans had landed one infantry division on Guadalcanal, two in the Palaus, and three each on Iwo Jima and Saipan. But by spring 1945, Buckner and Spruance could count on eight experienced divisions besides those still on Luzon and Iwo Jima.

  The Tenth Army had three major operational components. Army General John Hodge commanded the XXIV Corps, composed of the 77th and 96th Infantry Divisions (with the 27th Infantry Division in floating reserve and the 81st Infantry Division in area reserve). Marine General Roy Geiger commanded the III Amphibious Corps, composed of the 1st and 6th Marine Divisions (with the 2nd Marine Division held in floating reserve). Marine General Francis Mulcahy commanded the Tenth Army’s Tactical Air Force and the 2nd Marine Aircraft Wing.

  The Marine components for Operation Iceberg were scattered. The 1st Marines had returned from Peleliu to “Pitiful Pavuvu” in the Russell Islands to prepare for the next fight. The 1st Marine Division had been the first to deploy into the Pacific. They executed brutal amphibious campaigns on Guadalcanal, Cape Gloucester, and Peleliu. Over one-third of the 1st Marines were veterans of two of those battles.

  Pavuvu’s tiny island limited work-up training, but a large-scale exercise on neighboring Guadalcanal enabled the division to integrate its replacements and returning veterans. General del Valle drilled his Marines in tank-infantry training under the protective umbrella of supporting howitzer fire.

  The 6th Marine Division was the only division formed overseas in the war. General Lemuel Shepherd activated the colors and assumed command on September 12, 1944. While this unit was newly formed, it was not green—several former Marine Raiders with combat experience comprised the heart of this Marine division. General Shepherd used his time and the more extensive facilities on Guadalcanal to conduct work-up training from the platoon to the regimental level. He looked ahead to Okinawa and emphasized rapid troop deployments and large-scale operations in built-up combat areas.

  General LeRoy Hunt commanded the 2nd Marine Division. Hunt’s Marines had returned to Saipan after the conquest of Tinian. The division had absorbed 8,000 replacements and trained for a wide-ranging series of mission assignments as a strategic reserve. The 2nd Division possessed a vital lineage in the Pacific War at Guadalcanal, Tarawa, Saipan, and Tinian. Its presence in the Ryukyus’ waters would establish a fearsome “amphibious force-in-being” to distract the Japanese on Okinawa. This division would pay an unequal price for its bridesmaid role in the coming campaign.

  The Marine assault force preparing for Okinawa was dealt another organizational change—the fourth of the war. Marine headquarters constantly reviewed “lessons learned” in the war and had just completed a series of revisions to the table of organization for its divisions and components. While it would not become official until a month after the landing, the divisions had already made most changes.

  The overall size of each division increased to 19,176 (from 17,465). This was done by adding an assault signal company, a rocket platoon (Buck Rogers Men), a fifty-five man assault platoon in each regimental headquarters, and a war dog platoon. Motor transport, artillery, and service units also received slight increases, as did machine-gun platoons in each rifle company. But the most timely weapons change happened by replacing the 75mm half-tracks with the new M-7s (105mm self-propelled howitzer). Artillery regiment purists did not approve of these weapons being deployed by the infantry. These M-7s would not be used as massed howitzers but as direct fire “siege guns” against the thousands of fortified caves on Okinawa.

  Marine Corps Headquarters backed up these last-minute changes by providing the required replacements to land the assault divisions at full strength. Sometimes the skills required did not match. Some artillery regiments absorbed a flood of radar technicians and anti-aircraft artillery gunners from old defense battalions. But the manpower and equipment shortfalls that had plagued earlier operations were overcome by the time the assault force embarked on Operation Iceberg.

  Even this late in the war, operational intelligence was unsatisfactory before the landing. At Tarawa and Tinian, the pre-assault combat intelligence had been brilliant. But at Okinawa, the landing force did not have accurate figures of the enemy's weapons or abilities.

  The cloud cover over the island prevented accurate and complete photo-reconnaissance. Also, the ingenuity of the Japanese commander and the extraordinary digging skills of the enemy garrison helped disguise the island's true defenses.

  Japanese Defenses

  Okinawa is sixty miles long, but only the lower third of the island had the military objectives of anchorages, ports, and airfields. In August 1944. Japanese General Mitsuru Ushijima took command of the Thirty-second Army. He understood the fight would be fought in the south and concentrated his forces there.

  He decided to not challenge the probable Allied landings in Hagushi along the broad beaches of the southwest coast. He believed that doing so would lose him the Kadena and Yontan airfields. This decision allowed him to conserve his forces and fight the only battle that stood a chance: an in-depth defense, underground and protected from the overpowering Allied air and arms superiority.

  This clash of cave warfare and attrition would be like the recent battles on Peleliu and Iwo Jima. Each had taken a terrifying cost to Allied invaders. General Ushijima sought to replicate this strategy. He would go underground and sting the Allies with high caliber gunfire from his freshly excavated fire-port caves. He believed by bleeding the landing force and bogging down their momentum, he could buy the Imperial Army and Navy’s air arms enough time to destroy the fifth fleet with massed kamikaze attacks.

  General Ushijima had 100,000 Imperial troops on the island, including thousands of Okinawan Home Guard (conscripts known as
Boeitai). He had a disproportionate number of heavy weapons and artillery in his command. The Allies in the Pacific would not encounter a more formidable concentration of 47mm antitank guns, 320mm spigot mortars, 120mm mortars, and 150mm howitzers. The strategic decision to invade Peleliu, Iwo Jima, and the Philippines before Okinawa gave the enemy seven months to develop their defenses.

  Allied forces had already seen what the Japanese could do to fortify a position in a short time. On Okinawa they achieved stunning success. They worked almost exclusively with hand tools: not one bulldozer on the entire island. The Japanese dug miles of underground fighting positions and honeycombed southern Okinawa’s ridges and draws. They stocked each position with reserves of food, water, ammunition, and medical supplies. Allied forces anticipated a fierce defense of the southwestern beaches and the airfields, followed by a general counterattack. Then, the battle would be over except for some mop-up and light patrolling.

  The Allies could not have been more mistaken.

  The assault plan called for the advance seizure of the Kerama Retto Islands after several days of preparatory air and naval bombardment. Followed by a massive four-division assault on the Hagushi Beaches. During the primary assault, the 2nd Marine Division, with a separate naval task force, would duplicate the assault on Okinawa’s southeast coast (Minatoga Beaches).

  Love-Day (chosen to avoid planning confusion with D-Day being planned for Iwo Jima) would happen on April 1, 1945. Hardly anyone failed to remark about the irony of April Fool’s Day and Easter Sunday.