Ryuho

The IJN Ryuho: A Converted Carrier’s Struggle in World War II

The Japanese Navy converted the submarine tender Taigei into a light aircraft carrier which they named Ryuho and took into service during November 1942 when the Pacific War was reaching a crucial phase. In an urgent response to the four fleet carriers sunk at Midway Japan converted auxiliary ships like Ryuho to restore its carrier strength. Due to its design flaws and slow speed along with weak construction Ryuho served only as a support vessel for aircraft transport and pilot training while participating in the Battle of the Philippine Sea. The narrative of Ryuho illustrates how the IJN struggled with limited resources while trying to use civilian ships for current naval warfare needs. This article explores Ryuho’s design elements and special features while highlighting its important yet restricted World War II functions by analyzing historical documents and evaluative viewpoints to determine its impact.

Design and Construction

Ryuho began its existence as the submarine tender Taigei which was laid down at the Yokosuka Naval Arsenal on April 12, 1933. Japan commissioned Taigei on March 31, 1934 after its November 16, 1933 launch to serve as a support vessel for its submarine fleet with an optimized hull for stability and fuel efficiency instead of combat capabilities. The Japanese government designed Taigei with provisions to convert it into an aircraft carrier in response to capital ship restrictions imposed by the 1930 London Naval Treaty and to prepare for future wartime requirements. The Japanese Navy began Taigei's transformation into a light carrier after the attacks on Pearl Harbor and the disaster at Midway during June 1942. On November 30, 1942 the ship became Ryuho with Captain Kamei Yoshio assuming command.

The design of Ryuho showed its roots in auxiliary ship construction because it came with major limitations in battle effectiveness. The ship reached a length of 215.65 meters and had a beam of 19.58 meters with a draft of 6.67 meters. The standard displacement of the ship was 13,360 tons but reached 16,700 tons when fully loaded. The ship used two geared steam turbines along with six boilers to achieve 52,000 shaft horsepower which enabled a maximum speed of 26.5 knots but was slower than fleet carriers such as the Shokaku that reached 34 knots. The vessel could travel about 8,000 nautical miles while maintaining a speed of 18 knots. Initially equipped with eight 12.7 cm/40 Type 89 dual-purpose guns in four twin mounts and twenty-eight 25 mm Type 96 anti-aircraft guns mounted singly and in threes, the ship later increased its anti-aircraft armament to sixty-one guns by 1944. The Ryuho had a capacity range of 31 to 36 aircraft which included Mitsubishi A6M Zero fighters and Aichi D3A Val dive bombers plus Yokosuka D4Y Suisei dive bombers as well as Nakajima B5N Kate or B6N Tenzan torpedo bombers. Minimal armor protection included no substantial belt or deck defenses while the hull kept civilian-grade steel which made it susceptible to torpedoes and bomb attacks. The number of officers and enlisted personnel aboard the crew reached nearly 989.

The conversion process was fraught with challenges. The aircraft carrier's stability problems worsened after engineers added a flight deck and hangar that resulted in increased top weight. The shipbuilders installed bulges to enhance buoyancy while these modifications slowed the vessel. By August 1944 the flight deck lengthened from 185 meters to 198.1 meters to fit bigger aircraft though the hangar size restricted the number of planes that could be stored onboard. The bridge placement below the flight deck served as a protective measure against direct hits but created difficulties in navigation. The propulsion system of Ryuho could not handle the additional weight efficiently while its unprotected underwater sections allowed for easy torpedo damage during service operations. Historian Mark Stille identifies Ryuho as one of the least successful conversions of Japanese Navy carriers in his work Imperial Japanese Navy Aircraft Carriers 1921–1945 because of its design flaws.

What Made Ryuho Special

Ryuho stood out due to its creation as a convertible auxiliary vessel which served as a strategic solution to naval treaty restrictions. Japan's IJN designed Taigei for carrier conversion which enabled the quick buildup of their carrier fleet following Midway despite producing suboptimal outcomes. Japan's industrial limitations became evident through the pragmatic adaptability demonstrated by their reliance on convertible vessels since purpose-built aircraft carriers such as Taiho demanded several years to build. The versatility of Ryuho which allowed it to function as an aircraft transporter and training platform while also engaging in combat operations made it an indispensable asset to a depleted navy in 1943.

IJN carriers featured a unique below-deck bridge design that minimized vulnerability to air attacks but made command and control operations more difficult. Ryuho's compact size together with this specific feature enabled operations in narrow sea areas like Japan’s Inland Sea for training exercises and transportation tasks. Multiple attacks including a torpedo strike in 1942 and air raids in 1945 demonstrated the ship’s resilience even though it had weak structural integrity. During the Doolittle Raid on April 18, 1942 Taigei received hits from one 500-pound bomb and thirty incendiary bombs but maintained minimal damage and only seven casualties which enabled repair work to begin.

However, Ryuho’s limitations were glaring. The ship could not operate effectively with fleet operations because of its slow speed and its air group consisting of fewer than 36 aircraft could not match the power of bigger carriers. Combat effectiveness declined further in 1944 due to the depletion of seasoned pilots during the battle at Philippine Sea. Historian Paul S. Dull explains Ryuho served only auxiliary functions because its poor operational performance forced it to take over Hosho's training duties whenever the older carrier was under maintenance. Ryuho stood as a representation of Japan's last-minute efforts to adapt while demonstrating the decreasing effectiveness of its conversion initiative.

Key Roles in Major Battles

Early Operations and the Doolittle Raid (1942)

The ship Taigei sustained damage from the Doolittle Raid while docked at Yokosuka on April 18, 1942 which caused Ryuho to enter wartime service before its conversion was finished. Lt. Edgar E. McElroy piloted a B-25 Mitchell bomber that released a single 500-pound bomb onto the bow and thirty incendiary bombs which inflicted light damage and resulted in seven casualties. Owing to the attack Ryuho needed repairs on its burned and damaged parts which Captain Soma Shinshiro supervised before completion. Upon completion of its commissioning on November 30, 1942 Ryuho joined the 3rd Fleet and served as a reserve ship at the Maizuru Naval District. During its initial deployment in December 1942 Ryuho transported twenty light bombers with their respective crews from Japan to Truk in the Caroline Islands where it served as a critical IJN base. A torpedo attack from USS Drum on December 12 hit Ryuho on its starboard side which necessitated its return to Yokosuka for repairs until March 1943. The initial events revealed Ryuho's susceptibility and restricted its early activities to support operations outside of combat.

Aircraft Ferrying and Training (1943)

During 1943 Ryuho served as an aircraft transport vessel and pilot training ship which showed it was not fit for fleet operations. The ship began its aircraft transport missions to locations across Japan and Southeast Asia on March 13, 1943. While servicing with the Second Carrier Division of the 3rd Fleet Ryuho performed pilot training near the Mariana Islands which became crucial because Japan suffered increasing pilot casualties. The Ryuho operated with a small air contingent of 21 A6M2 Zero fighters and nine B5N Kate torpedo bombers in June 1943 which demonstrated its restricted operational capacity. The missions served to maintain Japan’s air defense capabilities throughout the Pacific especially in the Solomon Islands and Central Pacific despite their non-combat nature. Because of Ryuho’s slow speed and weak armament the ship only participated in escorted convoys and steered clear of direct combat engagements during that time.

Battle of the Philippine Sea (June 1944)

During the Battle of the Philippine Sea in the Mariana Islands campaign Ryuho saw its most important combat action on June 19–20, 1944. Vice Admiral Jisaburo Ozawa’s Mobile Fleet assigned Ryuho to “Force B” where it operated with carriers Hiyo and Junyo, battleship Nagato, cruiser Mogami, and eight destroyers. The Japanese Imperial Navy planned to eliminate the U.S. Fifth Fleet’s Task Force 58 which provided support for operations on Saipan, Tinian, and Guam. Ryuho operated with 36 aircraft consisting of nine A6M2 Zero fighters, 18 A6M5 Zeros and nine B6N Tenzan torpedo bombers while facing pilot shortages because of Japan’s high rate of pilot losses. As part of Operation A-Go Ryuho executed an air strike against Task Force 58 on June 19. The Ryuho air group located their targets but failed to score any hits while suffering devastating losses during the “Great MarianAS Turkey Shoot” as nearly all of its aircraft were destroyed by U.S. F6F Hellcat fighters or Task Force 58’s anti-aircraft barrage.

Four Grumman TBF Avenger torpedo bombers from USS Enterprise launched a direct assault on Ryuho at 18:10 on June 20. Despite suffering moderate concussion and shrapnel damage from near-miss attacks the ship endured minor below-deck bridge damage which permitted continued operations. The IJN faced a catastrophic defeat when Hiyo, Shokaku, and Taiho were sunk and all aircraft from Ryuho's air group were destroyed. Without aircraft Ryuho had to return to Japan to perform patrol and training missions because its role in combat operations ceased. During the Philippine Sea encounter Ryuho demonstrated its operational weaknesses through its limited air force and pilot inexperience which proved ineffective against the superior technology and numbers of the United States forces.

Later Service and Fate (1944–1945)

Ryuho served as an aircraft transport after its battles in the Philippine Sea ended its frontline service. The ship restarted its transportation mission on October 25, 1944 when it transported aircraft from Sasebo, Japan to Keelung, Taiwan. Between November 7 and November 15 of 1944, Ryuho performed the brief flagship duties for Admiral Ozawa which symbolized its diminished operational role. On December 31, 1944, Ryuho completed its last operation carrying 58 Ohka special attack planes to Taiwan while destroyers Hamakaze, Isokaze, Yukikaze, Shigure, and Hatakaze provided escort and nine oil tankers headed to Singapore followed in tow. A formation of 12 TBF Avengers attacked Ryuho but failed to score hits while Ryuho's anti-aircraft weapons managed to shoot down one bomber. After the Battle of Leyte Gulf the Japanese navy no longer deployed any carriers outside their home waters.

Ryuho stayed immobilized in Japan's Inland Sea during 1945 due to fuel shortages and persistent U.S. air raids. U.S. air assaults in July 1945 resulted in extensive damage to Kure which rendered the ship inoperable. The Japanese carrier Ryuho remained inoperable and captured in September 1945 before it was scrapped in 1946. The survival of the ship until the war’s conclusion showed the dedication of its crew yet revealed the Japanese Imperial Navy's shortcomings in combat deployment.

Critical Analysis

The flawed design of Ryuho combined with strategic errors from the IJN restricted its operational effectiveness. Ryuho participated solely in the Battle of the Philippine Sea before being rendered ineffective by the destruction of its air group which demonstrated how poorly prepared pilots could not withstand stronger American forces. Ryuho functioned as an aircraft transport and training platform to support Japan's air defense efforts during the war yet its slow speed and poor construction hindered it from achieving the same level of impact as carriers such as Zuikaku. Though the Ryuho ship displayed resilience by surviving several attacks including the Doolittle Raid and kamikaze strikes its inadequate armor and lack of underwater defenses created significant vulnerabilities during fleet operations.

Sources like the Dictionary of American Naval Fighting Ships and Morison’s History of United States Naval Operations in World War II describe Ryuho as a minor participant in the conflict led by the United States. Japanese accounts including A Battle History of the Imperial Japanese Navy by Paul S. Dull point out that vessels served well in secondary functions but failed in direct combat situations. Military analysts believe that the IJN made a major strategic mistake by depending on converted carriers such as Ryuho instead of building purpose-built ships from the start which resulted in amplified losses of skilled pilots. The resourceful conversion program resulted in carriers that performed poorly in contemporary carrier warfare as demonstrated by Ryuho during the Battle of the Philippine Sea.

Japan’s naval strategy based on the Kantai Kessen doctrine predicted that victory would come from one decisive battle engagement. The IJN Ryuho’s mission in the Philippine Sea followed Japan’s naval strategy yet suffered from the IJN’s failure to properly assess American air power and radar technology which resulted in devastating losses. Japan’s post-1944 defensive strategy required that all available resources like Ryuho perform transport and training duties to postpone their defeat.

Final thoughts

The IJN Ryuho emerged as a wartime necessity when Japan transformed a submarine tender into an aircraft carrier amid the desperate days of World War II. Although its slow speed and weak construction with limited aircraft capacity restricted its effectiveness Ryuho served as a versatile transport and training platform that provided essential support to the declining air forces of the IJN. The Battle of the Philippine Sea was the only combat mission Ryuho took part in despite ending in disaster which revealed the difficulties Japan faced in sending unprepared carriers against the superior U.S. Navy. Ryuho survived multiple attacks but its history demonstrates improvisation and limited capabilities which represent Japan’s declining naval power. The narrative demonstrates how the IJN showed adaptability while acknowledging their inevitable defeat in the war.