The Izumo-Class Destroyer: Japan's First Aircraft Carrier After World War II

Japan was one of the greatest naval powers during World War II when it fielded over 20 aircraft carriers until the end of the war. However, the country scrapped all of its carriers after its defeat, and since Japan adopted a pacifist constitution, it hasn't had one since 1945.

But changing times means changing defensive requirements. Japan's Maritime Self-Defense Force (JMSDF) has the JS Kaga, an Izumo-class destroyer designated as a helicopter destroyer. This ship has flat top that allows five helicopters to operate on it deck simultaneously. It has a typical load of seven choppers but can be outfitted to carry as many as 28.

In 2018, Japan plans to purchase 42 F-35Bs, which are designed to take off on short runways and land vertically. It has modified its Izumo-class helicopter destroyers to carry jets, turning them into full-fledged aircraft carriers: the first ones Japan would have since its surrender to the United States almost 80 years ago.

Since the Japanese constitution prohibits its military from acquiring offensive weapons, the Izumo-class is made up of two ships, the Izumo and the Kaga, and is considered a defensive weapon with a destroyer designation. Nevertheless, China claims that upgrading the Izumo-class ships to carry F-35Bs "changes the warships' nature from a defensive to offensive." Even if that were the case, the Izumo-class ships only have a small displacement of 19,500 tons — practically lightweight compared to America's USS Nimitz (97,000 tons), which is one of the largest ships in the world, and China's Shandong (66,000 tons).

Aside from that, the introduction of advanced ship-killing missiles means that it can now hit targets hundreds or even thousands of miles away, while the defensive range of most ship-based weapons systems only have a range of about 100 miles. Thus, Izumo-class ships carrying F-35Bs would be crucial for the JMSDF in helping it maintain control of sea lanes within Japan's territorial waters.

The U.S. Naval Institute Proceedings magazine even said in its 2019 issue, "In an 'island grab' scenario, the F-35B would be invaluable in establishing the local air control required for Japan's new amphibious regiment to retake remote islands." The publication may have said this in relation to the ongoing dispute of China and Japan with the Senkaku Islands.

The Kaga is being upgraded to aircraft carrier status, so it will see some minor changes. The JMSDF shared on X last December 2023 that the special modifications on the Kaga are nearing completion. The Izumo bow is now shaped as a rectangle instead of the original trapezoid, making it easier to launch F-35s from its deck.

Aside from this, the two ships will get reinforced decks to support the weight and heat of the F-35B Lightning IIs, plus the addition of guidance equipment and painted lines to help with the operation of fighter aircraft.

The JMSDF will also make some interior changes to the ships, although it did not specify what these changes will be. It expects the interior upgrades to begin by March 2027, so there's still some time before Japan has a fully operational light aircraft carrier in its naval fleet.

The Izumo-class Kaga might sound familiar to World War II historians. That's because it shares a name with another aircraft carrier in the then-Imperial Japanese Navy (IJN). The Kaga was the third IJN aircraft carrier, which entered service in 1928.

The Kaga was part of the Japanese fleet that bombed Pearl Harbor in 1941 and it also took part in the Battle of Midway the following year. It was during this battle that the ship took four bomb hits, igniting the fuel onboard and causing a massive explosion. The crew tried to save the ship, but after 33 hours of battling the flames, the Kaga eventually capsized and sank.

The original Kaga is much larger than the new one, with a displacement of 38,200 tons. It also has a complement of 90 aircraft, which is so much more than the 28 helicopters the new Kaga is designed to carry. And, given that the F-35B is much larger than most rotary-wing aircraft, it will likely carry fewer fighter planes.