Japan’s 2 Largest Warships Will Be Docked in FY 2026 and FY 2027

The Japan Maritime Self-Defense Force (JMSDF) has started the final stage of converting its helicopter carrier JS Izumo (DDH 183), one of the two largest ships in the service, into an aircraft carrier capable of supporting the operations of the short take-off and vertical landing (STOVL) F-35B Lightning II Joint Strike Fighter.

The 248 meter-long, 24,000-tonne Izumo is homeported at the JMSDF Yokosuka Base in the same prefecture.

A spokesperson at the JMSDF confirmed to The Diplomat that the Japan Marine United (JMU) Corporation began conducting refit work on JS Izumo, the lead ship of the Izumo-class, at the company’s Isogo shipyard in Yokohama City of Kanagawa Prefecture, south of Tokyo, on November 1.

A full month later, on December 2, the Izumo was seen by this author from the quay near the Isogo Fishing Piers on the opposite shore in Yokohama. It has already installed several large cranes and other structures on its flight deck and bridge.

According to the JMSDF, the modifications to its two Izumo-class helicopter carriers – JS Izumo and JS Kaga (DDH 184) – are underway in two main stages to coincide with the vessels’ periodic refit and overhaul programs, which take place every five years. The modifications are aimed at strengthening deterrence at sea against the Chinese military, which is making aggressive advances into the East and South China Seas and the Pacific Ocean.

There are only 20 airfields in Japan with runways of over 2,400 meters, which are necessary for the Japan Air Self-Defense Force (JASDF) to operate fighter jets. In particular, in the Pacific Ocean, there is only one such air base, on Iwo Jima, which means that the JASDF has limited operational infrastructure in the region at this point.

For this reason, in order to protect Japan’s airspace and territorial waters in the vast Pacific Ocean, the government is aiming to convert the Izumo-class helicopter carriers into light aircraft carriers so that F-35Bs can take off and land at sea.

The JMSDF started the first part of the two-stage modification for the JS Izumo in March 2020, and completed it in June 2021. The first stage involved upgrading the carrier’s fight deck and fitting heat-resistant deck spots for vertical take-offs and landings. A single yellow marking line (tramline) was also drawn on the flight deck from bow to stern. This line is provided on the flight deck for carrier-based aircraft to guide pilots during takeoff and landing.

As part of its second and final modification, the Izumo will be undergoing the major conversion of the bow section of its flight deck. This is needed because the current bow – a trapezoid shape – is too small to fully suppress turbulence when operating the F-35B. The modification will add decks to the sides to make the bow rectangular.

The Izumo’s conversion to a light aircraft carrier is scheduled to be completed by the end of fiscal year 2027. That means the ship will remain docked at the shipyard in Yokohama for the next three years.

Meanwhile, the Kaga, which is homeported at the JMSDF Kure Base in Hiroshima Prefecture, completed the first stage of its conversion to a light aircraft carrier at the JMU Kure Works in Kure City in April 2024. Its bow has been already converted to a rectangular shape ahead of the Izumo. The second-stage conversion of the Kaga will begin in fiscal year 2026, with all conversions scheduled to be completed by fiscal year 2028.

This means that two Izumo-class helicopter carriers will be in dock for refit during fiscal years 2026 and 2027. Will Japan’s maritime defense be sufficient without Japan’s two largest warships?

There are worries this might create a power vacuum that could be exploited by hostile countries such as China, Russia, and North Korea. Also, the two Izumo-class destroyers will be unavailable for use in the event of a disaster like the Great East Japan Earthquake that occurred in March 2011, which could affect emergency relief and medical activities.

Asked these questions by The Diplomat, a spokesperson at the JMSDF said on December 6, “It is true that there will be periods when the regular inspections and special modifications of JS Izumo and JS Kaga overlap, but during those periods, the operations of other ships owned by the Maritime Self-Defense Force will be adjusted to minimize the impact on maritime defense.”

The spokesperson added, “We are always maintaining our defense capabilities, taking into account the number of ships that can be deployed. Therefore, we have ships on standby at all times that can respond to disasters, so there will be no impact.”

Japan’s Ministry of Defense also plans to operate F-35Bs from the JASDF’s Nyutabaru Air Base near the southeastern coast of Kyushu Island. By deploying F-35Bs to Nyutabaru, Tokyo is aiming to enhance Japan’s ability to defend its remote southern islands, including those near the disputed Senkaku/Diaoyu Islands. These islands are controlled by Japan but claimed by China and Taiwan.

The ministry plans to acquire 42 F-35Bs, along with 105 F-35As. The first six F-35Bs will be deployed to Nyutabaru at the end of the current fiscal year 2024.