Japan converted two luxury ocean liners into frontline aircraft carriers during World War II.

Countries & Cities · Published 15 October 2026 Swipe more like this →

In short: Originally ordered as high-speed passenger ships, the Hiyo and Junyo were redesigned mid-construction to serve the Imperial Japanese Navy. These massive conversions featured unique engineering compromises, including merchant-style machinery and specialized flight decks, ultimately playing a significant role in the Pacific theater before meeting their respective ends.

In late 1938, the Nippon Yusen Kaisha shipping line ordered two luxury liners, Kashiwara Maru and Izumo Maru. Recognizing their potential, the Japanese Navy subsidized 60% of the construction costs in exchange for design specifications that allowed for rapid conversion into aircraft carriers. This included structural reinforcements like double hulls, aviation gasoline storage, and specialized hangar layouts. To balance the Navy's speed requirements with the operator's fuel efficiency goals, the ships were designed to reach 25.5 knots, though their merchant-style machinery was significantly heavier than that of purpose-built carriers.

Commissioned in 1942, the ships—renamed Hiyo and Junyo—were vital assets during the Guadalcanal Campaign. They featured an innovative island integrated with the funnel, angled 26 degrees to clear exhaust from flight operations. Despite these advancements, their origins as passenger liners limited their armor protection. They relied on Ducol steel plating around machinery and magazines, but were ultimately vulnerable to the intense combat conditions of the Pacific. Hiyo was lost in mid-1944 to a gasoline vapor explosion following a torpedo hit during the Battle of the Philippine Sea.

Junyo survived longer but faced a difficult end. After being damaged in the same 1944 battle, she was used as a transport before being torpedoed in December. By March 1945, repairs were deemed uneconomical, and the ship was effectively hulked. Following Japan's surrender, American evaluators declared her a total loss, and she was scrapped between 1946 and 1947. The Hiyo-class remains a fascinating case study in wartime necessity, demonstrating how civilian infrastructure was rapidly adapted to meet the desperate demands of naval aviation.

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