Japanese aircraft carrier Hiyō

Hiyō: The Imperial Japanese Navy’s Forgotten Aircraft Carrier

Imagine a ship that was once envisioned as a luxurious passenger liner, destined to sail the seas with elegance and grace. But fate had other plans for Hiyō, the name ship of her class, originally planned as Izumo Maru. In 1941, this grand vessel was converted into an aircraft carrier for the Imperial Japanese Navy, marking the beginning of a tumultuous journey that would see her serve in some of the most pivotal battles of World War II.

From Luxury Liner to Carrier

Hiyō’s transformation from a passenger liner into an aircraft carrier was no small feat. With a length of 220 meters and displacing 24,150 tonnes at standard load, she was designed with speed in mind. However, the conversion process posed significant challenges. The ship had to be modified to accommodate the needs of naval aviation, including hangars for aircraft and fuel storage.

Design and Armament

The design of Hiyō reflected a compromise between luxury and military necessity. She was equipped with a pair of geared steam turbine sets, allowing her to reach impressive speeds. The ship had two superimposed hangars, providing space for the air group that was initially intended to consist of 12 Mitsubishi A5M ‘Claude’ fighters, plus four in storage, 18 Aichi D3A ‘Val’ dive bombers, and 18 Nakajima B5N ‘Kate’ torpedo bombers. This complement was revised several times during the year, with a final air group consisting of 21 Zeros and 9 B5Ns.

Armour and Fire Control

Despite her conversion, Hiyō’s design limitations meant that she could not add much armour. The ship had a double hull, with two plates of Ducol steel protecting the sides of the machinery spaces. These spaces were further subdivided by transverse and longitudinal bulkheads to limit any flooding. Two Type 94 high-angle fire-control directors were fitted on each side of the ship to control the Type 89 guns.

Operational History

Hiyō’s operational history was marked by a series of battles and engagements. She participated in several attacks against American forces in the Guadalcanal area as part of the 3rd Fleet. On October 16, her aircraft attacked USS Aaron Ward and USS Lardner without effect. The defending Zeros were able to shoot down one Wildcat while losing a fighter.

After repairs, Hiyō returned to Truk for training before returning to Japan. Her air group consisted of 27 Zeros and 12 D3As and participated in several attacks against Guadalcanal and New Guinea. On April 7, her aircraft formed the third wave of attacks on Guadalcanal.

Final Days

The final days of Hiyō were tragic. She was torpedoed by USS Trigger on June 8, 1944, during an attack on Milne Bay with a large force. Her air group was flown to Truk by July and then to Singapore in November. On June 20, 1944, Hiyō participated in the Battle of the Philippine Sea. During this battle, she was sunk by a gasoline-vapour explosion, resulting in the loss of 247 officers and ratings.

Legacy and Impact

The story of Hiyō is a testament to the ingenuity and resourcefulness of naval engineering during World War II. Her conversion from a passenger liner to an aircraft carrier highlights the adaptability required in wartime. Despite her limitations, she played a significant role in several key battles, contributing to the strategic efforts of the Imperial Japanese Navy.

Hiyō’s legacy lies not only in her operational history but also in the lessons learned about ship design and naval aviation. Her story serves as a reminder of the complex interplay between technology, strategy, and human ingenuity in the face of conflict.

In conclusion, Hiyō was more than just a ship; she was a symbol of the Imperial Japanese Navy’s ambitions during World War II. From her conversion to an aircraft carrier to her final moments in the Philippine Sea, Hiyō’s journey is a fascinating chapter in naval history that continues to captivate historians and enthusiasts alike.