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

by Daniel Wrinn

  Wada also had the 1st Independent Heavy Mortar Regiment firing the 320mm spigot mortars first encountered by Marines on Iwo Jima. Their ninety-six 81mm mortars were assigned for close infantry support and controlled by sector defense commanders.

  Potential infantry replacements varied from excellent with the 26th Shipping Engineer Regiment to meager at best with the various rear area service units. The 10th Air Sector Command provided 7,000 replacements composed of airfield maintenance and construction units at the Kadena and Yontan Airfields. Seven sea-raiding squadrons based at Kerama Retto had one-hundred handpicked men whose only assignment was to smash explosive-loaded suicide craft into the sides of cargo vessels and assault transports.

  A native Okinawan home guard (called Boeitai) rounded out the Thirty-second Army. These men were trained and integrated into Army units. The Boeitai gave Ushijima another 20,000 extra men to use as he pleased. Add to this 1,700 Okinawan children (thirteen years old and up) organized into volunteer youth groups called “Blood and Iron” for the Emperor’s duty units.

  US Army Troops

  The US Army played a significant role in the victory on Okinawa. The Army deployed as many combat troops, suffered comparable casualties, and fought with an equal heroism and bravery as the Marines.

  Army battles for Conical Hill, Kakazu Ridge, and the escarpment at Yuza Dake were just as bloody and memorable as Nishi Ridge and Sugar Loaf for the Marines. The Okinawa campaign still serves today as a model of joint service cooperation despite its isolated cases of sibling rivalry.

  In mid-1943, the Joint Chiefs identified three divisions in the Pacific with amphibious “proficiency.” The 1st and 2nd Marine Divisions were veterans of Tulagi and Guadalcanal, while the 7th Infantry was fresh from fighting in the Aleutians. These three units joined with four other divisions and constituted the Tenth Army bound for Okinawa. The number of divisions with experience in amphibious operations in the Pacific had now expanded sevenfold.

  Three assault units in General John Hodge’s XXIV Corps had recent experience with amphibious landings in the Battle for Leyte Gulf. It was the 96th Division’s first campaign and the third amphibious operation for the 7th Division after Kwajalein and Attu. The veteran 77th Division executed a daring landing at Ormoc, which surprised and slaughtered the enemy defenders.

  The 27th was a National Guard unit still bitterly regarded by Marines after their flail on Saipan, but still a proud unit with amphibious experience in the Marianas and Gilbert Islands. No other army divisions had the luxury of extended preparations for Okinawa. General MacArthur didn’t release the underfed and under-strength XXIV Corps (after 112 days of combat on Leyte) to the Tenth Army until seven weeks before L-Day on Okinawa. The 27th Division had more time but endured inadequate training in the jungles of Espiritu Santo.

  There were many examples of Marines and Army units cooperating in the Okinawan campaign. Army Air Force P-47 Thunderbolts flew long-range bombing and fighter missions for General Mulcahy’s Tactical Air Force. Army and Marine Corps units supported opposite services regularly during the long drive to the Shuri line. Marines gained a healthy respect for the Army’s 8-inch howitzers. These heavy weapons were often the only way to breach a well-fortified enemy strong point.

  General Buckner attached deadly “Zippo tanks” from the 713th Armored Flame Thrower Battalion along with 4.2-inch mortar batteries to both Marine divisions. The 6th Marine Division also had the 708th Amphibian Tank Battalion attached for the entire battle. Each of these units received a Presidential Unit Citation for service with their parent Marine units.

  The Army often gave logistical support to the Marines as the campaign slogged south during the endless rains. The Marines’ fourth revision of their table of organization still did not provide enough transfer assets to support such a lengthy campaign conducted far from the forces’ beachhead. A shortage of amphibious cargo ships assigned to the Marines also reduced the number of LVTs and wheeled logistics vehicles available. Often, the generosity of the supporting Army units determined if the Marines would eat that day.

  An example of this cooperative spirit happened on June 4, when soldiers from the 96th Division gave rations to Colonel Richard Ross’s starving and exhausted Marines. This brightened the battalion on a day otherwise known as “the most miserable day spent on Okinawa.”

  In short, Okinawa was too difficult and too large for one service to undertake. In this eighty-two-day campaign against a well-armed, resolute enemy, victory required teamwork and cooperation from several services.

  Marines Aviation Units

  According to Colonel Vernon McGee, landing force air support commander during the battle: “Okinawa was the culmination of the development of air support doctrine in the Pacific. The procedures we used there were results of all lessons learned in preceding campaigns—including the Philippines.”

  Marine aviation units on Okinawa operated across a range of missions: from bombing enemy battleships to supply drops. Over 700 Marine planes took part in the Okinawa campaign. An estimated 450 of these were engaged in combat for half the battle. Most Marine air units served under the Tenth Army’s TAF (Tactical Air Force) commanded by General Mulcahy. Outside of the TAF, Marine fighter squadrons were assigned to fleet carriers or escort carriers and long-range transports.

  Admiral Spruance commanded all Allied forces for Operation Iceberg. He believed the enemy’s air arm was the biggest threat to the mission’s success. Spruance made the Tenth Army’s first objective to secure the Kadena and Yontan Airfields and support land-based fighter squadrons.

  Assault forces achieve this on L-Day. The next day, General Mulcahy moved his command post ashore and began TAF operations. His top priority was to maintain air superiority over Okinawa and the Fifth Fleet. Because of the massed kamikaze attacks unleashed by the Japanese, this mission kept Mulcahy preoccupied for many weeks.

  Army and Marine aviation units composed Mulcahy’s Tactical Air Force. His force had fifteen Marine fighter squadrons, ten Army fighter squadrons, two Marine torpedo bomber squadrons, and sixteen Army bomber squadrons. Marine fighter pilots flew F4U Corsairs and radar-equipped, night-fighting F6F Hellcats. Army pilots flew P-47 Thunderbolts, and their night fighters were P-61 Black Widows.

  Allied pilots fought air-to-air duels against kamikazes and plenty of other late-model “Franks” and “Jacks.” Altogether, the Tactical Air Force pilots shot down 627 planes. Colonel Ward Dickey’s Marine Aircraft Group (MAG-33) set the record with 215 kills—more than half claimed by the “Death Rattlers”—Major George Axtell’s squadron VMF-323.

  The need to protect the Fleet caused some ground commanders to worry that their own close-in air support would be “short-sheeted.” But escort carrier Naval squadrons picked up the slack. They flew over sixty percent of the close-in support missions between April 1 and the end of June. The combined TAF and carrier pilots flew over 14,000 air support sorties. Over 5,000 of these supported Marines on the ground. Pilots dropped over 150,000 gallons of napalm on enemy positions.

  Air Liaison Parties accompanied the frontline divisions and directed aircraft to the target. Coordinating these lower echelon requests became the responsibility of three Marine Landing Force Air Support Control Units. One represented the Tenth Army to the fleet while the others were responsive to IIIAC and the XXIV Corps. This technique refined experiments McGee had started on Iwo Jima. In most cases, close air support for the infantry was extremely effective. Several units reported safe and prompt delivery of ordnance on target within 150 yards. But there were also accidents and delays (less than a dozen) and situations where lines were simply too intermingled for any air support.

  Other Marine aviation units helped in the victory on Okinawa. Marine torpedo bomber pilots flew their Avenger “torpeckers” in zero-zero weather. They dropped over 40,000 pounds of medical supplies, rations, and ammunition to forward-deployed ground units. The fragile and small Grasshoppers of the Marine Observation Squadrons flew 3,487 missions of
artillery spotting, medical evacuations, and photo-reconnaissance. One artillery officer described the Grasshopper pilots as: “the unsung heroes of Marine aviation. They’d often fly past cave openings and look in to see if the Japs were hiding a gun in there.”

  Marine pilots served on Okinawa with panache. During a desperate dogfight, one pilot radioed: “Come on up here and help me. I got two Franks, and a Zeke cornered.” Those were his last words, but his fighting spirit persisted. According to a destroyer skipper who’d just been rescued from swarms of kamikazes by Marine Corsairs: “I’d take my ship to the shores of Japan if I could have those Marines with me.”

  Artillery on Okinawa

  Because of the tactics selected and the nature of enemy defenses, Okinawa was the most significant battle in the war for artillery units. General Geiger landed with fourteen firing battalions with the IIIAC. And when the 2/10 Marines came ashore to support the 8th Marines—the total rose to fifteen firing battalions.

  General David Nimmer commanded the III Corps Artillery with three batteries of 155mm howitzers and three 155mm “Long Tom” guns. The Marines had considerably enhanced their firepower since the initial Pacific campaigns.

  While one 75mm howitzer battalion still remained, the 105mm howitzer had become the norm for division artillery. Infantry units on the front line were supported by the 75mm fire of medium tanks and LVT-As. New self-propelled “siege guns” with 4.5-inch multiple rocket launchers fired by the “Buck Rogers” men and attached Army 4.2 mortar platoons caused chaos on Japanese positions.

  Colonel Fred Henderson described this devastating array of fire support: “Not many people realize that the Tenth Army’s artillery, plus the LVT-As and naval gunfire gave us a guns/mile of front ratio on Okinawa that was higher than any US effort in all of World War II.”

  General Buckner tasked his commanders to integrate field artillery support early in the campaign. General Geiger sent his corps artillery and 11th Marines (not fully committed in the opening weeks) to help the XXIV Army Corps in their early assaults against the outer Shuri defenses. From April 7 to May 6, these artillery units fired over 55,000 rounds in support of the XXIV Corps. But this was only the beginning. Once both IIIAC Marine divisions entered the lines, they benefited from Army artillery support and organic fire support—two Marine and two Army.

  By the end, the Tenth Army artillery rockets had fired over two million rounds downrange. In addition, 707,000 mortars, rockets, and five-inch or larger shells were fired from naval gunfire ships offshore. Half of the artillery rounds were from 105mm howitzer shells and the M-7 self-propelled guns. Compared to these bigger guns, the older 75mm pack howitzers were the battlefield’s “Tiny Tims.” Their versatility and mobility proved valuable through the long haul. According to Colonel Brown, who commanded the LVT-As firing similar ammunition: “The 75mm was plentiful and contrasted with the heavy calibers, so we used it for fire interdiction and harassing missions across the front.”

  Generals del Valle and Geiger expressed interest in the army’s larger weapons. Geiger respected the Army’s 8-inch howitzer 200-pound shell. It had much more penetrating and destroying power than the 155mm gun’s ninety-five-pound shell—largest in the Marine’s inventory. Geiger urged Marine Corps Headquarters to form 8-inch howitzer battalions for the next attack on Japan. Geiger also praised the accuracy, range, and power of the Army’s 4.2-inch mortars, and recommended their inclusion in the Marine division.

  On several occasions, artillery commanders were tempted to orchestrate all this killing power into one mighty concentrated attack. Time on target (TOT) missions frequently occurred in the early weeks, but their high consumption rates were a drawback. Late in the campaign, Colonel Brown coordinated a massive TOT with twenty-two battalions against enemy positions in southern Okinawa. This sudden concentration worked brilliantly, but Brown failed to inform the generals and woke everyone from a sound sleep. Brown “caught hell” from all sides.

  Geiger insisted the LVT-As were also trained as field artillery. While this was done, the opportunity for direct fire support in the assault waves fizzled on L-Day when the enemy chose to not defend the Hagushi breaches. Colonel Lewis Metzger’s 1st Armored Amphibian Battalion LVT-As fired over 20,000 rounds of 75mm shells in an artillery support role after L-Day.

  Marines made great advances in refining supporting arms coordination during the battle for Okinawa. Commanders established Target Information Centers (TIC) at every level from battalion up to Tenth Army. The TICs provided centralized target information and a weapons assignment system responsive to both assigned targets and targets of opportunity. All three component liaison officers: air, artillery, and naval gunfire, were staffed with target intelligence information officers.

  This commitment to innovation led to significant support improvements for the foot-slogging infantry. As one rifle battalion commander later wrote: “It wasn’t uncommon for a battleship, artillery, tanks, and aircraft to be supporting the efforts of a single platoon during the assault on Shuri.”

  Sherman M-4 Tanks

  Seven Marine and Army tank battalions were deployed on Okinawa. They were a deadly weapon—but only when coordinated with accompanying infantry. The Japanese tried to separate the two components by boldness and fire.

  Before the invasion, General Ushijima said: “The strength of the enemy’s forces is with his tanks.” Ushijima’s anti-tank training received the highest priority within his Thirty-second Army. These preparations proved successful on April 19, when the Japanese knocked out twenty-two out of the thirty Sherman tanks of the 27th Division—mostly by suicidal demolitionists.

  The Marines fared better. They learned in earlier campaigns how to integrate artillery and infantry in a close protective over-watch of their tanks and to keep the “human bullet” suicide squads at bay. While enemy mines and guns took their toll on the Shermans, only one Marine tank sustained damage from a Japanese suicide attack.

  Colonel Arthur Stewart commanded the 1st Tank Battalion on Okinawa. His unit had fought with distinction at Peleliu six months earlier, despite shipping shortfalls that kept a third of his tanks out of the fight. Stewart insisted on keeping the battalion’s older M-4A2 Shermans because their twin (General Motors) diesel engines were safer in combat: “The tanks were not so easily set on fire and blown up under enemy fire,” Stewart wrote after the war.

  Colonel Rob Denig preferred the newer Sherman model M-4A3 for his 6th Tank Battalion. Denig’s tank crews liked the greater horsepower provided by the water-cooled Ford V-8 engines. They considered the reversion to gasoline from diesel an acceptable risk. The 6th Tank Battalion faced its greatest challenge against Admiral Ota’s naval guns and mines on the Oroku Peninsula.

  Sherman tanks were harshly criticized in the European theater for coming up short against the heavier German Tiger Tanks. But they were ideal for island fighting in the Pacific. On Okinawa, the Sherman's limitations were obvious. Their 75mm gun was too light against most of Ushijima’s fortifications. But the new M-7 self-propelled 155mm gun worked well. Shermans were never known for their armor protection. At thirty-three tons, their strength was more in mobility and reliability. Japanese anti-tank weapons and mines reached the height of their deadliness on Okinawa. The Sherman’s thin-skinned weak points (1.5-inch armor on the rear and sides) caused considerable concern.

  Marine tank crews sheathed the sides of their tanks with lumber to thwart hand-lobbed Japanese magnetic mines as early as the Marshalls. By Okinawa, the Shermans were draped with spot-welded track blocks, sandbags, wire mesh, and clusters of large nails—designed to enhance armor protection.

  Both tank battalions had their Shermans configured with dozer blades (valuable for cave fighting), but neither deployed with flame tanks. Despite the rave reports of the USN Mark I turret-mounted flame system installed on the Shermans in the Iwo Jima battle, there was no retrofit program for the Okinawa-bound Marine tank units. All flame tanks on Okinawa were provided courtesy of the US Army’s 713th
Armored Flamethrower Battalion. Company B of that unit supported the Marines with three brand-new H1 flame tanks. Each carried 290 gallons of napalm thickened fuel—good for two-and-a-half minutes of flame at a range of 200 yards.

  Marines used the new T-6 “tank flotation devices” to get the initial waves of Shermans ashore on L-Day. The T-6 was a series of floating tanks welded around the hull. They had a provisional steering device that made use of the tracks and electric bilge pumps. Once ashore, the crew jettisoned the bulky rig with built-in explosive charges.

  The April 1 landing for the 1st Tank Battalion was truly “April Fool’s Day.” An LST (Landing Ship Tank) captain carrying six Shermans equipped with a T-6 launched the vehicles an hour late and eleven miles out to sea. It took them five hours to reach the beach (losing two tanks on the reef at ebb tide). Most of Colonel Stewart’s other Shermans made it ashore before noon, but some of his reserves could not make it across the reef for another forty-eight hours.

  The Sixth Tank Battalion had better luck. Their LST skippers launched their T-6 tanks on time and close in. Two tanks were lost: one sank after its main engine failed, and the other broke a track and swerved into a hole. The other Shermans surged ashore and were ready to roll.

  Enemy gunners and mine warfare experts knocked out three Marine Shermans in the battle. Many more tanks took damage from the fighting but were repaired by the hard-working maintenance crews. Because of their ingenuity, the assault infantry battalions never lacked armored firepower, shock action, and mobility.

  Amphibious Reconnaissance

  A series of smaller amphibious operations around the periphery of Okinawa helped contribute to victory. These landing forces varied in size from the company level to an entire division. Each reflected the apex of amphibious expertise learned in the Pacific theater by 1945. These landings produced fleet anchorages, auxiliary airfields, fire support bases, and expeditionary radar sites, giving an early warning to the fleet against the dreaded kamikazes.