Japan Completes Key Conversion of JS Izumo into F-35B-Capable Platform

Japan converts JS Izumo into F-35B-capable light carrier, marking a major step in naval modernization and Indo-Pacific maritime capability expansion.

Cover Image Attribute: The JS Izumo aircraft carrier with its new bow section at the JMU dry dock in Isogo, Yokohama. / Source: Japan Maritime Self-Defense Force (JMSDF, 海上自衛隊) 

The ship can accommodate as many as 28 aircraft, or 14 larger ones. Its initial air wing is expected to include seven anti-submarine warfare helicopters and two search-and-rescue helicopters. For additional missions, it can transport up to 400 personnel and around 50 3.5-ton trucks or similar equipment. The flight deck features five landing spots, enabling simultaneous helicopter takeoffs and landings.

On April 17, 2026, Japan Marine United (JMU, ジャパン マリンユナイテッド株式会社) floated out the JS Izumo (DDH/CVM-183) from dry dock and berthed it along the pier at JMU’s Isogo Shipyard in Yokohama after widening the warship’s bow, completing a major structural modification that transforms the vessel into a light aircraft carrier capable of operating F-35B stealth fighters.

The changes to the Izumo mirror those already made to its sister ship, the JS Kaga (DDH/CVM-184), marking a significant milestone in Japan’s naval modernization. The alterations expand the flight deck and improve the ship’s ability to support short takeoff and vertical landing (STOVL) operations, reflecting Tokyo’s gradual shift toward enhanced power-projection capabilities amid rising tensions in the Indo-Pacific.

The Izumo-class vessels were originally designed as helicopter destroyers, a designation that adheres to Japan’s pacifist postwar constitution, which renounces offensive military capabilities. But both ships were built with provisions — including large hangars and elevators — that have allowed their conversion into de facto light carriers without constructing entirely new hulls.

The modernization of the Izumo proceeded in two phases. The first, completed in June 2021, strengthened the flight deck to withstand the intense heat generated by F-35B engines, added navigation lights and painted yellow deck markings. In October 2021, the ship successfully hosted two United States Marine Corps F-35Bs from the 242nd Marine Fighter Attack Squadron, which conducted vertical landings and short takeoffs off the coast of Japan.

The second and more extensive phase began in November 2024. Workers reshaped the ship’s bow from its original curved helicopter-friendly design into a rectangular form similar to that of the Kaga. Japanese defense officials have said the modification increases the usable flight deck area and improves aircraft handling.

The Japanese Ministry of Defense (Bōei-shō, 防衛省) allocated about $125 million specifically for the Izumo’s upgrade as part of a broader $2.78 billion commitment in 2024 to support F-35B integration across the program. The work includes internal modifications to control rooms, maintenance spaces and other aviation-related facilities. Full operational capability for the Izumo is expected by 2027.

The Kaga, the lead ship in the class, has already conducted advanced testing. In October 2024, it operated off the coast of California with F-35Bs, including night operations and maximum-load exercises, providing data that has informed the Izumo’s conversion.

Japan has ordered 42 F-35B Lightning II fighters, with the first aircraft delivered to Nyutabaru Air Base in Miyazaki Prefecture. By mid-2025, three had arrived, and additional deliveries are scheduled through 2026. The Japan Air Self-Defense Force operates the jets, which will deploy aboard the carriers. The reactivation of the 202nd Tactical Fighter Squadron, previously a land-based F-15J unit, signals the military’s intent to build a dedicated carrier-based aviation capability.

The program also includes installation of systems such as the Joint Precision Approach and Landing System (JPALS) for all-weather operations. Crew training and doctrinal development continue, with Japanese pilots scheduled to begin regular carrier qualifications in 2025.

Officials have framed the conversions as defensive enhancements and improvements in interoperability with allies. The United States and Britain have participated in testing aboard the ships, underscoring the bilateral and multilateral dimensions of the effort.

The modifications come as Japan responds to evolving security challenges in the region, though Tokyo continues to emphasize its commitment to a strictly defensive posture. By adapting existing hulls rather than building new carriers, the program achieves cost efficiencies while expanding the Maritime Self-Defense Force’s flexibility for maritime domain awareness and rapid response.

As the Izumo undergoes final outfitting and sea trials, attention will turn to integrating the growing F-35B fleet. With both ships in the class now structurally modified, Japan is on track to field two operational platforms for STOVL fighter operations, a notable evolution in its naval posture since the end of World War II.

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