Island Hopping in World War II: A Path to Victory in the Pacific

Advancing Across the Pacific

Battle of Tarawa
Marines storm Tarawa, Gilbert Islands, November 1943. (National Archives & Records Administration)

In mid-1943, the Allied command in the Pacific began Operation Cartwheel, which was designed to isolate the Japanese base at Rabaul on New Britain. The key elements of Cartwheel involved Allied forces under General Douglas MacArthur pushing across northeastern New Guinea, while naval forces secured the Solomon Islands to the east. Rather than engage sizable Japanese garrisons, these operations were designed to cut them off and let them "whither on the vine." This approach of bypassing Japanese strong points, such as Truk, was applied on a large scale as the Allies devised their strategy for moving across the central Pacific.

Known as "island hopping," U.S. forces moved from island to island, using each as a base for capturing the next. As the island hopping campaign began, MacArthur continued his push in New Guinea while other Allied troops were engaged in clearing the Japanese from the Aleutians.

Tarawa

The initial move of the island hopping campaign came in the Gilbert Islands when U.S. forces struck Tarawa Atoll. The capture of the island was necessary as it would allow the Allies to move on to the Marshall Islands and then the Marianas. Understanding its importance, Admiral Keiji Shibazaki, Tarawa's commander, and his 4,800-men garrison heavily fortified the island. On November 20, 1943, Allied warships opened fire on Tarawa and carrier aircraft began striking targets across the atoll. Around 9:00 a.m., the 2nd Marine Division began coming ashore. Their landings were hampered by a reef 500 yards offshore that prevented many landing craft from reaching the beach.

After overcoming these difficulties, the Marines were able to push inland, though the advance was slow. Around noon, the Marines were finally able to penetrate the first line of Japanese defenses with the assistance of several tanks that had come ashore. Over the next three days, US forces succeeded in taking the island after brutal fighting and fanatical resistance from the Japanese.

In the battle, U.S. forces lost 1,001 killed and 2,296 wounded. Of the Japanese garrison, only seventeen Japanese soldiers remained alive at the end of the fighting along with 129 Korean laborers.

Kwajalein & Eniwetok

Using the lessons learned at Tarawa, U.S. forces advanced into the Marshall Islands. The first target in the chain was Kwajalein. Beginning on January 31, 1944, the islands of the atoll were pummeled by naval and aerial bombardments. Additionally, efforts were made to secure adjacent small islands for use as artillery fire bases to support the main Allied effort. These were followed by landings carried out by the 4th Marine Division and the 7th Infantry Division. These attacks easily overran the Japanese defenses and the atoll was secured by February 3. As at Tarawa, the Japanese garrison fought to nearly the last man, with only 105 of nearly 8,000 defenders surviving.

As US amphibious forces sailed northwest to attack Eniwetok, the American aircraft carriers were moving to strike the Japanese anchorage at Truk Atoll. A principal Japanese base, US planes struck the airfields and ships at Truk on February 17-18, sinking three light cruisers, six destroyers, over twenty-five merchantmen, and destroying 270 aircraft.

As Truk was burning, Allied troops began landing at Eniwetok. Focusing on three of the atoll's islands, the effort saw the Japanese mount a tenacious resistance and utilize a variety of concealed positions. Despite this, the islands of the atoll were captured on February 23 after a brief but sharp battle. With the Gilberts and Marshalls secure, U.S. commanders began planning for the invasion of the Marianas.

Saipan & the Battle of the Philippine Sea

Comprised primarily of the islands of Saipan, Guam, and Tinian, the Marianas were coveted by the Allies as airfields that would place the home islands of Japan within range of bombers such as the B-29 Superfortress. At 7:00 a.m. on June 15, 1944, U.S. forces led by Marine Lieutenant General Holland Smith's V Amphibious Corps began landing on Saipan after a heavy naval bombardment.

The naval component of the invasion force was overseen by Vice Admiral Richmond Kelly Turner. To cover Turner and Smith's forces, Admiral Chester W. Nimitz, Commander-in-Chief of the US Pacific Fleet, dispatched Admiral Raymond Spruance's 5th US Fleet along with the carriers of Vice Admiral Marc Mitscher's Task Force 58. Fighting their way ashore, Smith's men met determined resistance from 31,000 defenders commanded by Lieutenant General Yoshitsugu Saito.

Understanding the importance of the islands, Admiral Soemu Toyoda, commander of the Japanese Combined Fleet, dispatched Vice Admiral Jisaburo Ozawa to the area with five carriers to engage the U.S. fleet. The result of Ozawa's arrival was the Battle of the Philippine Sea, which pitted his fleet against seven American carriers led by Spruance and Mitscher. Fought June 19-20, American aircraft sank the carrier Hiyo, while the submarines USS Albacore and USS Cavalla sank the carriers Taiho and Shokaku. In the air, American aircraft downed over 600 Japanese aircraft while only losing 123 of their own. The aerial battle proved so one-sided that US pilots referred to it as "The Great Marianas Turkey Shoot." With only two carriers and 35 aircraft remaining, Ozawa retreated west, leaving the Americans in firm control of the skies and waters around the Marianas.

On Saipan, the Japanese fought tenaciously and slowly retreated into the island's mountains and caves. U.S. troops gradually forced the Japanese out by employing a mix of flamethrowers and explosives.

As the Americans advanced, the island's civilians, who had been convinced that the Allies were barbarians, began a mass suicide, jumping from the island's cliffs. Lacking supplies, Saito organized a final banzai attack for July 7. Beginning at dawn, it lasted over fifteen hours and overran two American battalions before it was contained and defeated. Two days later, Saipan was declared secure. The battle was the costliest to date for American forces with 14,111 casualties. Almost the entire Japanese garrison of 31,000 was killed, including Saito, who took his own life. 

Guam & Tinian

With Saipan taken, U.S. forces moved down the chain, coming ashore on Guam on July 21. Landing with 36,000 men, the 3rd Marine Division and 77th Infantry Division drove the 18,500 Japanese defenders north until the island was secured on August 8. As on Saipan, the Japanese largely fought to the death and only 485 prisoners were taken. As fighting was occurring on Guam, American troops landed on Tinian. Coming ashore on July 24, the 2nd and 4th Marine Divisions took the island after six days of combat. Though the island was declared secure, several hundred Japanese held out in the Tinian's jungles for months. With the Marianas taken, construction began on massive airbases from which raids against Japan would be launched.

Competing Strategies & Peleliu

With the Marianas secured, competing strategies for moving forward arose from the two principal U.S. leaders in the Pacific. Admiral Chester Nimitz advocated bypassing the Philippines in favor of capturing Formosa and Okinawa.

These would then be used as bases for attacking the Japanese home islands. This plan was countered by General Douglas MacArthur, who wished to fulfill his promise to return to the Philippines as well as land on Okinawa. After a lengthy debate involving President Roosevelt, MacArthur's plan was chosen. The first step in liberating the Philippines was the capture of Peleliu in the Palau Islands. Planning for invading the island had already begun as its capture was required in both Nimitz and MacArthur's plans.

On September 15, the 1st Marine Division stormed ashore. They were later reinforced by the 81st Infantry Division, which had captured the nearby island of Anguar. While planners had originally thought that the operation would take several days, it ultimately took over two months to secure the island as its 11,000 defenders retreated into the jungle and mountains. Utilizing a system of interconnected bunkers, strong points, and caves, Colonel Kunio Nakagawa's garrison exacted a heavy toll on the attackers and the Allied effort soon became a bloody grinding affair. On November 25, 1944, after weeks of brutal fighting that killed 2,336 Americans and 10,695 Japanese, Peleliu was declared secure.

Battle of Leyte Gulf

After extensive planning, Allied forces arrived off the island of Leyte in the eastern Philippines on October 20, 1944. That day, Lieutenant General Walter Krueger's U.S. Sixth Army began moving ashore. To counter the landings, the Japanese threw their remaining naval strength against the Allied fleet. To accomplish their goal, Toyoda dispatched Ozawa with four carriers (Northern Force) to lure Admiral William "Bull" Halsey's U.S. Third Fleet away from the landings on Leyte. This would allow three separate forces (Center Force and two units comprising Southern Force) to approach from the west to attack and destroy the U.S. landings at Leyte. The Japanese would be opposed by Halsey's Third Fleet and Admiral Thomas C. Kinkaid's Seventh Fleet.

The battle that ensued, known has the Battle of Leyte Gulf, was the largest naval battle in history and consisted of four primary engagements. In the first engagement on October 23-24, the Battle of the Sibuyan Sea, Vice Admiral Takeo Kurita's Center Force was attacked by American submarines and aircraft losing a battleship,  Musashi, and two cruisers along with several others damaged. Kurita retreated out of range of U.S. aircraft but returned to his original course that evening. In the battle, the escort carrier USS Princeton (CVL-23) was sunk by land-based bombers.

On the night of the 24th, part of the Southern Force led by Vice Admiral Shoji Nishimura entered the Surigao Straight where they were attacked by 28 Allied destroyers and 39 PT boats. These light forces attacked relentlessly and inflicted torpedo hits on two Japanese battleships and sank four destroyers. As the Japanese pushed north through the straight, they encountered the six battleships (many of them Pearl Harbor veterans) and eight cruisers of the 7th Fleet Support Force led by Rear Admiral Jesse Oldendorf. Crossing the Japanese "T", Oldendorf's ships opened fired at 3:16 AM and immediately began scoring hits on the enemy. Utilizing radar fire control systems, Oldendorf's line inflicted heavy damage on the Japanese and sank two battleships and a heavy cruiser. The accurate American gunfire then forced the remainder of Nishimura's squadron to withdraw.

At 4:40 PM on the 24th, Halsey's scouts located Ozawa's Northern Force. Believing that Kurita was retreating, Halsey signaled Admiral Kinkaid that he was moving north to pursue the Japanese carriers. By doing so, Halsey was leaving the landings unprotected. Kinkaid was not aware of this as he believed Halsey had left one carrier group to cover the San Bernardino Straight. On the 25th, U.S. aircraft began pummeling Ozawa's force in the Battle of Cape Engaño. While Ozawa did launch a strike of around 75 aircraft against Halsey, this force was largely destroyed and inflicted no damage. By the end of the day, all four of Ozawa's carriers had been sunk. As the battle was concluding, Halsey was informed that the situation off Leyte was critical. Soemu's plan had worked. By Ozawa drawing away Halsey's carriers, the path through the San Bernardino Straight was left open for Kurita's Center Force to pass through to attack the landings.

Breaking off his attacks, Halsey began steaming south at full speed. Off Samar (just north of Leyte), Kurita's force encountered the 7th Fleet's escort carriers and destroyers. Launching their planes, the escort carriers began to flee, while the destroyers valiantly attacked Kurita's much superior force. As the melee was turning in favor of the Japanese, Kurita broke off after realizing that he was not attacking Halsey's carriers and that the longer he lingered, the more likely he was to be attacked by American aircraft. Kurita's retreat effectively ended the battle. The Battle of Leyte Gulf marked the last time the Imperial Japanese Navy would conduct large-scale operations during the war.

Return to the Philippines

With the Japanese defeated at sea, MacArthur's forces pushed east across Leyte, supported by the Fifth Air Force. Fighting through rough terrain and wet weather, they then moved north onto the neighboring island of Samar. On December 15, Allied troops landed on Mindoro and met little resistance. After consolidating their position on Mindoro, the island was used as a staging area for the invasion of Luzon. This took place on January 9, 1945, when Allied forces landed at Lingayen Gulf on the island's northwest coast. Within a few days, over 175,000 men were put ashore, and soon MacArthur was advancing on Manila. Moving quickly, Clark Field, Bataan, and Corregidor were retaken and pincers closed around Manila. After heavy fighting, the capital was liberated on March 3. On April 17, the Eighth Army landed on Mindanao, the second largest island in the Philippines. Fighting would continue on Luzon and Mindanao until the end of the war.

Battle of Iwo Jima

Located on the route from the Marianas to Japan, Iwo Jima provided the Japanese with airfields and an early warning station for detecting American bombing raids. Considered one of the home islands, Lt. General Tadamichi Kuribayashi prepared his defenses in depth, constructing a vast array of interlocking fortified positions connected by a large network of underground tunnels. For the Allies, Iwo Jima was desirable as an intermediate airbase, as well as a staging area for the invasion of Japan.

At 2:00 a.m. on February 19, 1945, U.S. ships opened fire on the island and aerial attacks began. Due to the nature of the Japanese defenses, these attacks proved largely ineffective. The next morning, at 8:59 a.m., the first landings began as the 3rd, 4th, and 5th Marine Divisions came ashore. Early resistance was light as Kuribayashi wished to hold his fire until the beaches were full of men and equipment. Over the next several days, American forces advanced slowly, often under heavy machine-gun and artillery fire, and captured Mount Suribachi. Able to shift troops through the tunnel network, the Japanese frequently appeared in areas that the Americans believed to be secure. Fighting on Iwo Jima proved extremely brutal as American troops gradually pushed the Japanese back. Following a final Japanese assault on March 25 and 26, the island was secured. In the battle, 6,821 Americans and 20,703 (out of 21,000) Japanese died. 

Okinawa

The final island to be taken before the proposed invasion of Japan was Okinawa. U.S. troops began landing on April 1, 1945, and initially met light resistance as Tenth Army swept across the south-central parts of the island, capturing two airfields. This early success led Lt. General Simon B. Buckner, Jr. to order the 6th Marine Division to clear the northern part of the island. This was accomplished after heavy fighting around Yae-Take.

While land forces were fighting ashore, the US fleet, supported by the British Pacific Fleet, defeated the last Japanese threat at sea. Named Operation Ten-Go, the Japanese plan called for the super battleship Yamato and the light cruiser Yahagi to steam south on a suicide mission. The ships were to attack the U.S. fleet and then beach themselves near Okinawa and continue the fight as shore batteries. On April 7, the ships were sighted by American scouts and Vice Admiral Marc A. Mitscher launched over 400 aircraft to intercept them. As the Japanese ships lacked air cover, the American aircraft attacked at will, sinking both.

While the Japanese naval threat was removed, an aerial one remained: kamikazes. These suicide planes relentlessly attacked the Allied fleet around Okinawa, sinking numerous ships and inflicting heavy casualties. Ashore, the Allied advance was slowed by rough terrain and stiff resistance from the Japanese fortified at the southern end of the island. Fighting raged through April and May as two Japanese counteroffensives were defeated, and it was not until June 21 that resistance ended. The largest land battle of the Pacific war, Okinawa cost the Americans 12,513 killed, while the Japanese saw 66,000 soldiers die.

Ending the War

With Okinawa secured and American bombers regularly bombing and firebombing Japanese cities, planning moved forward for the invasion of Japan. Codenamed Operation Downfall, the plan called for the invasion of southern Kyushu (Operation Olympic) followed by seizing the Kanto Plain near Tokyo (Operation Coronet). Due to the geography of Japan, the Japanese high command had ascertained Allied intentions and planned their defenses accordingly. As planning moved forward, casualty estimates of 1.7 to 4 million for the invasion were presented to Secretary of War Henry Stimson. With this in mind, President Harry S. Truman authorized the use of the new atom bomb in an effort to bring a swift end to the war.

Flying from Tinian, the B-29 Enola Gay dropped the first atom bomb on Hiroshima on August 6, 1945, destroying the city. A second B-29, Bockscar, dropped a second on Nagasaki three days later. On August 8, following the Hiroshima bombing, the Soviet Union renounced its nonaggression pact with Japan and attacked into Manchuria. Facing these new threats, Japan unconditionally surrendered on August 15. On September 2, aboard the battleship USS Missouri in Tokyo Bay, the Japanese delegation formally signed the instrument of surrender ending World War II.

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Hickman, Kennedy. "Island Hopping in World War II: A Path to Victory in the Pacific." ThoughtCo, Jun. 4, 2017, thoughtco.com/world-war-ii-across-the-pacific-2361460. Hickman, Kennedy. (2017, June 4). Island Hopping in World War II: A Path to Victory in the Pacific. Retrieved from https://www.thoughtco.com/world-war-ii-across-the-pacific-2361460 Hickman, Kennedy. "Island Hopping in World War II: A Path to Victory in the Pacific." ThoughtCo. https://www.thoughtco.com/world-war-ii-across-the-pacific-2361460 (accessed November 24, 2017).