Pacific Carrier War: Carrier Combat from Pearl Harbor to Okinawa

By Mark Stille

A detailed and comprehensive study of the carrier formations of the Pacific War, including their origins, development and key battles from the Coral Sea, through Midway and Guadalcanal to the battle of the Philippine Sea.

The defining feature of the Pacific Theatre of World War II was the clash of carriers that ultimately decided the fate of nations. The names of these battles have become legendary as some of the most epic encounters in the history of naval warfare.

Pre-war assumptions about the impact and effectiveness of carriers were comprehensively tested in early war battles such as Coral Sea, while US victories at Midway and in the waters around Guadalcanal established the supremacy of its carriers. The US Navy's ability to adapt and evolve to the changing conditions of war maintained and furthered their advantage, culminating in their comprehensive victory at the battle of the Philippine Sea, history's largest carrier battle, which destroyed almost the entire Japanese carrier force.

Examining the ships, aircraft and doctrines of both the Japanese and US navies and how they changed during the war, Mark E. Stille shows how the domination of American carriers paved the way towards the Allied victory in the Pacific.

• Language: English
• Publisher: Bloomsbury Publishing
• Release date: Oct 14, 2021
• ISBN: 9781472826350

Mark Stille

Mark Stille is the author of numerous Osprey titles focusing on naval history in the Pacific. He recently concluded a nearly 40-year career in the intelligence community, including tours on the faculty of the Naval War College, on the Joint Staff and on US Navy ships. He received his BA in History from the University of Maryland and also holds an MA from the Naval War College.

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INTRODUCTION

It would be an exaggeration to say that the Pacific War was decided by the five carriers that fought during the conflict, but perhaps not much of an exaggeration. At the start of the war, both sides still largely believed that a decisive battle between the Imperial Japanese Navy (IJN) and the United States Navy (USN) would be determined by a climactic clash of battleships. This view was not universally held within each navy, as shown by the Japanese creation of an independent carrier force – the First Air Fleet – in April 1941, and prewar American experimentation with independent strike groups built around carriers. Both sides recognized the importance of naval air power, and both had built very different carrier forces.

Facing a numerical disadvantage created by the interwar system of naval treaties and Japan’s industrial inferiority, the IJN created a carrier force based on achieving a qualitative edge over the USN. This edge was created by establishing a cadre of highly trained aviators – the most highly trained in the world – and designing aircraft capable of striking at longer ranges than their American counterparts. Creation of the First Air Fleet was a force multiplier since, by the summer of 1941, it combined six fleet carriers into a single operational entity. This ability to mass naval air power was a game changer, as demonstrated at Pearl Harbor and other places during the opening months of the war. Had the Japanese maintained the cohesion of the First Air Fleet during this initial period, the history of the war would have turned out much differently.

As the Japanese massed naval air power, the Americans still operated carriers singly. Some American admirals saw the benefits of massing multiple carriers into a single task force, but most preferred to keep them separated to avoid detection and destruction. Operating singly, or even in pairs, American carriers lacked the striking power of the First Air Fleet. Also impacting their striking power was the short range of American carrier aircraft and the almost total ineffectiveness of the standard torpedo bomber and its torpedo.

The IJN’s carrier force had a predictable run of successes in the first few months of the war. Their apparent smashing victory at Pearl Harbor was followed by more success at Rabaul, the Dutch East Indies, Darwin, Australia, and finally by a massive raid into the Indian Ocean. However, the only time during the war that the Japanese operated all six of their prewar fleet carriers in a single formation was at Pearl Harbor. This lack of concentration gave the Americans an opportunity to defeat the First Air Fleet piecemeal. The First Air Fleet was set up for destruction by bad operational planning by the most overrated admiral of the war – Yamamoto Isoroku – not by a lack of tactical prowess.

At the battle of the Coral Sea, American Admiral Chester Nimitz aggressively sought an opportunity to engage the Japanese carrier force. The appearance of American carriers in the South Pacific in March 1942 forced the Japanese to send carriers to the region to protect any further advances. To cover his next operation, Yamamoto allocated only two fleet carriers and a light carrier to seize Port Moresby. For his part, Nimitz was prepared to send all four of his operational carriers to the South Pacific, but the raid on Tokyo held up two carriers, leaving only two to deal with the massive Japanese incursion into the Coral Sea. The resulting first carrier battle was a very confused affair with both sides having and wasting opportunities to launch an all-important first strike. When the preliminaries were over, both sides finally struck the other’s main carrier force on May 8, 1942. The exchange was deadly, but the prewar notion that carriers were extremely vulnerable to air attack was proven incorrect. One American fleet carrier was sunk, and another damaged. Japanese losses were much heavier. The light carrier was sunk, one of the fleet carriers bombed and heavily damaged, and the second fleet carrier had its air group so attrited that it was considered by the Japanese to be incapable of operations. Thus, of the 11 IJN carriers operational before the battle, only eight remained available for the next, and most famous, carrier battle.

The battle of the Coral Sea was just a preface to Yamamoto’s major operation the following month. This operation was targeted on Midway Atoll but was actually focused on annihilating Nimitz’s remaining strength in a decisive battle. Through a series of astoundingly bad decisions, the remaining four Japanese fleet carriers were actually outnumbered at the point of contact against Nimitz’s three fleet carriers and the many aircraft stationed on Midway. Using exquisite intelligence, and insightfully positioning their carriers where they could strike the Japanese, the Americans pulled off the only successful ambush during any of the war’s carrier battles. Despite major issues in coordination and communication that threatened to derail Nimitz’s ambush, fate placed the Americans’ most powerful weapon, their dive-bombers, over the Japanese carriers at the point they were most vulnerable. The result was the bombing of three carriers within the span of minutes, all of which later sank. A single remaining Japanese fleet carrier acquitted itself well, heavily damaging an American carrier that was later finished off by an American submarine, before it was also sunk. The battle of Midway was not the kind of decisive battle that Yamamoto was planning for. At its conclusion, the IJN’s offensive power in the Pacific was blunted. But it was not the end of the IJN’s carrier force, as is often suggested.

Following their victory at Midway, the Americans were quick to seize the strategic initiative in the Pacific. To protect the sea lines of communication between the United States and Australia, and to begin the counteroffensive to recapture Rabaul, which had become the main Japanese bastion in the South Pacific, American attentions turned to the South Pacific. The hastily prepared first American offensive of the entire war selected the island of Guadalcanal in the southern Solomons for invasion because the Japanese were building an airfield there. Control of this airfield was critical to the outcome of the campaign, which stretched to six months and extracted heavy losses from both sides.

During the campaign, the Americans used their carriers to defend against major Japanese efforts to recapture the island. There were only two carrier battles over the span of six months. In the first, the battle of the Eastern Solomons, carrier forces of equal size fought a very cautious and indecisive battle. In the process, Yamamoto’s first poorly planned attempt to throw the American invasion force off the island was defeated. The second carrier battle was the result of the largest Japanese effort of the campaign to retake the airfield with a land offensive and then destroy American naval forces around the island. This encounter, the battle of Santa Cruz, is the least well understood of the war’s carrier battles. It was also the only time during the war that the Japanese carriers gained a clear victory. However, in doing so, Japanese aircraft losses were so high they were unable to follow up their victory. Throughout the battle, control of the airfield on Guadalcanal was the path to victory. The Japanese were never able to suppress the airfield for any extended period to allow them to move large ground forces to the island and supply them for an offensive to capture the airfield. Carriers on both sides played supporting, but important, roles during the Guadalcanal campaign.

Both carrier forces were exhausted after Guadalcanal. For the next 18 months, the Japanese tried to rebuild their carrier force. This effort was unsuccessful in many areas. Japanese industry only completed a single purpose-built carrier during this period and failed to design and produce carrier aircraft with dramatically better performance than those that had populated the IJN’s flight decks at the start of the war. Even more difficult was the process of training new aviators with anything like the skills of those from the beginning of the war. This reflected the heavy losses from the four carrier battles in 1942 and the subsequent commitment of the rebuilt carrier air groups into the defense of the central and northern Solomons in the second half of 1943. Most of all, the IJN proved unable to harness new technologies to the same degree as did the USN. For the last carrier battle of the war in June 1944, the IJN fought with an inferior version of the force with which they had begun the war.

While the Japanese tried to rebuild their carrier fleet for another attempt to fight a decisive battle, the Americans produced a carrier force much more powerful and capable than had ever before been seen in any of the world’s oceans. This was demonstrated in a series of campaigns from late 1943 until the battle of the Philippine Sea in mid-1944. When the last carrier battle was fought following the American invasion of Saipan, the outcome was preordained. Not only did the USN possess a marked numerical and qualitative advantage, but its new carrier doctrine was able to defeat a massive Japanese initial blow, something that had been impossible in 1942. Philippine Sea was the most crushing loss for the IJN of any carrier battle during the war; it was even more decisive than Midway since, after the battle, the Japanese no longer had any ability to build a viable carrier force to contend with the next American advance.

That next advance came at Leyte in the Philippines four months later. Yet again, the IJN made plans for a decisive battle. This time the state of the IJN’s carrier force made it suitable only as a decoy force. The centerpiece of the plan to turn back the American invasion fell upon the IJN’s still-powerful force of battleships and heavy cruisers. The battle of Leyte Gulf included four major actions. In one of these, a small strike from the remaining Japanese carriers attacked an American carrier task force. So weak was the strike that the Americans did not even recognize it as the final Japanese carrier strike of the war. The next day the might of the American carriers was turned on the Japanese carrier force. This was not a carrier battle, but rather a maritime execution. Without air cover, and for other reasons, the Japanese operation at Leyte was doomed to defeat. The principal vehicle to their defeat was the USN’s carrier force. Over the course of three days, and in spite of poor command decisions that hamstrung its operations and effectiveness, American carriers launched the greatest number of offensive air sorties in naval history at the Japanese force of heavy combatants while still striking the Japanese carrier force and sinking every one of its four carriers. While the Japanese plan at Leyte Gulf contained a clever aspect of using its carriers as a diversion to lure the American carrier force out of position, it still resulted in such a defeat that the IJN never mounted another major operation during the war. Even these crippling losses resulted in no delay to the American advance.

After Leyte Gulf, the IJN chose to resort to suicide attacks, epitomized by the kamikaze.

These caused mayhem and death, even against well-defended American aircraft carriers, but proved unable to turn the tide against the USN or even to delay its final advance to Japan. In spite of the kamikaze threat, the USN’s carrier force operated continually off Okinawa for some three months, ensuring the invasion would succeed. From there, the carriers embarked on a series of large-scale raids on the Japanese homeland. From the first raid on Japan in April 1942 with 16 army bombers launched from a single carrier, American carriers were able to mount strategic attacks with thousands of sorties over several days from almost 20 carriers. The combination of massive production of ships and aircraft, added to excellent training and a proven doctrine, all supported by logistics on an unprecedented scale, made the American carrier force a war-winning weapon. The Pacific Carrier War had come full cycle from the opening day of the conflict at Pearl Harbor.

CHAPTER 1

SHIPS, AIRCRAFT, AND MEN

THE IMPERIAL JAPANESE NAVY (IJN) CARRIER FORCE

The IJN was quick to appreciate the potential of carrier aviation, and commissioned its first small carrier in 1922. Two more large carriers followed in 1927 and 1928. Early carrier aircraft missions included scouting and spotting the fall of shot from the battle line. By the end of the 1920s, the use of fighter aircraft to cover the battle line and to gain control of the airspace over the enemy’s battle line was emphasized. This largely defensive focus was due mainly to the inability of early attack aircraft to carry large payloads that compromised their ability to attack heavily armored battleships. As better aircraft and weapons were developed, Japanese carriers were increasingly seen as offensive platforms with American carriers as their principal targets. Neutralizing enemy carriers ensured air dominance over the battle area. This could be accomplished by sinking American carriers or, more easily, by wrecking their flight decks. The Japanese believed that enemy carriers were vulnerable to dive-bombing (compared to horizontal bombing) since this method offered the possibility of precision attacks. Torpedo attacks were considered necessary to sink enemy carriers and other large warships, and by the late 1930s the IJN had developed both dive-bombing and torpedo attack tactics. Like every other component of the Imperial Navy, Japanese carriers were designed and trained for offensive warfare. In the case of carrier combat, the essential precondition for victory was to find the enemy’s carriers first and launch overwhelming strikes as quickly as possible. Ideally the attacks would be executed beyond the range from which the enemy could retaliate. This doctrine explained the great Japanese emphasis on large carrier air groups composed of aircraft uniformly lighter than their opponents, giving them greater range.

The Imperial Navy’s first carrier was Hosho, shown here on trials in November 1923. The small island proved unsuccessful and was removed the following year, but the ship gave invaluable service as a test platform for flight operations at sea. (Yamato Museum)

Prior to the war, Japanese carriers operated as divisions in a semi-independent but strictly adjunct role to the fleet they were assigned to. As carriers were assessed to be extremely vulnerable to attack, dispersal seemed to increase their prospects of survival since only a portion of friendly carriers could be detected and attacked. In 1940 aviation advocates began to press the Commander of the Combined Fleet, Admiral Yamamoto Isoroku, to concentrate the existing carrier divisions into a single command to form an air fleet which could train and fight together. Concentration offered both the potential of greater offensive power by launching larger strikes with better prospects for coordinating attacks and increased defensive capabilities by massing fighters and antiaircraft fire.

Accordingly, the First Air Fleet was established in April 1941. It was commanded by a non-aviator (which was the norm in the IJN), Vice Admiral Nagumo Chuichi, and was composed of three carrier divisions: Carrier Division 1 included the large fleet carriers Akagi and Kaga; Carrier Division 2 was assigned fleet carriers Soryu and Hiryu; Carrier Division 3 possessed only the old Hosho and the light carrier Ryujo. Immediately before the war, carriers Shokaku and Zuikaku were commissioned and formed Carrier Division 5.

One important advantage exercised by the Japanese at the start of the war was their ability to mass carrier air power. The Kido Butai (literally Mobile Force but better translated as Striking Force) was the operational component of the First Air Fleet. Unlike in the US Navy, where the carrier division served only in an administrative capacity, the carrier divisions of the Kido Butai were operational entities. Air groups from the division’s carriers routinely trained and fought together. During multiple carrier operations, the entire strike would be commanded by one of the carrier group commanders who would direct the operations. For a major strike, one carrier division would typically contribute its dive-bomber squadrons and another carrier division its torpedo squadron. This allowed a quick launch of the strike, since all the aircraft could be parked on the flight deck without the need to spot another group of aircraft on the flight deck and prepare it for launch. Typically, the strike was accompanied by an escort of six to nine fighters from each carrier. The creation of the First Air Fleet was revolutionary in concept. It gave the Japanese the means to mass air power at any spot in the Pacific. This mass of Japanese air power comprised high-quality aircraft flown by skilled aviators which enabled the IJN to overwhelm Allied defenses early in the war.

Akagi photographed in 1939 after modernization. Assigned to Carrier Division 1, she was also the flagship of the Kido Butai until being sunk at Midway in June 1942. As a converted battlecruiser, she was fast, well protected, and able to embark a large air group. (Naval History and Heritage Command)

Kaga shown in 1936 after her major reconstruction. Note the smoke exhaust aft of the island which was angled toward the water to avoid placing smoke over the flight deck. She was the largest of the IJN’s prewar carriers, having been converted from a battleship. (Naval History and Heritage Command)

THE SHIPS

The IJN began the war with the world’s largest fleet of aircraft carriers. Japanese interest in carriers began as early as 1914 and benefited from a Royal Navy mission in Japan from 1921 to 1923 to assist in naval aviation. The Washington Naval Treaty of 1922 had a great impact on future Japanese carrier design and construction. Under the treaty, total Japanese carrier tonnage was restricted to 81,000 tons compared with the US Navy’s 135,000 tons. Individual ships could not displace over 27,000 tons, but the conversion of two existing capital ships was permitted with a maximum tonnage of 33,000. This position of inferiority forced the Japanese into several schemes in order to maintain numerical parity with the Americans. At the end of 1936, Japan left the naval treaty system and was thereafter free to build carriers as it desired.

The first Japanese carrier, Hosho, was commissioned in December 1922. This small carrier was key in the early days of carrier development but by the start of the war was of marginal utility. After participating in the Midway operation, Hosho was used as a training carrier for the remainder of the war.

Akagi was one of the two capital ships permitted to be converted into carriers under the terms of the Washington Naval Treaty. Converted from a battlecruiser, Akagi was fast and well protected with the capacity to carry a large number of aircraft. The other capital ship conversion was Kaga. Since Kaga was originally a battleship, she was slower than Akagi but her larger hull allowed for a greater aircraft capacity.

After the conversion of Akagi and Kaga, the IJN only had 30,000 tons left of its treaty allotment for carrier construction. At this point the Japanese began to get imaginative. Under the terms of the treaty, carriers under 10,000 tons were exempt from tonnage calculations. Accordingly, the IJN planned to build an 8,000-ton ship able to embark 24 aircraft. Before construction began, the Japanese decided that 24 aircraft was insufficient, so the design was recast with a second hangar deck in order to embark 48 aircraft. Not surprisingly the new design came in at 12,500 tons, which not only placed it well over treaty restrictions but also created severe stability problems. Ryujo underwent two rebuilds before the war to correct design defects and, despite having a nominal aircraft capacity of 48, only embarked 26 at the start of the war.

Ryujo pictured underway in September 1938 after her two major rebuilds to correct stability issues. Even when these were complete, she possessed limited effectiveness because of her small flight deck, small elevators, and poor elevator placement which hindered efficient flight operations. (Naval History and Heritage Command)

The first Japanese ship designed as a carrier from the keel up was Soryu. She epitomized the Japanese preference for a carrier with a large aircraft capacity on a fast, light hull. Hiryu’s design was based on Soryu’s but used the extra displacement to improve protection and create a greater beam that improved stability. Hiryu was considered very successful and became the template for the Shokaku and the late war Unryu classes.

Just as the Yamato-class superbattleships were designed to create a qualitative overmatch against their American counterparts, the Japanese intended the same to be true for the Shokaku-class carriers (Shokaku and Zuikaku), laid down in 1937 after treaty restrictions had ended. The design was an enlarged Hiryu with much better protection, range, and aircraft capacity. The two ships were the best Japanese carriers of the war and superior to any other aircraft carrier in the world until the arrival of the American Essex class in 1943.

In another effort to evade treaty restrictions, the IJN launched a number of ships before the war which were designed to be easily converted into carriers when the need arose. The first two were originally intended as high-speed oilers and then were redesigned as submarine tenders. As carriers the two ships were known as the Shoho class. They proved to be useful conversions but lacked any protection and possessed a mediocre top speed. More useful were the two ships of the Hiyo class which were laid down in 1939 as large passenger liners. Conversion began in February 1941, and both ships entered service the following year. To increase speed, a hybrid propulsion system of destroyer-type boilers mated to merchant turbines was used, but this proved troublesome in service and top speed remained marginal. However, the ships were able to embark an air group of 48 aircraft.

This is Hiryu on trials in April 1939. The extra tonnage allotted to her design produced a much more balanced ship compared with the relatively unprotected Soryu. Hiryu was the basis for the highly successful Shokaku class. Since it was easier to mass produce than the larger Shokaku class, the Japanese returned to Hiryu’s design in 1942 for the Unryu class, of which six ships were laid down in 1942 and 1943. However, only three Unryu-class ships were completed and none ever launched an aircraft against the Americans in combat. (Naval History and Heritage Command)

Soryu photographed in January 1938 during sea trials. Her design epitomized the Japanese preference for a fast carrier able to embark a large air wing, giving it maximum offensive potential. (Naval History and Heritage Command)

Shokaku was the first Japanese carrier built without regard to treaty limitations and was an unqualified success. The two ships of this class were the most powerful carriers in the world until the arrival of the USN’s Essex class in late 1943. This is Shokaku after completion in August 1941. (Naval History and Heritage Command)

Zuikaku photographed in September 1941 after completion. Of the six carriers which participated in the Pearl Harbor operation, Zuikaku had the longest career and was not sunk until October 1944. (Naval History and Heritage Command)

Japanese carriers possessed marginal antiaircraft capabilities. The standard long-range antiaircraft gun was the Type 89 5-inch High-Angle Gun that equipped almost all Japanese carriers of the period. The weapon itself was adequate with fairly high elevating speeds, a high muzzle velocity, and a 51lb shell. However, the weapon was handicapped by its fire-control director, the Type 94 High-Angle Firing Control Installation. It was simply too slow to generate fire-control solutions on high-speed targets like American carrier aircraft. This placed the burden of shipboard air defense on the Type 96 25mm antiaircraft gun. This weapon was standard on all Japanese carriers and was fitted in both dual and triple mounts. Unfortunately for the Japanese, the Type 96 was a mediocre weapon and ineffective in its assigned role. It had an effective range of only 1,635 yards, was slow in training and elevation, had a low sustained rate of fire, and produced excessive blast and vibration which affected its accuracy. Also, its fire-control director, the Type 95 Short-Range High-Angle Director, could not handle high-speed targets. No Japanese carrier began the war equipped with radar.

One of the ways the Imperial Navy devised to escape treaty restrictions on carrier tonnage was to build a fleet of auxiliaries which could be quickly converted into carriers. Shoho, shown here in December 1941 after her conversion was completed, was the first of these ships. (Yamato Museum)

Zuiho was a light carrier conversion capable of embarking an air group of some 30 aircraft. She saw extensive service and was present at two of the carrier battles of 1942 and at Philippine Sea in 1944. (Yamato Museum)

Junyo photographed in Kure taking on fuel on May 3, 1944. Note the ship’s large island and angled stack. Also noticeable is the mercantile lines of her hull, which betray her origin as a passenger liner. Despite her shortcomings, Junyo and sister ship Hiyo were valuable additions to the IJN’s carrier fleet. (Yamato Museum)

THE AIRCRAFT

At the start of the war, Japanese fleet carriers were equipped with three types of aircraft which paralleled the organization of the ships’ air groups. The fighter squadron was assigned the Mitsubishi A6M2 Navy Type 0 Carrier Fighter Model 21. It was generally referred to as simply the Zero as it will be here. Initial design specifications were issued by the IJN in 1937 with the first variant, the A6M1, taking flight in April 1939. This model was underpowered, so the next variant was given a more powerful 950hp engine and a legend was born. The A6M2 variant was the early war standard for both Japanese carrier and land-based fighter units. The designers had succeeded in meeting a very challenging set of design specifications for a long-range, maneuverable, and heavily armed fighter. The Zero was known for its strengths of unparalleled range, exceptional maneuverability, and great climb and acceleration. In a classic dogfight it was nearly invincible. However, the desire to make the airframe as light as possible came with a